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Audio >> SKA-audio DIY >> Simple LDR volume control!
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Message started by Greg B. on May 6th, 2007, 6:04pm

Title: Simple LDR volume control!
Post by Greg B. on May 6th, 2007, 6:04pm

All manner of methods are being used for volume control and I believe some commercial ones are using LDRs as a dividing element with their value being determined by DC through an attached LED.  

We should build one. ;)  I was thinking of a simple shunt to output through a 10K resistor from source.

Maybe we could even remote control it to serve a number of channels? Any comments?

Title: Re: Simple LDR volume control!
Post by rabbitz on May 6th, 2007, 10:09pm

Like George's Lightspeed?

Title: Re: Simple LDR volume control!
Post by AvgJHbilly6tooth on May 7th, 2007, 5:32am

Sounds more like the Melos one which I think used a series 10K resistor and shunt LDR to ground. That would need only 2 LDR for stereo. George's Lightspeed uses 4.

Title: Re: Simple LDR volume control!
Post by Greg B. on May 7th, 2007, 6:52am

Yes that's it Joe - a simple voltage divider.
As I've never experimented with the audio aspects of LDRs that would be a good start.

Having a look at a few I see that many of them are most efficient in the circa 550nm wavelength region - right in the green, where the most lux efficient LEDs are. Good start. I checked out some coupled ones in the one pkg but they seem to use red leds if Vf is any indication.

So I think a separate LDR and a high brightness green LED might be a good starting point. House it later. Matrixboard for mounting.

Greg

Title: Re: Simple LDR volume control!
Post by stuartk on May 8th, 2007, 1:50am


Greg B. wrote:
Yes that's it Joe - a simple voltage divider.
As I've never experimented with the audio aspects of LDRs that would be a good start.

So I think a separate LDR and a high brightness green LED might be a good starting point. House it later. Matrixboard for mounting.

Greg


Assuming the LDR presents a stable simple resistance that varies linearly with light input, it should be perfect. It's not in the signal path, so nobody can complain about that. :) The taper of the control would then be set by the taper of the pot controlling the LED (assuming the light output of the LED also varies linearly with input).

I guess if the LDR's or LED's response isn't linear, then it might get more complex.

I once built a lightmeter for photographic use with a cadmium photocell, but I don't remember much about the characteristics of the devices.

A piece of shrink wrap tubing might be a good way to couple the LDR and LED.

It does seem to me that the quality of the control is going to be dependent upon the quality of the pot that controls the LED. Problems with the pot will produce problems for the control. So how is this an improvement on simply using a mechanical variable resistor as a shunt to ground and avoiding the LED and LDR?

In other words, it's an interesting project, but will it improve performance or reliability in any way?

Does it become more useful if remote control is thrown in? (It would seem to possibly offer some isolation between the remote control circuitry and the variable shunt resistor.)


Title: Re: Simple LDR volume control!
Post by Greg B. on May 8th, 2007, 7:27pm

Well the search is on for low resistance (illuminated reasonably) LDRs

The max impedance is the input resistance of the amp at 28K so theres a loss of 20 log (28/(28+10) or 2.65dB at maximum.  The minimum at reasonable lux (intensity) will set the range of volume control.

For example if it drops to 50 ohms then the (50//28K)/10K gives -66 dB so the range is 63.35dB. pretty good.

So to find an LDR with good low resistance at green LED mA lux!

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on May 9th, 2007, 12:25am

I've read the Lightspeed thread on DIYA and they seem to concentrate on the Silonex parts NSL32SR2 & R3.

These are complete optocouplers ( LED & LDR in one part) specifically designed for audio?(whatever that means - comprised of composite Cadmium Sulfide & Cadmium Selenide).

It might be worthwhile looking at the application notes on Silones for these parts: Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!


The main problem with using these parts is getting matched pairs - it requires about 10 NSL23SR2S (the sorted part - sold at a higher price).

The reported distortion is med-good although the application notes state that

It further states that series attenuator problem is
Quote:
the circuit's usefulness is limited by the non-linear relationship between LED current and attenuation, and high distortion levels at any attenuation level below -10 dB


And Shunt attenuator problem is
Quote:
However, the time constant for increasing the gain will be approximately 300 msec which will cause a noticeable lag in response


So it seems to recommend series/shunt attenuator fed by a constant current source with temperature dependent compensation circuit - circuit attached

Hope this helps - as I'm interested in the outcome of this thread & using something along these lines.

John

Title: Re: Simple LDR volume control!
Post by jkeny on May 9th, 2007, 2:45am

Another part VTL5C4/2 (Perkin-Elmer), a dual element optocoupler, may well answer the matching problem of the Silonex parts but gives rise to other issues - it's on resistance is limited to 150ohm which would limit the max vol output, I think. Maybe this isn't a problem?

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John

Title: Re: Simple LDR volume control!
Post by Greg B. on May 9th, 2007, 6:57am

Hi John,

That's good info. I think the shunt arrangement has the better prospect. 300mS lag is a small thing ( I think without experiencing it) but what is the lag on a motorised pot?

150 ohm min is a problem as the range would be only 34dB!

Besides, I want to use independant LDRs and LED in this as I'm looking at one LED controlling up to 6 channels down the track. :o

Greg


Title: Re: Simple LDR volume control!
Post by jkeny on May 9th, 2007, 10:58pm

Ah multi-channel vol control - now that's useful but the matching of LEDs & LDRs will be fun!

Haven't found any LDRs with 40 , 60 ohm On resistance yest - hope there are some out there.

John

Title: Re: Simple LDR volume control!
Post by jkeny on May 10th, 2007, 12:10am

BTW there is a GB150D owner from South Africa who has built one of the lightspeed attenuators and rates it best audio bang for the buck (he posted this on the lightspeed thread on DIYA). Don't know if he is a member here and would care to post about what it brought to the GB150D - goes under the name DR.H

John

Title: Re: Simple LDR volume control!
Post by Greg B. on May 10th, 2007, 2:55pm

Yes John,

He's here - but I think he's on a trip right now.  8-)

Progress report: I picked up a couple of LDRs and a superbright green LED. Ran it at 10mA and put them right in the beam - one dropped to 150ohms, the other 450 ohms. A little variation!  :o

I could buy 100 but the yield may be quite low for ones within 6% or 0.5dB. the resistance is too high at 150 ohms. I'll look for an alternative (graded) source.

Greg

Title: Re: Simple LDR volume control!
Post by Float on May 12th, 2007, 9:05am


Greg B. wrote:
We should build one. ;)  I was thinking of a simple shunt to output through a 10K resistor from source.

Maybe we could even remote control it to serve a number of channels? Any comments?


I've done exactly this.
There's no need to make this difficult, just use the LDR george uses in the lightspeed. I think its the Silonex NSL-32r2s. On resistance is about 30 ohm, off depends on voltage and the pot, but you can have what you want.
As an example, with a 100k pot, 2.7 volts and 22ohm current limiting resistors give a range of about 35 ohm to 50 kohm for the shunt LDR. With a 10k series resistor, min attenuation is only 1db or so, and max must be 60-70db; it's not off, but its quiet.
Sorry if you don't have a clue what I'm on about; the lightspeed thread at diyaudio should help.

I'm also remote controlling this with the mv-06 kit from diyclub.biz. Works great and only $50 delivered.

It has to be said that this is one transparent preamp/ attenuator. The usual passive matching rules still apply, but its worth the effort. I tried the pukka lightspeed circuit, but for me it lost too much bass. The series 10k/ LDR shunt was much better for bass and dynamics.

Title: Re: Simple LDR volume control!
Post by jkeny on May 12th, 2007, 12:37pm

Hi Float,
Godd to hear it worked well. What is a pukka lightspeed circuit?

I believe you're right about sticking with the NSL32SRS parts as these seem to be the only ones with low on resistance. Unless, of course, Greg exposes some low R LDRs.

The only other approach I know of is not solid state - it involves 6AR8 beam deflector tubes (originally used for colour TVs). But that's for another forum.

Tell us some more about the sound. What did you use before for pot? What did it do for the SKA amp?

Thanks
John

Title: Re: Simple LDR volume control!
Post by Greg B. on May 12th, 2007, 6:07pm

Hi Float,

I haven't yet found any very low (light) resistance LDRs and those NSL32r2s are looking more attractive.

And you say you controlled it with a remote 100K motorised pot kit. That's not an Alps blue is it - the 27mm one! Does the remote and relay input switching come with that MV-01 kit?

I built a little remote volume control kit that uses RC5 code and controls from a universal remote control. It has a nice feel, with a mute function.

Greg

Title: Re: Simple LDR volume control!
Post by rabbitz on May 12th, 2007, 8:36pm

Greg

Did you get the mute to work properly on that as I have built a few of those and all were touchy. Would mute but not go back up or would not move when mute button pressed.... really fine line with adjustment. Just ended up cutting out the mute facility. They are a great value kit and I just throw the pot away though I did get a good one once.

Title: Re: Simple LDR volume control!
Post by Float on May 12th, 2007, 9:03pm


jkeny wrote:
Hi Float,
Godd to hear it worked well. What is a pukka lightspeed circuit?

Tell us some more about the sound. What did you use before for pot? What did it do for the SKA amp?

Thanks
John


Pukka lightspeed here - Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!
- it uses LDRs in series and shunt.

The sound is hard to describe, as it doesn't seem to have one. Very transparent to the deepest corners of the soundstage, but it will be influenced by loading, like all passives. I found the pukka lightspeed bass light with a 100k input amp, so I switched to a fixed series /LDR shunt and all was well. A pot (alps blue or black), even as a shunt, sounds muffled, less dynamic and lacking detail.

I've only just combined the ldr passive with the SKA, so I won't say it's a perfect combo until I've had more time, but it does sound glorious. I'd recommend trying the ldrs instead of the pot on the skpre, should be a BIG upgrade.

Title: Re: Simple LDR volume control!
Post by Float on May 12th, 2007, 9:41pm


Greg B. wrote:
Hi Float,

I haven't yet found any very low (light) resistance LDRs and those NSL32r2s are looking more attractive.

And you say you controlled it with a remote 100K motorised pot kit. That's not an Alps blue is it - the 27mm one! Does the remote and relay input switching come with that MV-01 kit?

Greg


You could // the ldrs for lower resistance, but with 90db/1 watt speakers and the SKA there's no need IMO. Its very quiet at lowest setting.

The diyclub kit does come with remote and relay switching board for 4 inputs. The pot is a cheapo 6 gang nightmare, but it makes no difference for ldr control, and you can separate grounds on the board to keep all the digital crap at bay. It's a true bargain, but it may not sound great if used as a regular pot.
The only oddity is the mute function- it just runs the pot for about 10 seconds, so you hear the motor running after the pots reached zero if the volume wasn't well round the dial.

Title: Re: Simple LDR volume control!
Post by ShinOBIWAN on May 12th, 2007, 10:35pm


Float wrote:
The only oddity is the mute function- it just runs the pot for about 10 seconds, so you hear the motor running after the pots reached zero if the volume wasn't well round the dial.


That sounds like the driver side electric window on my car. Something must have broke because you need to physically press the button to the stop the motor even after the window is up or down. Passenger side is fine though  :-/

Title: Re: Simple LDR volume control!
Post by Greg B. on May 13th, 2007, 5:55am

Hi Rabbitz,

This one works a treat. I picked up a $7.95 universal remote (x 8) from Crazies, thought it could come in handy. My son will set it to run everything in the house as a backup. The mute is  :thumbsup both ways. Yes my plan was to run a motorised Alps blue with it or even a 6 gang pot if the torque's not too onerous. Or the LED brightness as Float has - pity it's a 20K pot!  :(

Hi Float,

I thought you're kit was amazing value if it had a motorised Alps blue... but a cheapo 6 way  :(. As you say it's not a problem driving the LED.

Hi Shin,

Sounds like a microswitch that's lost the plot!  :o  

Greg

Title: Re: Simple LDR volume control!
Post by Float on May 13th, 2007, 6:45am

Hi Greg, i might be being unfair to the diyclub pot; it is an alps, but TBH I don't like the sound of any of the ones I've tried - blue and black included. Good tracking though, probably why they're de rigeur for commercial preamps.
Best regular pots I've tried would be the panasonic (arm and a leg for motorised) and the cermet P11 ( no motor or decent dual values for audio).
It's worth finding something good; I reckon the pot's one of the big bottlenecks in a system.

Title: Re: Simple LDR volume control!
Post by jkeny on May 13th, 2007, 8:56am

Hi Float,
Do you mean that the shunt style sounded better to you than the series/shunt that is used in the lightspeed?


Title: Re: Simple LDR volume control!
Post by Float on May 13th, 2007, 9:56am


jkeny wrote:
Hi Float,
Do you mean that the shunt style sounded better to you than the series/shunt that is used in the lightspeed?


Yes, mainly because for me bass weight and dynamics were lost with the lightspeed. It's also likely that a decent series resistor will sound better than the ldr resistor. Much of the quality of this pre may come from the lack of contacts/switches rather than the quality of the resistors themselves.

Your diagram is spot on; just bodge up an adjustable lm317 and feed thru a pot and limiting resistor to have what I'm using. See earlier post for guide values.

Title: Re: Simple LDR volume control!
Post by KLe on May 13th, 2007, 5:56pm


jkeny wrote:
Hi Float,
Do you mean that the shunt style sounded better to you than the series/shunt that is used in the lightspeed?


Sounds excellent guys 8-)

Hey John, are you able to update figure2 to reflect what Float has suggested  :)
Also, where is the volume positioned?

thanks
KL

Title: Re: Simple LDR volume control!
Post by jkeny on May 13th, 2007, 11:00pm

Hi KL,
Remember I mentioned these when you were over with me last year - well here they are going mainstream maybe.

I can't update the diagram - don't know if Float is using Current source or Voltage source - maybe he can diagram it?

Here's a diagram which should explain all connections - modify as to your needs i.e substitute series opto with 10K R, change 7805 to 317, change voltage to current feed, etc

(Sorry it's a PDF so had to zip it to attach here)

John

Title: Re: Simple LDR volume control!
Post by Float on May 13th, 2007, 11:28pm

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!


This is George's diagram; same as Johns but may be easier to grasp. You can lay your board out like this.
Fixed series version is of course even simpler. I'll try to scan something tomorrow if I can.


Title: Re: Simple LDR volume control!
Post by jkeny on May 14th, 2007, 1:12am

Hey Float,
Now I'm confused - I thought you were using 1 opto per channel in a shunt config?

Looking forward to the schematic scan

John

Title: Re: Simple LDR volume control!
Post by Float on May 14th, 2007, 6:23am


jkeny wrote:
Hey Float,
Now I'm confused - I thought you were using 1 opto per channel in a shunt config?
John


Sorry, yes I am. I posted the original lightspeed diagram in case anyone missed it in the diyaudio thread. Same schematic as yours of course.
You've probably worked out exactly what I've done, only one opto in shunt per channel and only a single gang pot. The variable 1k resistors are optional for balance; I've not bothered.

There's probably many ways to control the led shunt, just keep current below 20ma. Different voltages and pot values will change the taper and range, so feel free to dabble.

Title: Re: Simple LDR volume control!
Post by Greg B. on May 14th, 2007, 7:01am

OK how's this for an update from my early pic using the Silonex LDR/LED unit as Float suggested.

I picked up a 2M (d.g.) log pot which is ~ 340K at 1/2 rotation that might give more 'dark' range.

Title: Re: Simple LDR volume control!
Post by Float on May 14th, 2007, 9:27am

Nice one Greg, that saves me a job. The cap over the led is a worthwhile addition.
All thats left is to build it and see what it does.

The power supply does matter; I'm using an SLA battery to power a lm317, but use whatever you prefer.
As long as you adjust the limiting resistor to keep the led current under 20ma you can play with supply volts and pot values to give the shunt resistance and rate of volume change that you like. I don't think you need more than 100k, between 50k and 100k is ideal IMO.

Title: Re: Simple LDR volume control!
Post by Greg B. on May 15th, 2007, 6:11am

OK So the big problem is matching. I can buy a fair few and match them so there should be little wastage. The NSL-R2 one goes lowest so would be the one to use. Are Silonex approachable for small orders or is there another good value source. If I can pair all units there would be zero wastage :thumbsup as, I believe they are, all graded in a narrow range so only need to be paired.

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 7:10am

Hi Greg,

Best price I can find is $2.45 each from Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!
part no 699-3011. RS have them in UK (Australia also)

RS Australia seem to have them at $5.22 (I don't think that is Aus$) Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!


As for matching the sorted part is what is needed NSL-32SR2S but although it says on the datasheet that it is also graded into ranges by letter A to G it also says that it cannot supply all parts from the one grade.

