Re: most needed new kit?
Reply #17 - Mar 3rd, 2008, 5:04pm    Hi Brad,  
 
Yes the HeadAmp is done and 'locked in' . It's a chip driven (OPA2134 std) with LED bias and BD139/BD140 outputs with either Class AB bias or full Class A. The chip is biassed into Class A irrespective. Unlike the cheapies, it is fully ground planed for low stray noise pickup and good shielding.  
 
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It might even be a good project for those new to the hobby.  
 
Yes, it's very simple - low parts count and only needing input, output and supply wires. It delivers very low distortion and could also be used as a stereo line stage preamp with high current drive.  
 
Greg  
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Re: Switch with soft start
Reply #8 - Mar 3rd, 2008, 3:40pm    Hi Brad,  
 
HeadAmp should be 3 weeks ETA!   It will be ~ 2" square and either low power Class AB or full Class A and VERY clean and extended, with onboard volume control and socketed chip to enable chip rolling.  
 
It will drive all 32 ohm+ cans to deafening levels.  
 
Greg
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Hi Greg,

Which type/brand of headphone-jack would you like to see used with your new HeadAmp kit?  
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Your DualReg psu has yet another use.  

BTW, your idea to use a socket to enable easy chip rolling was/is superb!   What alternative chips do you see as 'prospects' for the chip rolling option??

Cheers,
Brad

Hi RyanW,

I don't think there's any need for a switched HP jack except for portable use where it can switch off batteries when the plug is removed.

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Yes. There was no way I could fit half-decent 100mA discrete regs onto the board so that's ideal. Not sure the HeadAmp price yet, but -

I will do an introductory offer for these of AU$100 + $10 p&p for the pair!

I'll supply it with either a TSH22IN (ST micro) or OPA2134 (TI).  The immediate target for chip rolling would have to be the LM4562, particularly for non regulated (battery powered) portable use.

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minimum would be 10VA but, due to the poor regulation of these in general, I would opt for 20VA 15-0-15 or 2 x 15Vac.

Greg

Hey Greg,

How would your design do when driving a 62ohm load? I have a pair of AKG K701 cans and they well known for being slightly problematic to drive correctly with some head amps.

At the moment I have them running through the headphone output on an EMU 1820m interface. It works and sounds OK but I've heard them through a Graham Slee Solo and there's clearly something missing from what I have now. The drive and bass is light in comparison. I've been told this is a sure sign of a struggling headphone output.

How long until this is ready to buy and will you offer a finished version in a nice compact and unfussy case? Does it share the GB sonics?

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Cheers Greg. That's good to hear then.

I'd go with your introductory offer of $100 and have the regulated supply included. How long until these are available to buy?

I suppose I had better start saving if I want to take advantage of the introductory offer.