I have emailed Allied(US) & RS(Ireland - stg£1.60 + £10 shipping) asking can they provide all parts from the same grade letter (this is printed on the part) but have received no reply from either.

If your are considering buying some I for one would be interested in two pairs along with a Skepre board and there may be more here in Ireland. At the beginning of June there is a "national meeting" of all the DIY audio people in Ireland - all 3 of us. We will be listening to various equipment including my GB150, some tube amps, Quad speakers,Rogers Speakers. I will report back here the outcomes if there is interest.

Hope this helps the cause
John

Title: Re: Simple LDR volume control!
Post by KL. on May 15th, 2007, 7:45am


jkeny wrote:
If your are considering buying some I for one would be interested in two pairs along with a Skepre board and there may be more here in Ireland. At the beginning of June there is a "national meeting" of all the DIY audio people in Ireland - all 3 of us. We will be listening to various equipment including my GB150, some tube amps, Quad speakers,Rogers Speakers. I will report back here the outcomes if there is interest.

Hope this helps the cause
John

Hi John
The club has started ... well done  :)

Hey Greg,
me too is interested ... also, for use with my SKpre  8-)

Well done Guys
KL


Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 7:49am

Thanks KL,
Yes I remember you telling me how you organise it. Any chance you could refresh me by PM?

EDIT: I forgot to mention that I also emailed Silonex (Margy Manganiello <mmanganiello@silonex.com>) and this was their reply:


Quote:
Hi John,

Thank you for your interest in our products. Farnell does carry the sorted version of the NSL-32SR2. It would be our product, NSL-32SR2S. We, however cannot guarantee that they would all be from the same grade. We also sell this part through Allied Electronics, you can visit their website at Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!
. Through distribution would be the quickest way for you to purchase this part.

Best regards,

Margy Manganiello
Customer Service Manager
Silonex Inc.
A Casco Products Company
Tel: 514-768-8000 X130
Fax: 514-768-8889


John

Title: Re: Simple LDR volume control!
Post by Greg B. on May 15th, 2007, 8:45am

Excellent - I'll see what I can do.

Any idea on the gradings A to G?  Resistance I presume - lowest is A?

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 8:51am

I don't know what the gradings signify

You may probably have more success in the grading issue if ordering a larger qty - I was only looking for 10

Best of Luck

John

Title: Re: Simple LDR volume control!
Post by Float on May 15th, 2007, 9:40am

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Not seen this yet?  ;)

Don't worry about gradings, I've got 'E's and they go to 30 ish ohms. Whoever picks and packs is likely to take them all from the same bin, so you'd be unlucky to get different selections.
Even then, you'll be amazed how much they vary when you match them, and amazed again how little that seems to matter once you've built the thing.

Title: Re: Simple LDR volume control!
Post by Float on May 15th, 2007, 9:57am

I'm in the UK, so I got mine from RS (shipped from Allied, US), cost was about £40 for 16 units. £10 of that was surcharge because they had to come from US.  :'( From this I got 6 pairs and 4 oddballs. You may be fussier than me, but until I've tried the loosest matches I'll assume they're usable. You can add a trimmer to help balance.
It didn't seem cheap, but then I thought what a good pot or stepper cost.

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 9:57am

So how critical is it to match them? It seems from other threads that even with the matching there are differences accross the two channels at points on the vol knob i.e they can only be matched approx at a number of settings

I'm just wondering if we could use a seperate pot for each channel like a balance control and basically match the vol accross channels by ear?

Or could the exact matching accross channels be achieved on the fly by some servo control?

John

Title: Re: Simple LDR volume control!
Post by Float on May 15th, 2007, 10:22am

Good point John, if you're happy with a pot for each channel the matching is not really needed.
I matched mine at 3 points using a battery and 3 resistors to give 3 current levels. A bit of a pain, and when you see the results you wonder if ANYpairs are good enough.
But, I use a single pot, and no trimmers, and the centre image seems about right without wandering when the volume is altered. I've not really listened for this though.

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 10:33am

To carry this further if the pot was remote controlled, this balancing could be done from the listening position - I'm liking this idea more & more. One pot for gross vol adjust & another for fine channel balance.

Ok so what's the cost of 2 remote  boards - 2 *$32 from DIYclub - ok.

Am I missing something or a more elegant solution?

John

Title: Re: Simple LDR volume control!
Post by Float on May 15th, 2007, 10:44am

I think the remotes would operate each other - unless you can reprogram the controller.
I'd hope matching alone would get you acceptable balance. Maybe cross that bridge if you need to?

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 11:00am

OK, here's another idea to avoid matching of optos:

Use a cheap stepped attenuator with different valued Rs which match the opto to which it is connected & gives the same output for both  optos

Just see your post Float - Ok buy one remote pot from DIYclub & one from elsewhere (Greg has one - don't know if it's a kit?)

Hey Float - any spare optos you wish to send me?

John

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 11:15am

Just one other question - as a clean supply for the opto is critical, what effect does passing 5V through a pot have (the LED control)?

I promise I'll stop posting - have to go to bed

John

Title: Re: Simple LDR volume control!
Post by Float on May 15th, 2007, 11:22am


jkeny wrote:
OK, here's another idea to avoid matching of optos:

Use a cheap stepped attenuator with different valued Rs which match the opto to which it is connected & gives the same output for both  optos

Just see your post Float - Ok buy one remote pot from DIYclub & one from elsewhere (Greg has one - don't know if it's a kit?)

Hey Float - any spare optos you wish to send me?

John

The stepper should provide perfect matching. Hard to do remote though?

Different kits may still use the same rc5 philips code?

Sorry John, already gave away my spares!

Title: Re: Simple LDR volume control!
Post by Float on May 15th, 2007, 11:29am


jkeny wrote:
Just one other question - as a clean supply for the opto is critical, what effect does passing 5V through a pot have (the LED control)?

John

TBH I don't know; though no reliability probs reported AFAIK.
If you're feeling brave, you could work though the diyaudio thread; it's a bit wayward, but there's been discussions of PS differences and all sorts.

Title: Re: Simple LDR volume control!
Post by mikeg on May 15th, 2007, 11:55am

I haven't looked at the trhead at diyaudio, and I understand the reason for doing this but, every time I've used opto Rs in the past they had horrible reliability and repeatability issues. Then, the resistance curve would change over time.

Am I missing something?

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 6:35pm

Hi Mikeg,
The commercial products using these seem to be going without incident for a long time - have a read of the DIYA thread.

Final thought - what about digital vol control - this might be even easier to match both sides?

John

Title: Re: Simple LDR volume control!
Post by Greg B. on May 15th, 2007, 7:18pm

Hi John,

I'm working on an expandable digital volume control within the next coupla months, as an option..

I think if these LDR/LED things deteriorate over time and they are excellent performers as claimed, then we can replace the 'sealed unit' at a reasonable cost... it's underway.

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on May 15th, 2007, 7:28pm

Bong Greg,
That sounds like the winner - I'll probably buy two unmatched optos and have a listen while waiting for your remote controlled? perfectly matched? opto digital control.

John

Title: Re: Simple LDR volume control!
Post by KL. on May 15th, 2007, 7:53pm

Absolutely Greg  8-) keep us all informed :thumbsup

John, I'm excited also  ;D

Title: Re: Simple LDR volume control!
Post by jkeny on May 16th, 2007, 6:45am

Hey Guys,

Here's my request to Allied:

Quote:
Even though these are sorted parts, I need tighter matching than would be provided with random selection of parts. As the sorted part is also graded could I request all parts to be provide from the same grade letter (A,B,C,D,E,F or G). This should be possible as the grade letter is printed on the part.


Just got this email back from them:

Quote:
I am sorry the factory always send different grades
there is really no way to process as you have requested


So I can only conclude that for multi channel vol pot a large qty would need to be ordered in order to get a quad or more matched parts.

It would seem that digital control is the way to go with Autocalibration if possible.

What do you guys think?

Here's a quote from DIYA about this and the graph attached:

Quote:
I have developed a µC circiut to digitaly control a current source and to measure the resistance of LDRs for matching purposes. See measurement details in the attached file. The Pot-Solution (100K log) to adjust the current of the LDR's is not very comfortablemm, because it is to sensitive. So I will do that at a later point with a µC including remote control and fixed steps for attenuation.

Conclusion of measurement: to match the LDR's 2 or 3 measurement points are enough, because the progression is always near the same. If you are comfortable with channel accuracy of arround 1-1,5 dB you only need a few LDR's to match them. For multichannel purposes or accuracy of 0.5 dB you have to measure much more pieces to find matching pairs.

Title: Re: Simple LDR volume control!
Post by Greg B. on May 16th, 2007, 6:27pm

OK update is I have 26 coming - should be here in a week. I'll check the match/grading and see if we can get a good few pairs...

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on May 17th, 2007, 10:17am

Greg,
Looking forward to your test results. Can I ask a general question as to why these optocouplers are suitable for audio but other photo transistor parts are not

Not being technical enough to understand the specs can somebody tell me if this photo coupler part is suitable for audio. If not can you explain why? Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!


Thanks for bearing with me so far
John

Title: Re: Simple LDR volume control!
Post by KL. on May 26th, 2007, 4:20pm


Greg B. wrote:
OK update is I have 26 coming - should be here in a week. I'll check the match/grading and see if we can get a good few pairs...

Greg

Hi Greg
Just wondering how this is coming along  :)

thanks
KL

Title: Re: Simple LDR volume control!
Post by Greg B. on May 27th, 2007, 6:28am

Hi KL - I believe they're in transit.

Might see them Monday. :o

Greg


Title: Re: Simple LDR volume control!
Post by KL. on May 27th, 2007, 3:18pm

Excellent Greg, look forward to the results  :)

Title: Re: Simple LDR volume control!
Post by jkeny on May 29th, 2007, 10:04am

Hi All,
I tested some Silonex NORP? given to me and they seem to have a min R of 30 ohm in sunlight - will test with different colour LEDs but it looks promising though. Problem is I don't know what part no it is just says Silonex NORP on the part - theylook like the top photo


Title: Re: Simple LDR volume control!
Post by Greg B. on May 30th, 2007, 8:32am

Hi John,

Well they look nice as well. I didn't know about those. :-?

Hmmm...


Title: Re: Simple LDR volume control!
Post by jkeny on May 30th, 2007, 9:14am

I found out they are Silonex NORPS12 parts - cheap too $0.68 each.

Looking at the datasheet the min R only goes down to 5K I have measured a number of them now in electric light and they all go down to around 30-50 ohm.

Looks like we might have a winner here - just need to test different coloured LEDs & match up a number of them

Hope this helps

John

Title: Re: Simple LDR volume control!
Post by KL. on May 31st, 2007, 11:29am

Excellent guys,

Greg are you able to test some of these?

John have you already tested and tried these?

Title: Re: Simple LDR volume control!
Post by jkeny on May 31st, 2007, 5:41pm

Hi KL,
No I haven't put them together in a circuit yet - should do over the weekend. My main problem is finding a tube into which I can put LDR in one end and LED in other end. The LDR is much wider than the LED. I'm going to ignore matching & see how much of an irritant this is i.e. how often I have to adjust the balance knob?

I made a mistake in the pricing - it's 0.85 in £ not $ and excl VAT so something like $2.00 in reality - not much cheaper than the NSL32 parts and these contain the LED already inbuilt into assembly.

John

Title: Re: Simple LDR volume control!
Post by stuartk on Jun 1st, 2007, 2:51am


jkeny wrote:
Hi KL,
No I haven't put them together in a circuit yet - should do over the weekend. My main problem is finding a tube into which I can put LDR in one end and LED in other end. The LDR is much wider than the LED. I'm going to ignore matching & see how much of an irritant this is i.e. how often I have to adjust the balance knob?


Is the difference too much for some shrink tubing to work?

Title: Re: Simple LDR volume control!
Post by jkeny on Jun 2nd, 2007, 5:51am

'Fraid so Stuart - you know te size of LED well LDR is about .5 inch accross

Title: Re: Simple LDR volume control!
Post by Greg B. on Jun 12th, 2007, 3:00pm

I just received them today - thanks George!

Next to do some measurements to characterize these... :o

Title: Re: Simple LDR volume control!
Post by jkeny on Jun 13th, 2007, 2:32am

Hi Greg,
Are they the sorted or unsorted type? Do they have a grdae letter on the back? Look forward to your impressions of the sound. BTW, the series + Shunt circuit is reported to sound a lot better than shunt only circuit - I think it's to do with keeping the impedance soemwhat constant.

John

Title: Re: Simple LDR volume control!
Post by Greg B. on Jun 14th, 2007, 7:22pm

Hi John,

I can report in now.

The ones I received are all G grade and measure average ~ 185 ohms @ 1mA, 75 ohm at 5mA and 15K @ 15uA. This pretty well covers a 50dB volume range using a 10K series resistance.

Shunt or series shunt = I've had good FB each way, so lets 'suck it and see'. :thumbsup

They are very narrow grading and it's quite easy to find a pair within very narrow tolerance, so we should have a good yield of pairs that can be operated in series from a simple control circuit.

In my current PCB run I've submitted a two channel LED/LDR control circuit that mounts on a single gang volume pot.  2" x 0.5" ( equal time for imperial) with all needed components for powering from +/-15V ( like the SKpre supply)
and inbuilt HF filtering and regulation of the LED supply

Looking forward to receiving the PCBs, as these are seriously fiddly bits... ::)

Greg


Title: Re: Simple LDR volume control!
Post by jkeny on Jun 14th, 2007, 8:39pm

Hi Greg,
Good progress - great that they were all one grade - did you make any request to supply all one grade?

Look forward to your tests and your impressions of shunt Vs series/shunt

you know I'm keen on buying some pairs and/or boards from you

John

Title: Re: Simple LDR volume control!
Post by Greg B. on Jun 15th, 2007, 5:51am

George - a SKA owner lives not far from the US supplier and is using quite a few of these himself so he did a qty buy and supplied me all the same grading while he took the various. That happened to be G.

The board is a very compact one with some circuit characteristics/tradeoffs I will describe in more detail when they arrive ~ 2 weeks, for those who want to experiment with values and limits... [smiley=2vrolijk_08.gif]

Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Jun 23rd, 2007, 5:29pm

Waitin' on those boards to hear this LDR thing... ::)

Title: Re: Simple LDR volume control!
Post by Float on Jun 24th, 2007, 8:10am


Greg B. wrote:
Waitin' on those boards to hear this LDR thing... ::)


Boards???  You could knock this up on stripboard in the time it takes to drink a XXXX  :P

Title: Re: Simple LDR volume control!
Post by Greg B. on Jun 24th, 2007, 1:27pm

Heheh - I guess :-[

I haven't built anything on strip or matrix board for years. Even the prototype GB150D was on full double sided Cu clad PCB. This will be as well.  ::)

Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Jul 9th, 2007, 5:05pm

Well here it is - first pics. Boards have arrived - all labelled and stereo controlled by a single gang pot with matched LED/LDR L/R pair and LED current control range from 15uA to 10mA and RC noise filtered zener regulated supply set to run from +/-15V ( of the SKpre or DualReg).


Title: Re: Simple LDR volume control!
Post by Greg B. on Jul 9th, 2007, 5:14pm

And the connections  :thumbsup

PCB is fully ground planed on the top surface to suppress any hum and noise pickup from the high impedance circuitry.

Greg

Title: Re: Simple LDR volume control!
Post by KL. on Jul 9th, 2007, 8:17pm

Bluddy beauty, Greg  :)

... looking forward to getting one of these  8-)

... a question, does this circuit need a better volume control than the one you are using?

Title: Re: Simple LDR volume control!
Post by Greg Erskine on Jul 9th, 2007, 8:30pm


KL. wrote:
Bluddy beauty, Greg  :)
... a question, does this circuit need a better volume control than the one you are using?


hi KL.,

The pot is not in the signal path. That's the whole point of using a LDR.  :o

regards

Title: Re: Simple LDR volume control!
Post by jkeny on Jul 10th, 2007, 1:41am

Hi Greg B,
Great to see they arrived - any thoughts on the sound quality?

What price for kit?

Good work
John

Title: Re: Simple LDR volume control!
Post by Greg B. on Jul 10th, 2007, 6:14pm

Thanks KL.

Hi Greg E, that's it!

Hi John,

I can do the kit at the same price as the VolBuf - it's a bit fiddly but I think I can guarantee a 0.5dB match at 1/2 volume setting (~ -15dB and 12 o'clock) and a 40dB+ range... still fine tuning for more, trying for 50dB.

Greg


Title: Re: Simple LDR volume control!
Post by Greg B. on Jul 13th, 2007, 6:32am

OK - update.

I've been able to pair all except 2 extreme value NSLs with ~ 0-3% match for the approx -15dB level and achieved a range of ~ 45dB with max 12mA (min volume) current draw. I've also changed an onboard resistor for a red LED which not only helps achieve range but goes dim or bright in sync with the encapsulated LEDs (as an indicator?).

So I'm shipping the first few orders today for you to evaluate. I am going to try some 3V9 zeners ( for onboard reg) as soon as I can pick some up but that will necessarily lose the LED  :(  in the quest for a little more range.

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 4th, 2007, 7:50pm

Greg,

Where do the 2K2 and the LED go on this board, I assume the 2K2 is in R4 and the LED sits behind the pot? If so I assume it does not matter which 2 of the 3 holes the LED goes in as it presumably sits across one of the pairs ? Beautiful board by the way. It is extremely compact.

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 5th, 2007, 6:17am

Thanks Iain,

Yes that's correct: R4 = 2.2K (if using ~ +/-15V supply) as supplied. The LED does go in the outer two holes in the unlabelled component under the pot with the cathode at the C1 end. The cathode can be identified by a small flat on the  LED molding. The centre center middle hole  :) is for underneath connection to the ground plane and should be connected to the chassis or supply ground to ensure minimal hum and noise pickup.

NOTE: The LDR/LED packages have a white dot on them to indicate the LED polarity - this must go in the closest hole to the pot at the front (shaft edge) of the PCB on each unit. The two LDR connections are the long ones and these should bend over , while the short ones (LED) are inserted straight.


The red LED is a late addition for better control range and will also give a visual indication of volume (bright - low, dull - high). You may wish to mount the red LED from the underside on full length leads and bend it to the rear so it's in full view and unimpeded by the pot as it would be on top.

Other connections are shown -

Cheers,
Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 5th, 2007, 7:53am

Thanks Greg, desolder braid is great isn't it ;) Managed to put one of the LED/LDR combos in the wrong way around, goodness knows how but all fixed now.

I mounted the LED below as suggested, it would be very hard to mount this on top.

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 5th, 2007, 6:05pm

Yes Iain,

The design was set with a resistor but an LED gave greater range - under the pot housing is a height limitation but range is paramount!

Life's like that and then... [smiley=vrolijk_26.gif]

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 5th, 2007, 7:03pm

No problem here I prefer it mounted to the rear anyway is it is more compatible with how I plan to mount it. I actually quiite like the idea of bringing it onto the front panel, I assume I could stick it on some leads if I want to go down that route?

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 5th, 2007, 7:16pm

Hi Iain,

Yes a front panel LED would be kool I reckon!  8-) Just run the wires up.

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 5th, 2007, 8:01pm

Excellent, hope to get some pictures up soon!

Iain

Title: Re: Simple LDR volume control!
Post by Diy-dude on Aug 5th, 2007, 8:50pm

Does this mean you have started selling kits already? I'd like one of those. :thumbsup (or do I need two?)

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 17th, 2007, 4:51pm

Hi Diy-Dude,

Yes I have sent a few out for first impressions. Already I know that range is limited and it's best in a low gain, low efficiency speaker system. I'm working on extending the control range.... :thumbsup

They're very dynamic... you only need 1 for stereo but a good source of reg DC ~ 30V @ 15mA+.

Cheers,
Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 19th, 2007, 7:04am

Here are the signal flow connections for connecting the LDR Volume to a pair of SKpre modules.

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 24th, 2007, 12:26pm

Well, try as I may I cannot get these LDRs down below 40 ohms even with 25mA LED current illuminating them.  That's only 2dB lower in minimum level and not guaranteed once device spreads are accounted for...

If a big cut in level is needed I think the only simple way is to divide down the input, for a 20dB cut in gain, which will lower the minimum by the same amount but you will need to turn up the volume 20dB for average listening level.

Of course this would not be an issue with the new concept amp as it's gain is 20dB lower to start with. ;)

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 25th, 2007, 8:13am

Edit:

Scratch that, just tried Nirvana unplugged and the minimum level is too high to play at night, don't a want to wake the youngun up! Looks like I'll be testing out your reduction next  ;)

Greg,

Just listening now and the minimum volume on mine is probably just below my lowest minimum volume in normal use but still quite a level. I have half a mind just to leave well alone, what other affects would tinkering with the input in this way potentially have. I do have to crack the preamp back open to stick in a balance I forgot so I could give this a try but I don't want to compromise the sound quality in any way.

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 25th, 2007, 9:44am

Hi Iain,

Great you have the whole GB150D / SKpre / LDR Volume up with a minimum of fuss. :thumbsup

If you need a little less for that minimum volume, a change of the 10K resistors at each end of the LDR board to 22K will give a 7dB lower result. Otherwise for a greater 20dB cut, the divider will do the trick.

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 25th, 2007, 9:57am

Will try the resistor and report back, if anybody is reading this the whole system  sounds great! Look for a full report soon.

Iain

Title: Re: Simple LDR volume control!
Post by iihay on Aug 25th, 2007, 10:34pm

Greg, are 0.25W resistors ok for this?

Iain

Title: Re: Simple LDR volume control!
Post by KL. on Aug 25th, 2007, 11:09pm


iihay wrote:
Greg, are 0.25W resistors ok for this?
Iain


Hi Iain
I can answer that question ... the answer is 'Yes', 0.25W resistors are all you need to use ...

ciao

Title: Re: Simple LDR volume control!
Post by iihay on Aug 26th, 2007, 12:13am


KL. wrote:
[quote author=iihay link=1178438672/90#93 date=1188045289]Greg, are 0.25W resistors ok for this?
Iain


Hi Iain
I can answer that question ... the answer is 'Yes', 0.25W resistors are all you need to use ...

ciao
[/quote]
Hi KL,

Brilliant, I thought so, appreciate the assistance.

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by KL. on Aug 26th, 2007, 12:41am

Hi Iain
It will be very interesting to hear how much range you get with the 22k resistors. An extra 7db gives about 50db less about 12db of SKPre gain equals about 38db. Might be enough  :)

Greg mentioned a divider ... not sure what that is ... perhaps he can elaborate a bit more  :)

ciao

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 26th, 2007, 5:52am

Hi KL,

The divider is back on the last page -
Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!



Quote:
50db less about 12db of SKPre gain equals about 38db.


Not quite KL - the gain of the SKpre won't affect the control range.

Yes, a 1/4W 22K substituted for each 10K on the LDR board will lower the minimum vol by 7dB. :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 27th, 2007, 6:04am

How about a 27K? I have some of them spare!

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 27th, 2007, 6:31am

Yes 27K's worth a try for another 1.75dB. :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 27th, 2007, 7:39am


Greg B. wrote:
Yes 27K's worth a try for another 1.75dB. :thumbsup

Greg


Ok, will give it a whirl and see how it turns out.

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by iihay on Aug 27th, 2007, 8:57am

Greg

27K brings it down to below background level for all but the loudest tracks  :thumbsup Let's the voume control progress across a more normal physical range for me, I spun it before the 27K and nearly blew the back off the house  ;D

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 27th, 2007, 9:20am

Well that would appear to be the simple solution. :thumbsup

Using 27K for the series leg instead of 10K will bring max volume down by 2.5dB but reduces minimum by 8.5dB, effectively increasing control range by 6dB to 50dB, but ensuring max attenuation of 54.5dB - more practical!

I'll include a pair of 27K's in the kits in future.

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 27th, 2007, 9:35am

Believe me in my system I have plenty of volume to spare running this way, I think this is a good and very simple fix. Now how's about the balance control  :)

Iain

Title: Re: Simple LDR volume control!
Post by KL. on Aug 27th, 2007, 7:19pm

Thanks Iain/Greg for trying that  :thumbsup

Greg, if 27K is ok, can 30K be used  :question
... I can get hold of some nice RhoPoint non-inductive wirewounds that I would like to use
... so, will an extra 3K be ok  :question

ciao


Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 27th, 2007, 7:21pm

Hi KL,

30K is fine, that's an extra 1dB lower.  ;)

Hi Iain,

:-? thinking...

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 27th, 2007, 8:14pm


Greg B. wrote:
Hi KL,

30K is fine, that's an extra 1dB lower.  ;)

Hi Iain,

:-? thinking...

Greg


Think away, it's lead to great results so far  :thumbsup

Iain

Title: Re: Simple LDR volume control!
Post by Panelhead on Aug 28th, 2007, 12:32pm

Hi Gents!
 I think there is a simple way to increase the attenuation range of these LDR's. Use a LDR for both the shunt and series element. This way the ratio goes way up for Series/series + shunt.
 The increase in range will allow you to get back down to a lower series resistance. The main problem comes from needing two matched pairs instead of one pair to build a control. The series and shunt elements do not have to match, just the left and right of each.
 I work more on maintaining a good impedance balance between the channels by juggling the control pots. Use two, for a dual monon control. By diddling with pots, both my controls run 10 - 12k from wide open to max attenuation. And even with 87 dB speakers now and a normal amplifier half open is LOUD. Running a preamp with gain would be real loud.
 Glad to see your design work Greg. What you have built makes my breadboards look like crap.
Seem to remember that Melos used a large value series resistor, maybe 100K. This might work with the high impedances seen in tube gear, but it would kill the dynamics of most sources and solid state amps, plus rfi pickup. But using a 100k resistor would definately give you more control at low levels.

                         George

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 28th, 2007, 7:19pm

Hi George,

Thanks and for your help in obtaining the NSLs. :thumbsup

I wanted to keep it simple and have only the one variable element and it's worked out very well. A nice compact, continuously variable and easy to build alternative to conventional solutions.

The PCB is a big issue as it makes it a reliably reproducible design and, with the higher impedance needed for lower range extension, the presence of a ground plane is invaluable, I believe.

Cheers,
Greg

Title: Re: Simple LDR volume control!
Post by KL. on Aug 28th, 2007, 8:16pm

Hi All
An LDR in series might give more range but I don't think that it would be as good as a resistor, sonically   :(  or have I misconstrued the concept  :question

ciao

Title: Re: Simple LDR volume control!
Post by Float on Aug 28th, 2007, 8:47pm

I found the range for fixed series and the ldr series/shunt about the same. :-/
If anything, the fixed series had slightly more range, but you can use different pots/voltages/limit resistors to modify the situation somewhat. I know George is using a different arrangement to the stock Lightspeed.

One fix for an extra 6db attenuation is to parallel the shunt ldr: i.e use two of them. You may need to change the limit resistors to get the full on resistance as low as possible again.

If you just want a mute position you could simply switch a 5ohm resistor across the ldr for a c.70db attenuation.

It's less important for those using an active pre-stage, but I'm using the LDR passive, so keeping the input series resistor lower (10k) is a good thing for me.

Title: Re: Simple LDR volume control!
Post by KL. on Aug 28th, 2007, 10:26pm

Hi Float

Yes, you are right  :)
Paralleling the LDR will halve the shunt resistance  :)
What a good idea  :thumbsup

Greg, how does that sound  :question

ciao

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 29th, 2007, 5:52am

Hi KL, Float,

Yes I agree - the use of a second paralleded LDR would certainly halve the shunt resistance giving an extra 6dB lower min volume.  :) Would not be achievable with the current board though. Think I'll live with this one a little longer.

Greg

Title: Re: Simple LDR volume control!
Post by KL. on Aug 29th, 2007, 10:37am

Hi Greg

Could the LDR's be placed in parallel on the under side of the PCB  :)

ciao

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 29th, 2007, 12:08pm

Hi KL,

Yes each LDR could be soldered directly across the existing one's solder pads but it would be in parallel also on the LED side requiring double the current. The LEDs could be stacked in series but not on this board. :-/

Greg

Title: Re: Simple LDR volume control!
Post by KL. on Aug 29th, 2007, 12:26pm

Hi Greg

Off course, the current requirement increases  :(

We could also do 3 in parallel (2/3 lower shunt resistance)  :) but I can't see any benefit of 4 or more in parallel ...

Greg, is that a good idea  :question

ciao

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 29th, 2007, 1:05pm

Hi KL,

You'd have to drive them from a CCS with 1000:1 range . KIS gone. :(

Greg

Title: Re: Simple LDR volume control!
Post by Float on Aug 31st, 2007, 1:27am


Float wrote:
I found the range for fixed series and the ldr series/shunt about the same. :-/
If anything, the fixed series had slightly more range...........


I'm going to retract my comment above, as I've now measured them and found it erroneous.
My fixed series gives about 45db range, and the 'Lightspeed' gives about 50db.
I don't know why it seemed the other way around when I came to my original conclusion.
Apologies if anyone's been misled.  :-[

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 31st, 2007, 6:28am

Hi Float,

That makes sense.

However if we use 27K in the simple resistive version here, 50dB range is achievable and the ground planed PCB shields against hum pickup from the higher impedance.  

When used with the SKpre it may be worth reducing the 100pF styro input capacitor to 33pF - 47pF for greater bandwidth.  :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Oct 17th, 2007, 7:17am

I would like to adapt one of these to my kit built tube pre-amp. I have dual mono 100K pots in shunt mode with 200k of padding  resistor in this pre now-  How would I best go about doing the ldr? Would a wall wart do for the power supply? :question   I'll be feeding it to my GB150D...

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 17th, 2007, 7:39am

Hi sfox32,

Well the supply for the LDRs is independant from signal ground so it's feasible to power it from your tube pre supply just with a dropping resistor.

Do you know the supply voltage it operates on. The LDR circuit draws ~ 13mA.

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Oct 17th, 2007, 9:55am

Yeah, I'll have to check about that..

Title: Re: Simple LDR volume control!
Post by sfox52 on Oct 18th, 2007, 8:05am

OK , the people in the know at the Bottehead forum inform me that there is no current to spare in my Foreplay II pre-amp PS. I could either  use another DC source & bring it in via a jack on the case, Or... I could just try the LDR as a passive pre-amp.. I have a usable case.What sounds like the way to go? I guess if I go with the passive for now I could adapt it  to the tube pre later.

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 18th, 2007, 8:18am

That would have made it easier. :(

You could use a DC plugpack - higher DC volts the better. It draws only 13mA so even a 15VDC plugpack would be running only 200mW. You would just need to adjust the resistor on the LDR board feeding the 5V6 zener. For example, supply would likely be ~ 18V so a 1K instead of the 2K2 provided should do the trick.

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Oct 18th, 2007, 9:01am

Why was I thinking 30 V DC?  Is it15v +/- DC? I have a 15 V dc PS for my Hagerman Bugle that's rated 100ma..I have batteries for the phono pre-amp! Hmmm...

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 18th, 2007, 9:11am

My fault - I've been emphasizing the std setup running from the SKpre , tapping into it's +/-15V onboard reg supplies through a (supplied) 2K2 resistor.

The LED control circuit of the OptiVol (it's been dubbed) runs from a 5V6 zener through a dropping resistor, setting max current at 13mA. And it is floating so makes no internal connection to the signal ground. Obviously this can use any 12V+ DC supply just by resizing the feed resistor to R = (Vs-5.6)/ 0.013. A higher value Vs means a larger resistor value and better filtering though, but it shouldn't be critical.

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Oct 18th, 2007, 9:23am

OK, so if I use my 15+/- DC supply, I can use the supplied resistor?

Title: Re: Simple LDR volume control!
Post by jkeny on Nov 17th, 2007, 12:22am

One thing that I don't think has been addressed in this thread is "How do the LDR's sound" compared to the vol controls you were using previously? Better, worse? After all, this is the main reason for this thread having been started!

I can't give my impressions as life has got in the way of my audio endeavours. So, I'm interested to hear your opinions!

Title: Re: Simple LDR volume control!
Post by KL. on Nov 17th, 2007, 10:46am

Hi John
Greg's SKOptVol is actually better (and cost less) than the passive Ladder Volume switch that I was using  8-)
With Greg now using a 27K series resistor, the minimum volume is -54.5db  :)  
My Speakers are 92db and -54.5db is sufficient for them.

Here's what I wrote a few months ago about Greg's SKPre c/w SKOptVol ...


Quote:
Hi All
I have just completed an SKPre c/w SKOpticalAttenuator and thought that I would give a short report on it.

This is a very transparent and neutral preamp.
The stage is very open, deep and wide.

It is very musical and detailed.  
The highs and mid-range are very detailed and have no edge to them.  
The bass is very detailed and full, also.  
Everything has a very "there" feel to it.  
Nothing seems to stand out or be out of place ... very nice
 
Also, the SKOpicalAttuator is also very good sounding ...  :)


Actually, I would say that Greg's SKOptVol is fantastic and will be my choice of volume pot in the future  8-) :thumbsup

ciao
KL

Title: Re: Simple LDR volume control!
Post by jkeny on Nov 18th, 2007, 8:27am

Thanks KL,
I remember now, reading that review before - glad to see it has gone up in your estimation since.

What do others think? How about you Greg B - how would you evaluate the sonic quality of the LDR vol control?

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 18th, 2007, 10:50am

Hi John,

I'm very happy with the sheer transparency of the Optical attenuator and I'm now using it in my home system.

It's certainly better than the alps blue I had been using.  :thumbsup

Cheers,
Greg

Title: Re: Simple LDR volume control!
Post by iihay on Nov 19th, 2007, 7:37am


jkeny wrote:
Thanks KL,
I remember now, reading that review before - glad to see it has gone up in your estimation since.

What do others think? How about you Greg B - how would you evaluate the sonic quality of the LDR vol control?



It's very nice, I built my SkPre with the LDR incorporated from the start so I can't directly compare. However it is very nice and transparent compared with other vol controls I have heard in the past. Still need to tweak up the resistance to bring my minimum volume down a bit but very happy indeed ;) Beautifully put together module and east to build in as well so  :thumbsup

Iain

Title: Re: Simple LDR volume control!
Post by jkeny on Nov 24th, 2007, 11:11am

Has anybody tried the series/shunt configuration as per GeorgeHiFi, on DIYA, the originator of the LDR vol control? According to him it sounds better than the shunt version. His version is attached

Has anybody been able to compare the two versions? How difficult would it be to convert Greg's OPtivol pcb to series/shunt configuration?

Here's his words:
Quote:
And this was for my Mk I version with a series resistor and just one shunt LDR per channel.
The MK II sounds better than the MK I, and has a much more constant input and output impedance around 7K-10K And it does not have the distortion peak at -6db like the MK I has.



Quote:
I've A/B'ed both with friends, and series/shunt blows shunt away, it's more dynamic (don't ask me why) and sounds tighter and more extended, it does have a much more constant input/output impedance compared to just shunt, maybe, who knows?

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 24th, 2007, 2:27pm

Well he would say that, John.  :)

What's the price - $500?
As Arfur would say "a good little earner". :thumbsup

A good candidate for double blind, IMHO.  ::)

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on Nov 24th, 2007, 7:41pm

I agree Greg, it's good to be cynical of claims of better sonics especially in audio and to look at possible motivations but in this case I believe that we have a genuine claim not based on self interest. After all, he was already selling the Mark I version (the shunt) for a quite good profit margin and he did give this schematic to the DIY community & bring the ldr concept to light.

I may be naive about all this but I wondered as the shunt version seems to be so successful could we not do an experiment as you suggest Greg? How about you Greg, have you got enough matched pairs? You have the golden ears! (and I don't mean golden as in 50 years golden anniversary hehe)

Just some thoughts

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 25th, 2007, 4:32am

Hi John,

Well it is possible down the track a bit.  :)

A few other priorities at present.

Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Feb 1st, 2008, 3:24pm

The Opti-Vol is back in stock!

Been waiting on some NSL units and they came in today so I'm just matching them into pairs right now.

David - don't despair, yours is on it's way! :)

Greg

Title: Re: Simple LDR volume control!
Post by edraket on Mar 22nd, 2008, 6:47am

hi Greg,

Today my Alps blue made place for the Optivol. And yes, it does the job. And how. I'm bl**dy excited.  

Once i'm back on earth i will post my impression, at this moment i'm not in the mood for 'normal' statements. So i'll wait. But right now i had to share my enthousiasm with someone, and i guess it should be you. It is such FUN. And it is MUSIC all over. The fog, the dust, all seemed gone. Yes, i know, in the early days of a loving relationship everything seems perfect. Later on... well, you know the story...  :)  But for the moment i'm very satisfied. Adrenaline all over my body.

Did i made myself clear i like the Optivol? I think the Optivol is Optifun!  

big smile,
Eddy

Title: Re: Simple LDR volume control!
Post by Greg B. on Mar 22nd, 2008, 8:02am

Very similar to my first impression, Eddy!

Good to see the passion of it.  :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by RyanW on Mar 22nd, 2008, 10:15am

I suppose that the Optivol would be the icing on the cake for an SKHeadAmp. Too bad I didn't think of this 2 days ago.

Have you considered posting kits on the price page (ie. Dual reg, LDR volume, and head amp; SKPre, LDR, GB150Dx2, GB300S; etc...) P.S. The new website looks great!

Title: Re: Simple LDR volume control!
Post by Greg B. on Mar 22nd, 2008, 11:29am

Hi RyanW,


Quote:
I suppose that the Optivol would be the icing on the cake for an SKHeadAmp.


Yes I even considered including it at one stage  :)


Quote:
Have you considered posting kits on the price page (ie. Dual reg, LDR volume, and head amp; SKPre, LDR, GB150Dx2, GB300S; etc...) P.S. The new website looks great!


What do you mean? and thanks.

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!


Greg

Title: Re: Simple LDR volume control!
Post by RyanW on Mar 23rd, 2008, 2:24am

Greg,

I mean a complete kit set. People that are less familiar with all of your products may not think to add the dualreg to there Headamp order or they may not consider the benefits of including the LDR with an SKPre. Another example might be a complete Stereo GB150D kitset complete with 2xGB150D, 2xGB150S, 2xSKPre, 2xLDR. Maybe I'm overcomplicating a system that already works well.

Title: Re: Simple LDR volume control!
Post by Greg B. on Mar 24th, 2008, 5:18am

Hi RyanW,

The OPtiVol would work well with the HeadAmp as it has a, without the onboard volume control, a high input impedance currently set at 100K.


Quote:
Another example might be a complete Stereo GB150D kitset


Yes I'm just finalising this now. :)

Greg


Title: Re: Simple LDR volume control!
Post by fierce_freak on Apr 5th, 2008, 10:30am

I just got my Optivol kit and have a few questions.  First, is it ok to mount the alpha pot off-board and run wires from it to the Optivol pcb?  I don't see why it would be a problem, but I like to make sure first.  Also, if I wanted to use an Optivol in a balanced application in the future, would two Optivols both hooked up to a dual-gang alpha pot do the trick?

Thanks :)

Title: Re: Simple LDR volume control!
Post by mastertech2 on Apr 5th, 2008, 3:21pm

hi greg

did you find an ldr with 50 on resistance

if not

have you thought of using two or more in parallel that should bring
the resistance down

i use regular pots but i liked this idea is really cool

if you guys dont mind the complexitiy of it, go for it ,it looks very good controller

cheers

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 5th, 2008, 4:08pm

Hi mastertech2,


Quote:
did you find an ldr with 50 on resistance


Yes I did.  :) They regularly achieve a 'low' of 50 ohms at only 13 mA, and could go easily down below 40 ohms with 20 mA available from the PSU.

They are working very well considering it is such a simple circuit, with excellent feedback from users. :thumbsup

Greg


Title: Re: Simple LDR volume control!
Post by iihay on Apr 5th, 2008, 7:30pm


Greg B. wrote:
They are working very well considering it is such a simple circuit, with excellent feedback from users. :thumbsup

Greg


I second that, working very well for me  :thumbsup

Iain

Title: Re: Simple LDR volume control!
Post by sfox52 on Apr 5th, 2008, 11:06pm

Me Three!  ;)- I shoehorned my Optivol  into a Bottlehead Foreplay Tube linestage pre-amp, powered via a wallwart dc supply. It's the best attenuator I've had in it, including a stepped switch!

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 6th, 2008, 5:21am

Hi fierce_freak,

Sure! You can do that but you can't be sure the first board LDRs will match with the second board LDRs AND you have issues with matching between the gangs of the dual Alpha pot you would use ( which may be insignificant).

The LDRs are selected as an exact match at 1mA or ~ - 26 dB, in pairs, but the spread on individual pairs can be 15% (so far) between lowest and highest so you really need 4 matched LDRs. :o

I was considering making an 8 channel OptiVol running from one single gang Alpha pot, but the chances of finding 8 identical units in lots of 50 is slim so a poor yield. :(

Greg

Title: Re: Simple LDR volume control!
Post by fierce_freak on Apr 8th, 2008, 8:33am

Thanks!  If you do manage to find 4 matching LDR's, please let me know and I will purchase two kits from you.

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 8th, 2008, 8:38am

Hi fierce_freak,

I have 50 pcs of the LED/LDR units arriving within the next few days so should find 4 matching units in that lot. I'll put your name on them. :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by fierce_freak on Apr 8th, 2008, 8:46am

Great, thanks so much!

Title: Re: Simple LDR volume control!
Post by sfox52 on May 2nd, 2008, 7:16am

Hey,Greg! Early in this thread you talked about a remote contol for the OptiVol- did that ever become a kit? As a dedicated couch potato, that seems like a needed item! (Do they have potatoes in OZ?)

Title: Re: Simple LDR volume control!
Post by Greg B. on May 2nd, 2008, 9:28am

Hey sfox52,

The OptiVol uses a 100K pot and I have been trying to source a motorised one for a while. I have a local IR remote kit that will work with this if it has 0.2" (5mm) pin spacing.


Quote:
Do they have potatoes in OZ?)


Spuds? and couches. Couch spuds - my son is one! Glued to sitcoms. He'll watch anything. I told him his brain will turn to jelly (jello if they're of US origin  :)). He seems unconcerned. :(

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on May 2nd, 2008, 10:03am

OK, I'll try searching in this half of the world! As for the boy- I'm sure he'll avoid the jelly(jello)- it seems to me most teens find something along those lines for distraction from the "endless boredom of being!" ( I have a fifteen year old daughter & can relate!)

Title: Re: Simple LDR volume control!
Post by Greg B. on May 2nd, 2008, 11:25am


Quote:
OK, I'll try searching in this half of the world!


Thanks, that'd be good.

Here's the son's other activity - football (soccer).
Current team is unbeaten, but tomorrow may be tough.

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on May 2nd, 2008, 11:30pm

Oh the existential horror of life when you're that age!

As Kurt in Apocalypse Now said " The horror, the horror"

I seem to remember a cheasp motorised pot in Diyparadise - do you know the one?

Title: Re: Simple LDR volume control!
Post by Greg B. on May 3rd, 2008, 5:41am

Yeah - kids!  ::)

Well the OptiVol is proving very popular - I keep running out of these.
More PCBs are on order.

We have a low cost local IR kit but it comes with a 20K pot. We need 100K. It doesn't need any special qualities as it's only varying DC mA.

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on May 3rd, 2008, 7:29am

Well, 100K motorized pots seem pretty rare up our way too.. the stuff I've seen is pricey or not priced. What about a servo & arm rigged to turn a cheap pot? ( Is this getting near Rube Goldberg territory? ;D) I've got an obsolete radio control TX & servos somewhere...

Title: Re: Simple LDR volume control!
Post by Zoxc on May 3rd, 2008, 10:02am

An alternative would be a digital volume control and LED display, which could be combined with some source selector too. It might be some more work and I tend to like potmeters. I keep touching that fancy thing ::)

Title: Re: Simple LDR volume control!
Post by iihay on Aug 9th, 2008, 6:17am

Greg,

Since I built my new speakers my lower volume limit is too high again. I already have a parallel resistor on the optivol I needed before. Is there a way to optimise the resistors needed. Perhaps parallel a variable pot in here, reduce it down and then measure the resistance needed? Any thoughts on this.

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 9th, 2008, 6:53am

Hi Iain,

There are two approaches depending on how much you need to reduce it.

1. Increase the current through the OptiVol. This can be increased to 20mA through the drop resistor. Just (V+-5.6) /0.02 will give you the resistor value. This could gain you maybe 5 - 6 dB.

If you need more, as the OptiVol is doing all it's range of use at the lower end, a divider in front is the answer.  A divider of 6K8 from source and a 3K3 to ground will gain you 10dB. This maintains a ~ 10K input impedance while being a source of -10 dB signal at 3K3 impedance. Keeping it low maintains low noise.

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 9th, 2008, 8:41pm


admin wrote:
Hi Iain,

There are two approaches depending on how much you need to reduce it.

1. Increase the current through the OptiVol. This can be increased to 20mA through the drop resistor. Just (V+-5.6) /0.02 will give you the resistor value. This could gain you maybe 5 - 6 dB.

If you need more, as the OptiVol is doing all it's range of use at the lower end, a divider in front is the answer.  A divider of 6K8 from source and a 3K3 to ground will gain you 10dB. This maintains a ~ 10K input impedance while being a source of -10 dB signal at 3K3 impedance. Keeping it low maintains low noise.

Greg


Ok so 6K8 in the incoming source line to the optivol after my source selector and 3K3 on the equivalent ground sounds easy to implement and low noise.

Not sure how I missed the post at

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!
when reading back through! These values are different so I assume the values you just quotes are optimised for the 27K which is already now in place and standard.

Is this best done on some strip board or direct wiring in source?

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 10th, 2008, 9:46am

Hi Iain,

The 6K8 and 3K3 ( to ground) gives ~ 10 dB reduction while the 9K1 and 1K gives ~ 20 dB cut. Both add to 10K as a load impedance to your source, and keep the nouise and impedance related hum pickup low.

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 10th, 2008, 7:29pm


admin wrote:
Hi Iain,

The 6K8 and 3K3 ( to ground) gives ~ 10 dB reduction while the 9K1 and 1K gives ~ 20 dB cut. Both add to 10K as a load impedance to your source, and keep the nouise and impedance related hum pickup low.

Greg


Ok, I see, should I switch back to 10K before I try this rather than the 27K which is in?

Cheers

Iain

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 11th, 2008, 6:12am

Hi Iain,

No - the 27K is independant of this.

The 9K1 and 1K 20 dB attenuator or the 6K8 and 3K3 one are external and tacked on the front.  

The alternative is to increase the 27K further but we are getting into some large impedances then, e.g. a 20 dB lower gain would need the existing 27K -> 270K. You could try that.  :)  If it doesn't pick up hum then problem solved.

Greg

Title: Re: Simple LDR volume control!
Post by iihay on Aug 11th, 2008, 6:31am


admin wrote:
Hi Iain,

No - the 27K is independant of this.

The 9K1 and 1K 20 dB attenuator or the 6K8 and 3K3 one are external and tacked on the front.  

The alternative is to increase the 27K further but we are getting into some large impedances then, e.g. a 20 dB lower gain would need the existing 27K -> 270K. You could try that.  :)  If it doesn't pick up hum then problem solved.

Greg

Ok starting to make sense now, still not great with the basic theory, good job your kit exists  ;D

Will still a divider in and see how it sounds.

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 11th, 2008, 10:20am

Hi Iain,

I guess I could have suggested to simply increase the existing 27K resistors from the outset, but I was anticipating possible hum and spike ( buzz) pickup with some layouts.  :)

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Aug 19th, 2008, 9:36am

I've developed a balance problem with my Optivol- tracing the input circuit  thru my pre-amp led to the LDR inputs, the left was reading (open) & the right side was around 45K! This was with everything hooked up, but without power. I'm using a 15v +- wallwart for power, it checks fine. Is it possible the left's  LDR's have changed the"off" resistance value? :-/

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 19th, 2008, 11:08am

Hi Scott,

Well it's unlikely I would think. Can you power the OptiVol and measure across the SKpre input with a typical volume setting?

Open sounds like it may possibly be a solder joint . :o

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Aug 20th, 2008, 9:05am

Greg- The resistances track on both sides when it's powered up on the bench- must have been something loose in the connections to the pre-amp. I've reverted to my old dual pots for now. What would I need to do to safely use the Optivol as a passive pre-amp? ( directly to GB150D inputs.) Thanks! Scott

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 20th, 2008, 9:54am

Hi Scott,

Possibly a bad connection.  :-/

To use it as a passive straight into the GB150D input, simply hook the OptiVol output to the input of the GB150D. There is no DC component so no need for a blocking cap.


Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Aug 20th, 2008, 11:21am

Cool! I'm gonna try that! What about a padding resistor- 100k or so? Don't want to scare the neighbors!!

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 20th, 2008, 11:54am

Hi Scott,

If you have no preamp gain stage in circuit the gain will likely be low so you will need to use a higher setting than with (SKpre ~ 14 dB), so I doubt you'll need to pad it down further.

The OptiVol uses a standard 27K at present and typical levels are at -20 dB to -30 dB. There is some room for adjustment of those resistors if needed, but for experimentation, resistance can be added to the incoming signal wire(s).

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Aug 20th, 2008, 11:21pm

Greg- On second thought, I think I'll put the Optivol back in the pre-amp. The imbalance turned out to be in one of the CCS mod boards in there, so I removed all 4 & went back to the standard resistors & 100K pots. I'm sure the LDR setup will be cleaner than the old stock pots are, and I can use those to rig a simple passive attenuator as a back-up to the pre-amp. I do have an old SS pre-amp, but I'm thinking of selling some not needed gear & that would qualify. I'll let you know how it goes. Scott

Title: Re: Simple LDR volume control!
Post by sfox52 on Aug 21st, 2008, 1:59am

Yes!! I've got the Optivol back where it belongs & it sounds sweet!! I've run the gamut, from piano (Diana Krall)& classical guitar Steve Hackett), to jazz( Bela Fleck ), electric blues (Robin Trower) & balls to the wall rock ( Who- Live at Leeds).I don't know how long that problem was there, but I can tell that the one channel was missing the gain the CCS provides,hence the balance difference. Now I can hear what should have been there since I first fired up your amp! The gain of the pre amp is a bit less without the CCS boards in there, but I stayed with 47K pad resistors between the OptiVol & the preamp in- sounds about right. I'll need to order some bits to fix the CCS board, but there's no hurry! Sorry for the false alarm about the LRD's!

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 21st, 2008, 5:41am

No problem Scott.

Good to hear it's working well again. :thumbsup

Let me know if you're needing any bits.

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Aug 22nd, 2008, 6:26am

No worries about the bits for the Pre-amp, I'll get them thru Mouser stateside- I'm gonna listen as -is for a while before doing anything else! Thanks! Scott

Title: Re: Simple LDR volume control!
Post by Gab on Aug 23rd, 2008, 12:36am

Hi, Greg, hi Scott,
I have too the bottlehead3 with the c4board, it makes so much noise into the amp, but i tried straight from the cd player to the ska and it was good but too loud, ill try to put the cd-optivol-ska just for fun.
And ... of course i have a build question, the red led long leg is supposed to be away from c1 is that mean the short leg is nearest to c1 ? meh  :question

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 23rd, 2008, 6:36am

Hi Gab,

That's correct. :thumbsup

The centre center middle hole is for the ground plane to connect to the chassis earth or supply ground, to minimise any hum pickup. Connect a wire from under the PCB for this.


Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Aug 23rd, 2008, 7:49am

Hi, Gab- My Bottlehead is the Foreplay 2 version, for now I have the C4 boards out. I'll try getting them back in there when I find a suitable chassis- it's too crowded in that shoebox! The problems I had arose from moving the boards around & the magnet wire leads separating from the solder points. :o The guys at the Bottlehead forum are always there to help, just like Greg!  Enjoy! Scott

Title: Re: Simple LDR volume control!
Post by mikesnowdon on Aug 30th, 2008, 10:20am

HI Greg,

As you know Im keen on the Optivol. Ive just read through this thread and I have a question.

Does the optivol range start at 0 (innaudible) and come in gradually as you turn up the wick? In other words is the low level control good? I listen to radio at night and it stays on till morning so I need to be able to set low volume easily.

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 30th, 2008, 10:48am

Hi Mike,

The OptiVol, by it's nature, can only reach a non-zero minimum as it is a resistive divider with the take-off fraction being the LDR value to ground. This is widely spec'd as between 30 -50 ohms at full 20mA LED current. We use less (max 13mA) but generally see 50 ohms minimum.

With a series resistor of 27K that means the minimum is

20log (50/27K) = -55 dB while insertion loss is
20log (100/127) = -2 dB with the 100K loading of the SKpre.

So the available range is 53 dB.

If you have high system gain the minimum can be 'soft' in level. If system gain is low it can be < faint. Remember system gain includes speaker efficiency.  :)

Greg

Title: Re: Simple LDR volume control!
Post by mikesnowdon on Aug 30th, 2008, 5:53pm

Cheers mate :thumbsup

Title: Re: Simple LDR volume control!
Post by Dan Giovanni on Sep 9th, 2008, 10:06pm

Hi Greg, I'm thinking the Optivol would be easy to implement as a balanced control - just add a series resistor in the -ve signal line yes?

Dan

Title: Re: Simple LDR volume control!
Post by Greg B. on Sep 10th, 2008, 5:37am

Sure Dan,

Sounds like it would work as it's all floating. :thumbsup

However the load impedance still needs to be high, circa 200K, for the same insertion loss, as there is double the source resistance. Could drop each back to, say, 15K for 100K load.

Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 7th, 2008, 6:51am

I have just reworked the layout of the OPtiVol. The LED is now swapped in position with the zener diode which fits easily under the pot. The now green LED is constant indicating on only, and no longer varies with setting.

On this unit I have measured 42 ohm to 41Kohm with no load, just under 60 dB range, however the max and min values will vary with individual units (NSLs). It could range even higher if I can source a 4.3V zener, but would require higher load buffering.

Current draw is 14mA from a 30V supply.

Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 7th, 2008, 9:18am

With the standard 100K loading of the SKpre the above gives 57 dB control range and 3 dB insertion loss (gain loss).

Greg


Title: Re: Simple LDR volume control!
Post by Dan Giovanni on Oct 9th, 2008, 4:10am


admin wrote:
Sure Dan,

Sounds like it would work as it's all floating. :thumbsup

However the load impedance still needs to be high, circa 200K, for the same insertion loss, as there is double the source resistance. Could drop each back to, say, 15K for 100K load.

Greg



Hi Greg, how would you scale the impedances around a balanced Skpre to avoid excessive insertion loss?

Dan

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 9th, 2008, 5:26am

Hi Dan,

That's a hard one at 5:20 am. :o I'll draw it out later and see.

Greg

Title: Re: Simple LDR volume control!
Post by Dan Giovanni on Oct 9th, 2008, 5:47am

Go back to bed!

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 9th, 2008, 7:41am

OK Dan, awake now. :)

The SKpre in simple balanced mode has an input impedance of only 6.75K, 3K on the -ve leg and 3.75K on the +ve leg. This is just not workable as a balanced load on a floating LDR with an impedance range of 40R to 40K.

The way to go here is to use a balanced buffer between or use two standard SKpre's (100K loading) for one channel, especially if you want to retain a balanced output.

Greg

Title: Re: Simple LDR volume control!
Post by Dan Giovanni on Oct 9th, 2008, 7:52am

Can I not mulitply the 3K and 1K resistors by 10?

Dan

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 9th, 2008, 8:12am

Hi Dan,

Well you could - but you'll need to scale up the 3K and 1K FB resistors as well, which is OK.  :)

Title: Re: Simple LDR volume control!
Post by dinamanu on Oct 18th, 2008, 9:50pm

HI Greg for what we can read on web the shunt resistor do in quality of sound, in the optic to enhanced your optivol I can ad in // an appropriate resistor without vary too much the working range ?

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 19th, 2008, 6:31am

Hi dinamanu,

A resistor across the LDR (shunt component) will limit the dark range and increase the insertion loss.

The SKpre for example, has a 100K input resistor (with the 10K pot removed). I would not want any parallel resistor much less than this.

The OptiVol has a typical range of 40 -> 40K ohms. In parallel with 100K this becomes 40 -> 28K and that's 6dB insertion loss as the series resistor is 27K on the divider.

Greg

Title: Re: Simple LDR volume control!
Post by dinamanu on Oct 29th, 2008, 7:27pm

HI Greg I read a lot near 40page on diyaudio on dlr and are a winner idea  :thumbsup

the full dlr version have different signature , a lot buzz on H2 , some put 100u on led for  self noise ,and a minireg on psu can help the stability of ligth ie better noise .....  

Quote diyaudio :
A/B'ed both with freinds peufeu, and series/shunt blows shunt away, it's more dynamic (don't ask me why) and sounds tighter and more extended, it does have a much more constant input/output impedeance compared to just shunt, maybe, who knows?
----
Actually Mike, if you look at the -5db to -10db level point, which is very close to the level for normal listening with a Red-Book 2v CD source, you will see in the graphs on posts 1008 and 1009, that the series & shunt LDR's are almost at -100db THD, compared to series resistor/shunt LDR which is only at -45db THD.

This is why all my early commercial MK1 (resistor/LDR) Lightspeed Attenuators were recalled and converted to the much perfered better sounding MKII (LDR/LDR) Lightspeed Attenuators, which as a by-product has a more constant input and output impedance compared to the MK1, which CD/DACS and Power-Amps seemed to like better.

So at normal listening levels with CD as the source, you are hearing double the distortion with series resistor/shunt LDR than when Series LDR/Shunt LDR are used, maybe you like the extra 2H distortion in your sound, who knows?


Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 29th, 2008, 8:05pm

Hi Dinamanu,

I'm sure there are differences between my simple OptiVol and the Lightspeed with double the number of LED/LDR units, and 20+ times the price I believe? The OptiVol is matched at around -20dB as a typical listening level (12 o'clock on a typical volume pot) at which any 2HD is lower.

Perhaps I should do one, it would be a good earner. :) Meantime, I'm happy with the OptiVol. It has brought the embodied concept to anyone who can afford an Alps pot, as an alternative. :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by dinamanu on Oct 29th, 2008, 11:13pm

H Geg

you thinks that can  have problem if I the signal are   8Vrms ??


Yes try the double ,I will order a second optivol  ;)

Title: Re: Simple LDR volume control!
Post by dinamanu on Oct 30th, 2008, 7:36am

HI Greg

you thinks that can  have problem if I the signal are  8Vrms ?

H2 ?



Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 30th, 2008, 7:48am

Hi dinamanu,

If you have issues with 2HD at 2V then 8V will be worse. The GB150D amp needs only 1V rms for 100W rms so never reaches these levels and is probably most often run at circa 100mV for 20 dB headroom.

Greg

Title: Re: Simple LDR volume control!
Post by KL. on Oct 31st, 2008, 8:28am


dinamanu wrote:
... if you look at the -5db to -10db level point, which is very close to the level for normal listening with a Red-Book 2v CD source, you will see in the graphs on posts 1008 and 1009, that the series & shunt LDR's are almost at -100db THD, compared to series resistor/shunt LDR which is only at -45db THD.

This is why all my early commercial MK1 (resistor/LDR) Lightspeed Attenuators were recalled and converted to the much perfered better sounding MKII (LDR/LDR) Lightspeed Attenuators, which as a by-product has a more constant input and output impedance compared to the MK1, which CD/DACS and Power-Amps seemed to like better.

So at normal listening levels with CD as the source, you are hearing double the distortion with series resistor/shunt LDR than when Series LDR/Shunt LDR are used, maybe you like the extra 2H distortion in your sound, who knows?


Hi Greg
What's the THD of the OptiVol?


dinamanu, perhaps you could show us the circuits used in the above tests ...



Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 31st, 2008, 8:43am

Hi KL,

I haven't measured it. Maybe when I finish my new soundcard booster I will. I have all the bits now. :)

All this stuff is available on the Silonex website as application info. There's nothing proprietary in either approach.

Greg

Title: Re: Simple LDR volume control!
Post by KL. on Oct 31st, 2008, 10:29am


admin wrote:
Hi KL,

I haven't measured it. Maybe when I finish my new soundcard booster I will. I have all the bits now. :)

All this stuff is available on the Silonex website as application info. There's nothing proprietary in either approach.

Greg

Yeh Greg

It just sounds strange, because an LDR has .1% THD and resistors have miniscule THD. To have an LDR in series with the signal does not make sense ... ???. Greg can you explain what dinamanu is saying?

Title: Re: Simple LDR volume control!
Post by Greg B. on Oct 31st, 2008, 11:45am

nope. Maybe he can.  :)

Title: Re: Simple LDR volume control!
Post by KL. on Oct 31st, 2008, 11:56am


admin wrote:
nope. Maybe he can.  :)


... lets see what measurement your soundcard booster shows :)

Title: Re: Simple LDR volume control!
Post by JoshK on Nov 1st, 2008, 1:51am

So what became of the multi-channel idea?  How about the remote controlled version?  Both MC and RC'd?

I have been wishing for a remote controlled 6+ channel volume control of good quality for years now.   I was sort of hoping something would come of this.  Wishful thinking?

Title: Re: Simple LDR volume control!
Post by Gab on Nov 1st, 2008, 3:08am

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it can also control gain of an amplifier, cool, i wish i had master in electrics ! who knows ?

found nothing relevant on distortion...

Title: Re: Simple LDR volume control!
Post by dinamanu on Nov 1st, 2008, 4:15am

HI kL read well ;) I quote from diyaudio , 154 page....

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Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 1st, 2008, 5:43am

Hi JoshK. Welcome to the forum. :)  

I have 1/2 done a PCB for a 7 channel OptiVol about 6 months back, but was distracted. There is a considerable problem finding closely matched LDRs in 7's, I am lucky to find 4 occasionally for special orders. These devices have a really wide spread and I like to use closely matched pairs. ::)

Hi Gab,

The series resistor/shunt LDR gives very low distortion at the levels I have applied them. Consider:

The input voltage for the GB150D is 1Vrms for 100Wrms. This is sourced from an SKpre with a standard gain of 12 dB (x 4). So it's input is 250mV max. But typical settings of volume are less than -20dB (typ 12 o'clock rotation), indicating a level of typ 25mV across the actual LDR. According to the Silonex website THD of these increases with higher levels and in this application this is very low level in comparison with many intended applications. "Comparable with a stepped attenuator" is one comment that comes to mind. :)

Greg


Title: Re: Simple LDR volume control!
Post by Gab on Nov 1st, 2008, 10:05am

Hi Greg,

Right now I have no way to test my setup properly in small room but i hope to put it in basement once it has carpet and walls and heating, me no want my gear to rust ,  maybe next summer basement job?

If i understand you , if i turn the volume up on the optivol there will be less harmonics... not like i can hear the difference.

Greg do you know how i can filter more my optivol power supply ?, i can add new caps or resistance, unfortunately i don't have like 20M R to put in //, i now supply the opti with 22 volts through the 1K resistor.

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 1st, 2008, 10:17am

Hi Gab,


The 1uF little blue cap is a filter, but you can increase it in value. It only needs to be rated 5V (or more). 10uF or 100uF is fine. :)

Greg

Title: Re: Simple LDR volume control!
Post by Gab on Nov 1st, 2008, 12:50pm

thanks, :) ill put some and listen :)

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 2nd, 2008, 5:35am

Hi Gab,

Just take care to insert the larger polarised caps with the correct opientation. The OptiVol has a + marked to facilitate this, even though the standard 1uF is non-polarised. :)

Greg

Title: Re: Simple LDR volume control!
Post by Gab on Nov 4th, 2008, 12:55am

Yes, :) thanks for the reminder :)

Title: Re: Simple LDR volume control!
Post by dinamanu on Nov 5th, 2008, 6:46am

I Greg can interpret what Pass do ?

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Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 5th, 2008, 7:37am

Hi dinamanu,

Sorry I can't help - I am not a member so cannot follow the conversation without the attachments. :)

Greg

Title: Re: Simple LDR volume control!
Post by dinamanu on Nov 5th, 2008, 7:42am

sorry forgot....

Title: Re: Simple LDR volume control!
Post by dinamanu on Nov 5th, 2008, 7:44am

"And last post of the evening, here's a scope shot of the waveform
and distortion, showing the 3rd harmonic content.
This shows that the element's resistance decreases in response
to waveform voltage. Used as a shunt to ground, this is a
compressive characteristic. Used in series, it has an expansive
characteristic."

expansive/compressive ??

Title: Re: Simple LDR volume control!
Post by dinamanu on Nov 5th, 2008, 7:48am

your optivol feed the B*orbely phono and sound soo good !!!

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 5th, 2008, 8:11am

Hi dinamanu,

OK thanks.


Quote:
your optivol feed the B*orbely phono and sound soo good !!!


It works well with the SKpre as well!  :)  

I think we should not concern with the low order distortion type but more with the fact that it is very low if used in the range of 100 - 200mV, as shown in the graph you posted(again below). This is a typical operating level when feeding a preamp with 12-14 dB gain, then into a typical 26 - 28 dB power amplifier, like an SKpre and GB150D at 10W average level.

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While these 3HD distortions emerge at high levels, they are insignificant at around 200mV.  :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 6th, 2008, 5:11pm

Hi All.

I just want to advise I have ten OptiVol2 kits remaining of the current batch. After that the price will have to rise unless the AU$ gains some 40% in a couple of weeks.  ::) The Silonex NSL Optos come from the US and will cost considerably more in AU$. :(

If you want one, now's the time to order.  :)

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Nov 6th, 2008, 9:30pm

Greg- I have one of the early OptiVol kits ( best upgrade my pre-amp ever had!) What's the difference with the OptiVol2?

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 7th, 2008, 5:01am

Hi sfox52,

The OptiVol2 has a slightly different layout. The (now green) LED is at the rear edge and the zener is in the middle under the pot.

The DC control side circuit is also slightly different - the LED is simply an "on" indicator and does not vary with the volume setting. The zener is 4V7 down from 5V6, and the re-arrangement gives better filtering of the zener noise but that's probably academic (not noticeable). ::)

Greg

Title: Re: Simple LDR volume control!
Post by KL. on Nov 7th, 2008, 6:07am


admin wrote:
Hi All.

I just want to advise I have ten OptiVol2 kits remaining of the current batch. After that the price will have to rise unless the AU$ gains some 40% in a couple of weeks.  ::) The Silonex NSL Optos come from the US and will cost considerably more in AU$. :(

If you want one, now's the time to order.  :)

Greg


I will have 1 thanks Greg (please PM me)

:)

Title: Re: Simple LDR volume control!
Post by dinamanu on Nov 13th, 2008, 1:59am

HI Greg can I powered  the led direcly with minireg ?

4,7v?

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 13th, 2008, 5:09am

Hi dinamanu,

Yes you can... but you will need to take some precautions.

A safe maximum current for the OptiVol is 15mA and the MikiReg can manage 15mA with 20V max Vin-Vout. So you would need to power the MiniReg from less than 25V. :-?

Also the 4V7 500mW zeners I use are only around 4.1V to 4.3V at the currents concerned, so the voltage needs to be set lower and with a current limiting output resistor to ensure the LEDs in the OptiVol are not overpowered.

Greg

Title: Re: Simple LDR volume control!
Post by Greg B. on Nov 25th, 2008, 5:50am

I have just received a fresh delivery of the NSL32SR2's used in the OptiVol and will be measuring and matching them today.

The small increase in price reflects the higher cost of these in AU$ due to it's dramatic fall.  >:(

Anyone with special needs like matched quads let me know as I am likely to find only a couple of quads yield from this lot.

Greg

Title: Re: Simple LDR volume control!
Post by dinamanu on Dec 7th, 2008, 7:12am

:o I have put a tantalum resistor ,WOW

try....

PS my best upgrade!



Title: Re: Simple LDR volume control!
Post by Greg B. on Dec 7th, 2008, 9:21am

Hi dinamanu,

A tantalum resistor hey?  :-?

Where exactly did you put it?

Greg

Title: Re: Simple LDR volume control!
Post by dinamanu on Dec 7th, 2008, 9:33pm

the series 27k(dale) ,but I put 18k Shinkoh , my source can drive 10k

sweet sound but with incredible ambience/reverb  

I don't now if this are only in my system but I thinks  it's worth to try...

hope this helps





Title: Re: Simple LDR volume control!
Post by Milen on Dec 9th, 2008, 12:49am

Hi Dinamamu

yes i agree with your observation, i have good success with 27K tantalum. nice upgrade. what other resistors you tried successfully in that position? ever try metal film type? how bout riken? thx

Title: Re: Simple LDR volume control!
Post by dinamanu on Dec 9th, 2008, 4:53am

HI Milen

nice to see that I'm not crazy ;)

I made a trip only  on Rload of cartidge ,kiwame- riken-dale- shinkoh

same effect but 10 time lower

Next will be nude vishay from texas component

Title: Re: Simple LDR volume control!
Post by Milen on Dec 10th, 2008, 5:13pm

yeah, would like to try the vishay as well but texas component never reply my email. maybe they dont ship overseas.

takman resistor from japan is also recommended to me as well. havent try them yet. just bout to order them. few sites actually has carry this resistor. think of new alternative for shinkoh or tantalum as well as riken which is getting rarer

Title: Re: Simple LDR volume control!
Post by JoeN on Dec 18th, 2008, 11:30pm

Hi Greg,

Do you have any Optivol left for sale?

Joe

Title: Re: Simple LDR volume control!
Post by JoeN on Dec 29th, 2008, 7:55pm

Hi Greg,

I received my OptiVol II kit today, thanks. That was fast service, considering the Christmas break. The matched LDR/LEDs and nice compact PCB are well worth the price.   :)

I will be using the OptiVol to replace a pot on the front end of my Pass JFET preamp, which uses a single +18V / 0V PSU.

Can I feed use the +18V to the V+ hole on the Optivol PCB and the OV to the V- hole? If I can do this, what changes might I need to make to R4, L1, or C1?

On the other hand, can I use a +5.0V regulator to power the OptiVol and what changes would I need to make to R4, L1, C1, or could I just eliminate them?

I have several LM317 based +5V (1.5A) regs on small PCBs left over from upgrades to my CD player and I could use one of them.

Thanks,

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on Dec 30th, 2008, 5:33am

Hi JoeN,

Yes most deliveries have been very quick this year. Santa has a piece-rate contract with Australia Post. :)

You can certainly use the +18V (V+) and 0V (V-) supply, you just need to reduce the onboard dropping resistor from 1K8 to 910 ohms, or 1K. The lower value will give you slightly lower minimum volume.
1/4W is just OK, 1/2W is better.

Greg

Title: Re: Simple LDR volume control!
Post by jm on Jan 4th, 2009, 5:31am

Hi,

I tried the OptiVol without and with the Vbuffer, but in both cases I got a disappointing result with my powered monitors (10 k impedance input)...
I use one optivol for each input (for + and - wires) since I'm in balanced mode.
With the Vbuffer, the result is a bit improved but the output levels remain too low... I was advised to change the 27 K resistor but this will lead to a higher minimum level !
Any suggestion ?
I received 20 Silonex from Allied, please Greg can you explain the procedure to try to match these components ?
TIA for any help !...

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 4th, 2009, 6:10am

Hi jm,

That's no good.  :(

To match the Silonex simply, using a stable and reasonably high voltage supply, say 12V+, run about 100uA through the diode half to ground and read the resistance of the LDR once it settles after about 30 seconds. Then select them in pairs with < 5% difference.

The resistor will be R = [12V -2V] x 10K = 82K for 12V supply.

Greg

Title: Re: Simple LDR volume control!
Post by jm on Jan 4th, 2009, 7:48am

Hi Greg,

You mean 12 V DC ? How to limit the current to 100 µA ?

Cheers,

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 4th, 2009, 8:29am

Yes jm,

12V DC and the resistor value I showed the calculation for. If you have a different DC voltage available just recalculate the resistor using the method shown.

Greg

Title: Re: Simple LDR volume control!
Post by jm on Jan 6th, 2009, 4:18am

Sorry Greg but (12-2)x10 will not equal 82... What's wrong in this calculation ?
Thanks for your help...

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 6th, 2009, 5:40am

Whoops, you're right - 100K is more like it. :)

Greg

Title: Re: Simple LDR volume control!
Post by jm on Jan 6th, 2009, 6:08am

OK,

Now suppose I get 4 NS32SR2S that matched for one resistance value : do you think they will match for all other values or may I try for different values and in this case how many will do ?

What will be the best shunt-series scheme for a balanced stereo attenuator to obtain a wide range from say -72 dB to 0 db ?

May I use the DualReg as the PS for my project or in other words what will be the best PSU in this case ?

Thank you again for your continuous support !...

All My Best,

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 6th, 2009, 7:24am

Hi jm,

Well the NSL's follow a law and that should be consistent over the range. But at 100uA testing, this is middle of the range, a typical operational level. If you can achieve a near perfect match at this level, then it's up to the law to keep them matched at the extremes.

Sure, a series-shunt will give more range as you suggest - good luck with that.  :-? However, if you can achieve typical operating leven in simple shunt mode, at -20dB then there is 35 dB lower or 20 dB higher, workable IMO, but still simple. Not with your 10K load though as the NSL's don't go (consistently) lower than about 40R and your upper limit is 10K. That's 48 dB, not 56 dB.

The DualReg would be fine, but the SKpreReg (to be renamed the LiteReg) may be all you need.

Greg

Title: Re: Simple LDR volume control!
Post by jm on Jan 6th, 2009, 5:22pm

Bonjour Greg !

Thank you for these precisions. Then, must I understand that it'll be difficult to derive a working scheme for a shunt/series configuration ?
Please, how do you calculate the range in dB for given boundaries resistance values ? Same question for the min and max levels...

Have nice dreams ! :)

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 6th, 2009, 7:03pm

Hi jm,

You will need to replace the 27K series resistor (you have tried 10K also I know) with a NSL running an inverse current to the standard shunt one. So when the shunt NSL is supplied with higher current, the series one will have low current and a high impedance.

I think this will only give a wide range with a high impedance buffer, not your 10K powered monitors. So you will need a buffer as well.

To calculate, just divide the impedances. For example 40 /10K =1/250.

dB is 20log (1/250)= -48 dB. If you can achieve 40(min)/100K -> 68 dB - for a 100K buffer. It's a little more complex but that's an indication.

Greg

Title: Re: Simple LDR volume control!
Post by jm on Jan 6th, 2009, 9:50pm

OK ! I think I got it...

I remove the 27 k resistor on each Optivols. I replace them by NSLs (i. e. the resistor par of the LDRs in fact). Then, I feed the LED part of the NSL with an inverted current compared to the current feeding the NSL of the Optivol. Finally the outputs of each Optivol feed the VBuffer... et Voila !

Am I right now ?

If I'm correct, I'll deal with a wider working range and probably an higher output level isn't ?

JM

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 7th, 2009, 4:47am

Hi jm,

Yes tht's what your after. The tricky part will be setting the currents so they go up and down in current via the same volume control.

Too hard for me at 4:45am. :)

Greg

Title: Re: Simple LDR volume control!
Post by jm on Jan 7th, 2009, 5:23am

Bonsoir Greg,

Now all seems much more clear !... Please, do you have a pdf of the schematics of the OptiVol ? Is there any other component to be added when substituting the 27 K resistor by the NSL ?

Merci pour tout ! Fais de Beaux Rźves !... :)

JM

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 7th, 2009, 6:33am

Hi jm,

The OptiVol2 schematic is now included in the guide.

Email me and I will send it to you.  :)

Greg

Title: Re: Simple LDR volume control!
Post by JoeN on Jan 9th, 2009, 6:51pm

Hi Greg,

I have just finished my OptiVol II and installed it on my Pass DIY JFET BOZ. This is a very significant improvement over the current Spence pot. It has more ambience and openness to the sound. Voices, especially female, sound more lifelike and with less of an edge. Bass, just as deep as before, but a little tighter and more easy to follow. Its just sounds more natural than the pot.

The 27k series resistors are just right for my set-up – 15W SE mosfet amp driving Whatmough Monitor speakers – and gives me near silence at the lowest volume.

The next step is to let it all settle and to listen for a while, then try various types of series resistors to see if they make any difference.

Thanks for a nice little project.   :thumbsup

Best wishes.

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 9th, 2009, 7:15pm

Thanks JoeN for the nice 'first take'. :thumbsup

The OptiVol design has only one fixed resistor per channel in the signal path, so is an ideal platform to investigate the sound of various resistors, other than the standard 27K metal film.

Great to hear it's a good fit!  :)

Greg

Title: Re: Simple LDR volume control!
Post by Milen on Jan 11th, 2009, 4:58pm

Hi greg

I just build tube preamp with gain of 6 by using optivol instead of 100k pot. But there's small problem.

Smallest volume is 7oclock. But it reach the listening volume at 8 o'clock. Anyway to do things on optivol so that listening volume at 10 or 11 o'clock? Thx

Title: Re: Simple LDR volume control!
Post by Milen on Jan 12th, 2009, 7:17pm

how bout increasing the resistors in series? Greg? whats your opinion or comment?

whats the diff between the optivol old and new version? are the pcb layout the same? is it possible that i got the new version but i wire it as old version?

Title: Re: Simple LDR volume control!
Post by beebobb on Jan 17th, 2009, 2:21am

Hello Greg,
What changes need to be made to operate the OptiVol in dual mono configuration? Can I simply add another 10K pot and operate each from the same power supply point?

Title: Re: Simple LDR volume control!
Post by beebobb on Jan 23rd, 2009, 12:44am

Hello Greg,
re mono question, I meant can I add a second 100k pot so that each LDR is separately controlled? Would the power supply need any changes? Thanks!

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 23rd, 2009, 8:48am

Hi Milen,

The operation is essentially the same for both - I just reworked the PCB for a more functional layout.

Hi beebobb,

You can run 2 OptiVols for the same power supply if it will deliver 30mA OK. Use 2 100K pots or one dual-gang for the two.

Note edit 10K -> 100K.

Greg

Title: Re: Simple LDR volume control!
Post by beebobb on Jan 24th, 2009, 12:14am

Greg, so in mono each LDR draws up to 15ma and I would have to use a separate voltage dropping resistor and zener for each one? Whereas the OptiVol uses only up to 15 ma total since the 2 LDRs are in series?

The OptiVol I received from you works wonderfully in my Audible Illusions MOD3A. Since I have used the mono pots on my MOD3A for over 10 years and Like the arrangement, I would like to convert the OptiVol to mono.

Title: Re: Simple LDR volume control!
Post by sfox52 on Mar 29th, 2009, 1:26am

I have a possible problem with my Optivol I - I'm losing gain on both channels- I have to turn the pot to 3 or 4 o-clock when 11-12 o-clock used to be the max for solid volume. Should I suspect the power supply first? My Foreplay Pre-amp tends to lose one channel at a time when it acts up- unless the transformer for it has gone south??

Title: Re: Simple LDR volume control!
Post by sfox52 on Mar 29th, 2009, 3:34am

Never mind!! :-[ I should troubleshoot first, then ask for help! It turned out to be a problem with my phono cartridge set-up. I listen to vinyl about 80 % of the time, and I assumed wrongly that the pre or optivol was at fault. Once I tried with CD & all was fine, I went on to check the PS, connections on my Hagerman Bugle Phono pre,(very nice, by the way!) all seemed OK. So I swap cartridges- bingo!! I have a Digitrac stylus installed in my Ortofon OM cartridge, it's made by Ortofon but it fits a bit loosely. The stylus had worked out of the body enough to lower the output! I should remember to start at the source signal before jumping in mid-stream.

Title: Re: Simple LDR volume control!
Post by Greg B. on Mar 29th, 2009, 6:26am

Good to hear you've solved it, Scott!

If the Optivol loses power it increases in volume so would be the opposite of your problem. :-?

Greg

Title: Re: Simple LDR volume control!
Post by sfox52 on Mar 29th, 2009, 11:36am

Thanks for that info, Greg! If that is the problem next time, the neighbors will let me know!- This was a true lesson in the KISS principal!

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 6th, 2009, 5:40am

It was brought to my notice that jkeny has posted my comments (as a quote) on DIYA lightspeed thread in the last day -

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that's fine John. :)

However, in response was -


Quote:
Also the way Greg Ball uses them they are in "shunt" only arrangement with series resistor same as (my MkI) version, which is higher in distortion, maybe that's why he said what he said.


It would seem that the series-shunt topology would have the considerably higher distortion based on the modulation curve as the series element would have the bulk of the signal across it.  :-/

Comparing the two at a typical setting of -20 dB attenuation of the input signal the Optivol has 9/10 of the signal across the 27K metal film resistor and 1/10 across the LDR while in the series -shunt dual LDR, the series element replaces the 27K metal film resistor so the series LDR has 9 times the typ 100-200 mV across it and would produce the higher level of distortion and higher order components accordingly as indicated at the 1 - 2 V intercept of the graph.

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By this assessment the OptiVol would have much lower distortion than the series-shunt method, it's simplicity and lower cost a bonus. The only disadvantage is needing a 100K load for 54 dB control range and 1 dB insertion loss. :-?

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on Apr 6th, 2009, 6:11am

Twas me Greg, apologies for that - I should have checked with you first - email sent.

Your analysis makes sense & greatly favours the Optivol as the low distortion configuration.

Can you say anything about the impedance issues cited as an advantage of the series/shunt configuration (Georges's MKII version)

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 6th, 2009, 6:40am

Heheh. No problem John. :)

I just didn't want to see it bagged. >:(

The series-shunt unit varies the source impedance as well so insertion loss becomes virtually non-existent - so it can give good range of control with lower impedance loading. As far as input impedance being constant I don't know how constant the sum of two oppositely varying LDRs is, but I don't see any great need for constancy. The simple shunt LDR with a 27K input resistor has a minimum 27K at minimum volume and a marginally lighter 30K impedance at a typical -20 dB setting, going higher at extremely high volume settings.

Light loading is a desirable trait quite often. :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on Apr 14th, 2009, 7:20am


admin wrote:
The OptiVol design has only one fixed resistor per channel in the signal path, so is an ideal platform to investigate the sound of various resistors, other than the standard 27K metal film.
Greg


It would be good to hear users experience of different quality resistors for this 27K series R used in the optivol. I'm thinking that something like a Takman would be good to try - reasonable prices Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!


Edit: Some report that if there is a reason for a better sound for a series/shunt LDR it's because the series LDR acts as a high quality R & this can be equally realised by a high quality resistor

Also I wondered what happened to the idea of trying various high quality Rs in the GB150D amp - the ones outside of the GFB loop?

Title: Re: Simple LDR volume control!
Post by Gab on Apr 14th, 2009, 8:08am

Carbon smooth the sound : I don't think they are good. The ones in the kits way better  ;D , I would use PRP instead : they sound different but I can't say they are better than the ones in the kit at same wattage rating.

If your system sounds aggressive (too dynamic) 1 or 2 carbon resistors could help :)

Title: Re: Simple LDR volume control!
Post by Milen on Apr 14th, 2009, 12:12pm

i tried the takman. its metal blue colour one. not the carbon the red colour.

takman blue colour very very nice....  :thumbsup :thumbsup :thumbsup
but tantalum is better tho.

erwin

Title: Re: Simple LDR volume control!
Post by jkeny on Apr 14th, 2009, 4:51pm

For the ultimate, maybe we need a nude Vishay bulk metal foil resistors TX2353 or better TX2575 from Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!



I'm not usually a fan of boutique parts but if there is a definite sonic advantage to a single part replacement then I'm interested. These Rs are about $10 each so sparing use is required!!!!!

What do you guys think - has anybody tried these?

Erwin, you have tried the Takman (blue) as the series R in the Optivol? Can you say what you found?

Title: Re: Simple LDR volume control!
Post by Milen on Apr 14th, 2009, 6:02pm

hi Jkeny

yes i am using the blue coloured takman on my 2nd optivol. its very good. dun know the exact comparison between the stock as i skip the step and straight go to the takman.

from my recollection, i vividly remember that comparing the stock resistor and the tantalum on my 1st of optivol is kind of huge. tantalum has more standout mid (more tube like) while stock is more sterile and more grain and harsh.

lol i just put in my order yesterday for that resistors to texas component. it cost me $10 as well to ship to me in indonesia. beside the 5% paypal fee  :-/

i will try compare this with the takman when it arrive. as it will be replacing the takman if its better

erwin

Title: Re: Simple LDR volume control!
Post by jkeny on Apr 14th, 2009, 6:40pm

erwin,
This is great - looking forward to your review of these resistors - which  ones did you buy TX2353 or TX2575 & what did a 27K cost you?

Title: Re: Simple LDR volume control!
Post by Milen on Apr 14th, 2009, 6:55pm

TX2575 $10.34 each for 27k

erwin

Title: Re: Simple LDR volume control!
Post by jkeny on May 12th, 2009, 7:57am

Any feedback on how these TX resistors sound?

Title: Re: Simple LDR volume control!
Post by Milen on May 12th, 2009, 12:16pm

hi jkenny

i havent got the chance to try on the optivol or gb150. maybe i would try this on gb150 replacing the 27k vishay resistor

but i have tried on my dac. replacing the caddock and takman on i/v resistor and output buffer position respectively.

it sounds a tad more analytical. ie more details. to me there is a veil being remove. but to a small amount. also it has a tendency to sound bright and less natural. so pros and cons. but if you apply them on the right system and right position, it really shine. if you ask me if its worth the money. i would say YES it is. if translate into an amp, its like changing amp. or like changing a capacitor in a tweeter crossover. "IF" this resistor is applied correctly.

havent got the chance to compare to the tantalum tho.

erwin

Title: Re: Simple LDR volume control!
Post by jkeny on May 12th, 2009, 12:37pm

The DAC IV role would be one of the most revealing for any resistor. So in your setup the TX is only a tad more revealing than the Caddock or Takman & then with some brightness alongside.

Doesn't seem to be worth the extra cost compared to these. What price is the caddock & takman?

Title: Re: Simple LDR volume control!
Post by Milen on May 12th, 2009, 12:53pm

hi Jkenny

caddock is around $6 i think and takman around $1.

if about the improvement, someone would pay for thousands of dollars to get the "tad" more improvement by changing amp, cables, pre etc. so its relative to be worth it or not.

in my systems, i would say big resounding YES, as SKA is back in service now  ;D ;D ;D :D :D :D and i like it as it is more natural while having good control and more than enough power than my other amp (which is a tad more revealing and less less less power). As i need that "last last last" details to be audible and SKA can dance it with this DAC i/v resistors changes even without the RCR mod on GB150 PSSR yet.  :thumbsup :thumbsup :thumbsup :thumbsup

erwin

Title: Re: Simple LDR volume control!
Post by jkeny on May 12th, 2009, 1:00pm

I'm sorry, I don't understand - I thought you hadn't tried these TX resistors in the GB150D yet?

Title: Re: Simple LDR volume control!
Post by Milen on May 12th, 2009, 1:01pm

hi Jkenny

yes i havent tried on GB150B, but changing the i/v resistor on DAC also bring an improvement to the systems as a whole.

erwin

Title: Re: Simple LDR volume control!
Post by Stuey on Jun 23rd, 2009, 8:31pm

Monsieur Balle,

Any update on Optivol availability? I'm getting RSI from repeatedly checking the main site.  ;D


Stuey

Title: Re: Simple LDR volume control!
Post by Greg B. on Jun 24th, 2009, 2:16pm

G'day Stuey,

Shouldn't be long. ::) I'm just finishing some PCB artwork for the panels.
I want to get these ordered before the end of June.

Greg

Title: Re: Simple LDR volume control!
Post by TimH on Aug 12th, 2009, 10:31pm

Greg,
are the OptiVol's back in stock?

TimH

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 13th, 2009, 5:56am

Hi TimH,

Short answer is - they would have been had the PCB manufacturer supplied me the full order of boards. As it is I only received a few OptiVol PCBs with which I am just filling back orders.

Is there 'honour' anymore in China or is it 'anything goes' ?  >:(

Greg

Title: Re: Simple LDR volume control!
Post by Abel on Aug 26th, 2009, 6:09pm

Hello Greg,

I've got the Optivol and the LiteReg kits...but, no schematics and list parts to start the assembly.
Can you send me that information ? Thank you.

Title: Re: Simple LDR volume control!
Post by elroy on Sep 16th, 2009, 10:53pm

Im unsure if my OptiVol is working, I haven't hook up any input, Amp etc just powered the OptiVol from one of the SkPre. when turning the pot up/down the LED doesn't seem to change, is this due to no Music input?

Title: Re: Simple LDR volume control!
Post by elroy on Sep 18th, 2009, 6:54pm

anyone?


elroy wrote:
Im unsure if my OptiVol is working, I haven't hook up any input, Amp etc just powered the OptiVol from one of the SkPre. when turning the pot up/down the LED doesn't seem to change, is this due to no Music input?


Title: Re: Simple LDR volume control!
Post by StuH on Sep 19th, 2009, 7:25am

You wont see any change from the led.  Measue the resistence across the pot (optivol out to ground) at various settings, you should get different readings across the range.

Title: Re: Simple LDR volume control!
Post by elroy on Sep 19th, 2009, 7:46am

Thanks StuH.

Title: Re: Simple LDR volume control!
Post by Greg B. on Sep 19th, 2009, 9:02am

Hi Elroy,

The first Optivols had the LED in the control current path andso the light varied with the volume setting - low volume was brightest. The newer OptiVol 2 has the LED in the supply current feed so it has a constant brightness and just acts as a power on indicator.


Greg


Title: Re: Simple LDR volume control!
Post by elroy on Sep 23rd, 2009, 12:22am

Thanks guys. I have since tested both the OptiVol+Skpres and there all working [smiley=2vrolijk_08.gif]

building them was the easy part, now I have to mount them in there boxes. I have the OptiVol+SkPre in one box and the Power/Trans in another.

should both SkPres be connected to the case via a 1N4004-R-1N4004 network or should each Skpre have its own. what about the Optivol straight to the case ground?

Title: Re: Simple LDR volume control!
Post by Greg B. on Sep 23rd, 2009, 8:09am

Hi Elroy,

Good to hear you have it sorted. :thumbsup

If the 2 SKpre channels are both powered from the one plugpack, make sure they have a moderately thick and short ground wire between the two supply grounds (at the point between the large C's is best), and a single R//diode network to case earth.

The OptiVol has a ground plane which is best earthed directly to chassis earth. It is not electrically connected to the circuit.

Greg

Title: Re: Simple LDR volume control!
Post by gungrog on Dec 15th, 2009, 4:37pm

Hi, my first post, what a great site & what cool products!

Anyway, I'm thinking of getting an optivol to replace the 15-year-old ALPS blue pot in my passive pre. I guess I'll also go for the DualSKpreReg to power it.

Now, I currently have a nicely regulated +/- 26vdc available in the amp (driving an input selector relay board) - would this be too much to run into the DualSKpreReg? I see the specs specify a max of +/-24vdc.

Any ideas/suggestions?

Cheers,

Mick

Title: Re: Simple LDR volume control!
Post by Greg B. on Dec 16th, 2009, 2:04pm

Hi Mike,

Thanks. Sorry for the delay, I've been travelling.

Why not power the OptiVol directly from your +/-26V regulated supply. It can use just the +26V and 0V for it's 13A draw. :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by gungrog on Dec 16th, 2009, 4:36pm


admin wrote:
Hi Mike,

Thanks. Sorry for the delay, I've been travelling.

Why not power the OptiVol directly from your +/-26V regulated supply. It can use just the +26V and 0V for it's 13A draw. :thumbsup

Greg


Hi Greg,
No problem, thanks for getting back to me!

So, if I can just use the +26v & 0v then that's great.

I'm guessing the '13A draw' is a typo - 13mA would be more like it.... 8-)

What's the availability like for the optivol? I'll have to leave it till after Xmas now before I can purchase, sadly.

Title: Re: Simple LDR volume control!
Post by Greg B. on Dec 17th, 2009, 4:50am

Hi Mike,

Yes it's a typo. 13mA is right.  ::) ::)

The Optivols will be after Christmas but I hope to ship a few other orders on Monday. It doesn't help that there's a strike in our Australian Postal Service - a govt monopoly and  ::) out of touch with reality. It is now twice the $$ to ship a small parcel to the US as it is the other way.  :o

Greg

Title: Re: Simple LDR volume control!
Post by Stuey on Dec 21st, 2009, 8:59pm


admin wrote:
...Australian Postal Service - a govt monopoly and  ::) out of touch with reality. It is now twice the $$ to ship a small parcel to the US as it is the other way.  :o

Greg


Are you sure about that? I've always found postage from the US exhorbitant, enough to put me off buying some items. A while back I wanted a set of quality cross point screwdrivers (sorta like good 'Jewellers' screwdrivers) for classic camera repair (one of my hobbies) which was going to cost me $25 for postage. I'm sure you know the size and weight of a set of these.

Of course, it could be them gouging, but these are reputable firms.  But, I guess, banks used to be reputable...  >:(

Title: Re: Simple LDR volume control!
Post by jkeny on Jan 29th, 2010, 2:25pm

Greg,
Is there any way to organise the Optivol as a vol control between a Vout DAC (no bias voltage;  2V rms output; min load requirement 5K) into headphones (maybe AKG701s; 56ohm impedance). If not what is the min load the optivol could drive into?  

Title: Re: Simple LDR volume control!
Post by Greg B. on Jan 30th, 2010, 11:36am

Hi John,

The OptiVol will load the source (your Vout DAC) with 27K - a nice light  :) load. However It requires a load itself of 100K+ to give it's rated control range so you would need a buffer, and given the 56 ohm load, you want a quite low impedance output.

You could use a HeadAmp with the volume pot replaced with an OptiVol.

Greg  

Title: Re: Simple LDR volume control!
Post by Greg B. on Feb 4th, 2010, 3:59pm

For all those who have been waiting patiently:

The OptiVol is back in stock! The LDR's have been matched to 1% or better, that's 0.1 dB. :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on Feb 12th, 2010, 7:06am


admin wrote:
Hi John,

The OptiVol will load the source (your Vout DAC) with 27K - a nice light  :) load.
Yes, but this Vout Dac is quite happy directly driving loads down to 16ohm so I was thinking of not putting any series resistor on the optivol input (or just a small one) & using the LDR as a variable shunt to ground. I know this may sound crazy but I've just found confirmation of the idea in the Nuforce uDac using the same ES9022 DAC to drive headphones. This uses no op-amps in the signal path & a volume control on the DAC output. The specified load it will drive is 16ohm to 300ohm.



Quote:
However It requires a load itself of 100K+ to give it's rated control range so you would need a buffer, and given the 56 ohm load, you want a quite low impedance output.

You could use a HeadAmp with the volume pot replaced with an OptiVol.

Greg  

I don't have a schematic or stuffing guide for the original Optivol which I got from you - can you email me one please.

Any suggestions/guiding words about what I'm planning above?

Title: Re: Simple LDR volume control!
Post by Greg B. on Feb 12th, 2010, 7:51am

Hi John,


Quote:
but this Vout Dac is quite happy directly driving loads down to 16ohm so I was thinking of not putting any series resistor on the optivol input & just using the LDR as a variable shunt to ground.


'fraid it won't work  :( - because the Vout DAC's output impedance (matter of ohms) would then become the upper leg of the divider with the LDRs (100K -> 40R) range. The divider could not have a range as it would be:  

Vout = Vin*( 100K -> 40R) / (Z dac + (100K->40R)).

This will always be ~ 1. no range. >:(  Now substitute 27K for Zdac and note the difference.

I'll send a copy of OptiVol1 guide.

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on Feb 12th, 2010, 8:02am

Hmmm, OK, then if I use the LDR as a variable series resistor - any problems with this approach with something like 40ohm full ON resistance?  

Edit: I'm struggling to figure out how NuForce have done it with vol control on this DAC's output driving headphones & no op-amp!

Title: Re: Simple LDR volume control!
Post by Greg B. on Feb 12th, 2010, 8:16am

Hi John,

Yes you could use the LDR as the series element and the 56R headphones as the shunt element. However there are a few limitations:

1. The minimum impedance may be higher than 40R, given the spreads on these, maybe 60R, so signal at maximum volume will be <1/2 what's coming from the DAC ( taking into account it's own Zout) and it may not be enough volume depending on the efficiency of the headphones.

2. The action will be at the extreme low end of the LDR impedance range where the supplied units were not specifically optimised/matched. This is, in normal operation in the OptiVol, the extreme minimum where a dB or more non-tracking is not so important.

Greg

Title: Re: Simple LDR volume control!
Post by jkeny on Feb 12th, 2010, 8:29am

Guess I might have to go with a stepped attenuator for this situation :(

Title: Re: Simple LDR volume control!
Post by Greg B. on Feb 12th, 2010, 8:35am

Hi john,

No harm in trying it though.  :o The stepper approach gives more accuracy in  this configuration though.

Greg

Title: Re: Simple LDR volume control!
Post by JoeN on Mar 22nd, 2010, 9:31pm

Hi Greg,

I have built and used an Opitvol for my Pass Bride of Zen preamp. When I was trawling through the forum just recently I think I recall seeing a comment about a simple two FET buffer that can be used with the Optivol for impedance matching. However, I can't remember where I saw it and the search function didn't find it for me. Can you tell me where I might find the details?

Cheers,

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on Mar 22nd, 2010, 10:14pm

Hi Joe,

I think this could be it -

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This should give better volume control range if your current loading impedance on the OptiVol is less that around 100Kohms.

Greg

Title: Re: Simple LDR volume control!
Post by JoeN on Mar 22nd, 2010, 11:22pm

Thanks Greg,

Yes, that's the one I was thinking of. Rather than hijacking this thread, I will post a couple of questions on the "Simple FET BUffer thread."

Joe

Title: Re: Simple LDR volume control!
Post by lordearl on Apr 10th, 2010, 12:12am

Hi there Greg,

Well after the excellent time I had building the headamp, definitely time to try something else.

If I buy a DC jack, small aluminium chassis, 24v dc 1A plugpack, two rca sockets for input, two rca sockets for output, and your Optivol kit, will I have the ingredients for a volume control that matches the output impedance (22 ohms) of my cd player and the input impedance (100K ohms) of my power amp?

Cheers,
Vaughan

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 10th, 2010, 9:34am

Hi lordearl,

That would work well as a 24V plugpack will output more with the light loading of the OptiVol (only 14mA) depending on it's VA. The smaller the higher as the regulation will be a higher %. You could get 30V dc from a 100mA one loaded at only 14mA. Try to avoid the switching ones though as they are noisy.

The impedances are right for it. However, while the OptiVol is fast and transparent, it is limited in range and you may want a mute button as well, especially if system gain is high and you find yourself favouring the low settings.

BTW The OptiVol can replace the DG pot on the front of the HeadAmp and run from it's +/-15V supply.  :thumbsup

Greg

Title: Re: Simple LDR volume control!
Post by lordearl on Apr 10th, 2010, 1:24pm

OK - but if we do it in conjunction with the headphone amp, we'll need a regulated power supply.

Assuming we can fit the dualreg + headamp + optivol in a chassis,   I'll plan on using a 15V AC plug pack so no need for a transformer.

The following would be okay;
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Or even better, if this is regulated we could be set;
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Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 10th, 2010, 4:16pm

Hi lordearl,

You don't necessarily NEED the DualReg with the pair, but it does give the best results with all chips.

The first supply 15Vac is the one, 17Vac is too high.  :-?

Greg


Title: Re: Simple LDR volume control!
Post by lordearl on Apr 10th, 2010, 10:44pm

OK ace.
Looks like the dualreg is mounted with screws at each corner, and the optical sits on the chassis with the pot, but how would we mount the headamp pcb?

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 11th, 2010, 8:02am

Hi lordearl,

The HeadAmp PCB, being small (50mm x 50mm ~ 2" x 2") is meant to mount off the front panel mounted pot and be located by the panel LED.

Greg

Title: Re: Simple LDR volume control!
Post by lordearl on Apr 11th, 2010, 10:17am

OK got it - but if you were to use the optivol to replace the DG pot, how would you mount the headamp pcb?

Title: Re: Simple LDR volume control!
Post by Greg B. on Apr 11th, 2010, 10:27am

Hi lordearl,

Thanks for that.  :-[

I guess side slot plastic rails glued or screwed to the base. Or maybe a bracket from the heatsink.

Greg

Title: Re: Simple LDR volume control!
Post by lordearl on Apr 11th, 2010, 2:27pm

OK, should not be too hard.

I'll build headamp, with the optivol replacing  the pot, all powered by the dual reg, plugged into an AC 15V plugpack.

Will start a new thread on it once it's underway   :thumbsup

Title: Re: Simple LDR volume control!
Post by mel02 on May 1st, 2010, 8:50pm

Hi Greg:

I am new to this optivol...and sorry don't have time to read all the posts that may answer my questions..

If I use a simple plugpack power supply for the optivol, will it work well too?

secondly, is the music signal going through any other resistors besides the LDR? If yes, which one?

thanks and best regard
Hsu

Title: Re: Simple LDR volume control!
Post by Greg B. on May 1st, 2010, 9:17pm

Hi Hsu,

The OptiVol runs on 4.7V DC internally, dropped down from 24-30V DC in standard form. This is to run from a +/-15V Dc supply consistent with many low level circuits. Because it runs internally from 4.7V Dc the supply dropping resistor can be changed to suit many different DC power supplies. To provide some filtering for quality of DC, it is best to be higher rather than lower, so 30V ( or +/-15V as it is floating relative to the signal ground) is better than 12V DC, but still workable.

There is an additional AC filter inbuilt to remove AC from the control DC, so it is good with even a 12V DC plugpack.

The music signal goes through the input resistor ( 27K metal film 1% 0.6W) and the LDR. This circuit is independant from the DC control circuit. :)

Greg


Title: Re: Simple LDR volume control!
Post by mel02 on May 1st, 2010, 9:25pm

what will be the value for the dropping resistor if I use 12v dc... how to locate this resistor?

my pre has a 12v dc supply...


Does it require  high output(power amp) and low input (source) impedances??

what will be the ideal matching impedances?

thanks

Title: Re: Simple LDR volume control!
Post by Greg B. on May 2nd, 2010, 8:23am

Hi Hsu,

The relevant dropping resistor is R4, directly behind the volume pot. For 30V operation this is 1K8 0.6W rated.

The guide that is provided with the kit details resistor values for other voltages including 12V.  If your preamp has +12V and -12V then it can use this as 24V as it is floating on the DC control side.

The source (input side) impedance is not critical. It will work with low impedances and up to 5K for tube outputs, no problem.

The load impedance can be 50K but best higher at 100K. This gives the highest control range with minimum insertion loss.

Hope that helps.

Greg



Title: Re: Simple LDR volume Control
Post by JoeN on May 1st, 2010, 10:42pm

Hi Greg,

You advised:
Quote:
Does that measure 15V DC? If so, the 1K8 on the OptiVol should be halved roughly.


I am still waiting for the FETs. Futurlec is cheap, has no minimum quantities and shipping is cheap – but it's slow.

I reported that I had I paralleled a 1.5K across the 1.8K for the 0V-15V supply I am using. While I have been waiting for the FETs I have been reading through your Optivol guidelines again and re-reading the Optivol thread and I belatedly note that the supply will accept up to 0V-30V with the 1.8K resistor. I'm a bit of a slow learner and I have only just twigged that the Gainclone has a supply of about +-28.5V (from a 18V-0V-18V transformer)

So, I should be able to remove the 15V regulator and the parallel 1.5K resistor and just connect to +V and 0V 0f the gainclone supply. Is that correct?

The unbuffered Optivol / gainclone combination is proving to be very nice indeed. I am, or at least was, a bit sceptical of the "burn-in" theory, but I note that the this new combination does indeed sound a bit 'sweeter' as time goes by – or am I just getting used to the new sound? The gainclone is new and many in the various gainclone discussion forums mention that their gainclones have taken some time to 'burn-in' and lose that slightly wiry edge that I first noticed.

Cheers,

Joe

Title: Re: OptiVol
Post by Greg B. on May 2nd, 2010, 9:19am

Hi Joe,

I moved your last post to this thread as it has more relevance (to others) here.

Yes, the Optivol will run fine from your available +28.5V to 0V supply using the standard 1K8 0.6W resistor for R4, with one proviso - that it be fairly clean and not bounce around a lot, modulated by the amp output demand.

There are two onboard filters in the OptiVol, for the DC supply: The first is R4 and the 4V7 zener and the second is the series volume pot resistance setting and the 1uF onboard cap, so moderately clean DC sources will be filtered well.

You may want to try filtering the raw +28.5V first, using an RC filter.

Greg


Title: Re: Simple LDR volume control!
Post by JoeN on May 3rd, 2010, 9:40pm

Hi Greg,

I have been tinkering again. Because I want to put the Optivol in the gainclone chassis and power it from the gainclone PSU, I arranged the mains plugs so that both gainclone and Optivol are switched on at the same time.

Normally, the gainclone starts up without any thump, plop, click or sound of any  from the speakers.  However, with the Optivol switching on at the same time, as would happen in the same chassis, I get a rather loud pop from the speakers.

This does not happen when a stepped attenuator is substituted for the Optivol.

I had thought of adding an NE555 timer and relay to shunt the signal, from Optivol to ground at switch. I have used this to shunt a CD player to ground on switch on and it works well. Is this a good idea or is there a better alternative?

I had also thought of using the timer with a relay and switch on the +V line to the Optivol, but if I switch on the Optivol after the gainclone, there is a similar loud pop.

Cheers,

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on May 3rd, 2010, 10:00pm

Hi Joe,

Yes - for sure you will have a pop with the OptiVol switch on as it's an active circuit and needs to settle, and it's right at the input of a x 20 amplifier... probably best to power the OptiVol all the time if possible.
At switch-on it is at full volume and comes down to set level.

Greg

Title: Re: Simple LDR volume control!
Post by JoeN on May 3rd, 2010, 11:44pm

Hi Greg,

Wife Approval Factor means I can't leave electronics switched on. Every thing electronic is switched off after use, not even on standby.

If I use the FET buffer with Optivol, and install a timer and relay to short the output to ground while PS settles, can the buffer sustain the  short to ground after the 47R resistor, or should the resistor be increased in value, say 100R  or is this not a good idea at all.

Cheers,

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on May 4th, 2010, 7:56am

Hi Joe,

I understand.  ::)

It should be no problem for either to have the temp short to ground.
Otherwise, just turn them on first and allow a few seconds to settle.

Greg


Title: Re: Simple LDR volume control!
Post by mel02 on May 5th, 2010, 3:59am

will you ship from Australia or Malaysia... i just ordered the Optivol.

thanks... it  will be fun   :)

Title: Re: Simple LDR volume control!
Post by Greg B. on May 5th, 2010, 7:16am

Hi Hsu,

I have built/tested OptiVols here in Malaysia so I will ship your order from here, later today.

Greg

Title: Re: Simple LDR volume control!
Post by mel02 on May 19th, 2010, 3:14am

hi greg:

"The guide that is provided with the kit details..."

I don't see the guide with the Optivol... I think you have forgot to include it..  will you send it to me via email?

thanks

Title: Re: Simple LDR volume control!
Post by Greg B. on May 19th, 2010, 12:44pm

Hi Mel02,

I always send them by email as the Guide is unnecessary bulk to transport.

Check your email.

greg

Title: Re: Simple LDR volume control!
Post by ianagain on Jun 8th, 2010, 1:10pm

Hmm..Not sure where to post this but There are a lot of posts on optivol and I can't quite get the understandig about its suitability on the SKpre. It seems you consider it a good combination. 8-)
So. the optimum load for the optivol is >,= 100k. The input of SKpre without volume pot is also 100k and a suitable match, right? If the removed pot is only 10k, doesn't it normally overload the input? :-?

Title: Re: Simple LDR volume control!
Post by Greg B. on Jun 8th, 2010, 1:29pm

Hi ianagain,

Yes your analysis is correct, except that the OptiVol is not a load to the SKpre but to the preceding stage - typically a CD player output, where 10K loading (the SKpre pot) is OK. In the case of the OptiVol, it started out as a 10K resistive element but this was quickly raised to 27K for greater control range, so is a lighter load on a CD player or other source than the 10K pot input to the SKpre.

When you speak of loading to a circuit, it is generally at the output - like a speaker, headphone or even the internal feedback network.

Hope that clarifies.  :-/

Greg

Title: Re: Simple LDR volume control!
Post by ianagain on Jun 8th, 2010, 2:21pm

Yes, of course. I should have said "input impedance" of SKpre (at the pot terminals) assuming that is where optivol also connects. dohh.  ::)

Title: Re: Simple LDR volume control!
Post by Milen on May 12th, 2011, 8:47pm

Hi greg

Can you use 2 optivol for balance? And use dual gang 100k pot

Thanks

Erwin

Title: Re: Simple LDR volume control!
Post by Greg B. on May 12th, 2011, 9:40pm

hi Erwin,

I'm sure there is a way that would be possible...the 100K pot would need to be linear and use oppostite halves from the middle setting so one decreases while the other increases.  :-?

Greg

Title: Re: Simple LDR volume control!
Post by nightowl on Jul 22nd, 2011, 6:40pm


jkeny wrote:
Another part VTL5C4/2 (Perkin-Elmer), a dual element optocoupler, may well answer the matching problem of the Silonex parts but gives rise to other issues - it's on resistance is limited to 150ohm which would limit the max vol output, I think. Maybe this isn't a problem?

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!
fanMultimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!
Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register!!


John

:thumbsup

Title: Re: Simple LDR volume control!
Post by amoy on Aug 12th, 2011, 8:17am

Greg B.  How easy, or difficult, is it for a novice to install the OptiVol into an active pre

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 12th, 2011, 8:39am

hi Amoy,

I whould say it it quite simple.:)

Once you remove the existing pot, there are typically 8 wires only to connect to replace the passive volume control in an active preamp.

There are the input L and R wires, the output L and R wires and the L and R ground wires....the 6 connections for the pot function.

In addition there are the +/- power supply wires which are set as default for 30V or +/-15V, but a simple resistor change on the OptiVol board can be adjusted for other voltage supplies.

Mounting of the board is easy as its supported on the pins of the control pot so only needs a small roughly 50mm W x 13mmD space. ;)

Greg




Title: Re: Simple LDR volume control!
Post by amoy on Aug 12th, 2011, 9:12am

OK, then I think I'll be ordering one within the next month, or so - soon as I sort out a few issues. Btw, I'd fired-off a P.M. to you, in the interim, seeking the answers to a few more questions. If I'm being too much of a bother, I apologize.

Title: Re: Simple LDR volume control!
Post by Greg B. on Aug 14th, 2011, 8:40pm

Hi amoy,

It's no problem. :)  Best if you put any technical questions here on the forum so it may assist others with similar issues.

Greg

Title: Re: Simple LDR volume control!
Post by adwsail on Sep 8th, 2011, 1:29am

I'm finally getting around to putting my little TA2020 amp into a box with the Optivol for volume but I cant seem to find a stuffing guide for the board. Any ideas or could someone email me one?

Title: Re: Simple LDR volume control!
Post by Drew on Feb 8th, 2012, 9:44pm

Hey Greg,


Just wondering where these are? Also, with the input impedance, could we possibly set up a second optivol to use as a series function to see the difference in sound? Also looking to use a TX2575 as the input resistor, not too hard to do?
The regs you have, are they a shunt or series reg?

Thanks,

Drew.

Title: Re: Simple LDR volume control!
Post by Greg B. on Feb 9th, 2012, 10:45am

hi Drew,


Quote:
Just wondering where these are?


I don't understand?

Sure can use the TX ..just size issues

The DualReg, Litereg and MiniRegs are all series regs..:)

Greg

Title: Re: Simple LDR volume control!
Post by JoeN on Feb 17th, 2012, 2:31am

Hi Greg,

My Optivol III / FET Buffer combination has been doing very well for more than year, thanks.

However, I am interested in adding an Optivol to the Nelson Pass designed Bride of Zen Mosfet preamp. The design calls for a dual 5K log pot at the output of the preamp.

Would the Optivol with 5K for the input resistors R1 and R2 be suitable? Or is that too easy?

Cheers,

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on Feb 17th, 2012, 4:17pm

Hi JoeN,

The input resistor value of the Optivol has to stay because it's the ratio of the LDR to this that determines the dB of cut and the range of control. A change to 5K would reduce control range by about 15dB.

The easy solution is to put a 6.2K resistor across the Zen output to ground and use theOptiVol in standard form.  The load impedance 'seen' by the Zen would then be the parallel combination 6K2 and 27K  = 5K.

too easy. :)

Title: Re: Simple LDR volume control!
Post by JoeN on Feb 17th, 2012, 10:53pm

Thanks Greg,

I will order a new Opitvol shortly.

Joe

Title: Re: Simple LDR volume control!
Post by JoeN on Mar 13th, 2012, 3:48pm

Hello Greg,

While I am waiting for the Optivol kit to arrive, I built a small PSP to power it. Your specs for the power supply say 0V and +25V to +30V. However, I am getting +31.7V.

Is that acceptable?

One of the issues I am finding in Australia with buying the cheaper imported chinese transformers is that the Vout is usually about 20% higher than claimed.

So when I use a 9V - 0 - 9V trannny with secondaries connected in series, I get 22V instead of the 18V I wanted to keep the PSU within the  24V - 30V spec without having to use a regulator

Not a big deal really but something I have noted.

Cheers,

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on Mar 13th, 2012, 7:58pm

The Chinese manufacturers ever seeking a lower cost production come out with lower regulation transformers which may or may not deliver the goods of Voltage @ current. Smaller cores ( less raw materials) result in lower regulation i.e. higher no  load voltage. This is what you have under no load conditions.

In practice with only 15mA load it should be no problem and is well within operating range.

Greg

Title: Re: Simple LDR volume control!
Post by JoeN on Mar 19th, 2012, 12:32am

Hi Greg,

I installed the new Opitvol in my Pass preamp yesterday with resistors in across signal to ground as suggested. I used 27K Takman brand metal film resistors on the Optivol and 6.2K carbon compositions across the output. The Opitvol replaced a very nice stepped attenuator with Dale MF resistors.

Just for my own amusement, I will probably experiment a little with the 6.2K and see if  Takman or other (audiophile approved??) metal films makes any difference.


There was a distinct and discernible, if subtle, improvement across all aspects of the music. The result was very similar to when I replaced the same stepped attenuator in my JFET buffer preamp with an Optivol. A sense of greater clarity in the music, deeper bass and more defined; a wider sound stage with instruments clealy placed, depending on the quality of the recording / CD being played. If there was any downside, it is that the music seems to be closer to the front than before. But I am not to fussed about that part of the presentation anyway.

Although I don't want to overstate the improvement, I can say that the music is just a bit more enjoyable with the Optivol installed and has been well worth the rather modest outlay for the kit and a small transformer PSU to power it.

Thanks again for your help.

Joe

Title: Re: Simple LDR volume control!
Post by Greg B. on Mar 19th, 2012, 4:12pm

Hi Joe,

Good result  :thumbsup

Thanks for the positive feedback.

Greg

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