The OptiVol is a light coupled stereo volume control based around matched pairs of encapsulated LED/LDR optocouplers. It replaces the conventional ganged stereo volume control like the Alps Blue. It uses an onboard regulated DC supply that is varied by a single pot varying the intensity of the 2 channel LEDs. These, in turn, vary the resistance of the LDRs which form the shunt leg of a potential divider. The unit needs a high load impedance for best results and can achieve over 50 dB volume control range.

These units provide a remarkably transparent and 'fast' sound that belies their simplicity. The unit is fully ground planed for low hum and noise and consumes only 13mA from a DC supply of +/-15V

 

optivol.jpg
 Input Impedance
27Kohms+
 Output Load
100K+ for best range
 Control Range
50 dB+
 Power
+/-15V @ 13mA
 Dimensions
50mmW x 15mmD x 20mmH

DualSKpreReg, a low power dual reg as a standalone item for use on applications up to 50mA but typically in the 10-30mA range and fixed (different resistors for different voltage builds), ideally suited to independantly powering circuits such as the OptiVol, that requires 30V at 14mA. It is a combined 2A discrete bridge, two 2200uF 25V supply storage caps and the two 2 x 300MHz BJT low noise bootstrapped discrete regs. It uses an active Vbe + noise bypassed green LED for reference. The output has 1uF monolithic (ceramic) bypass caps and 2mm hole screw terminal block.

It is all ground planed and may alternatively derive it's power from DC supplies such as power amp supplies, using dropping resistors. AC power can be from a 15Vac plugpack or 30V CT transformer, for +/-15V DC output.

skpre.jpg
 Input
15Vac or 30Vac CT or +/-20V to +/-24V DC.
 Output
+/-15V DC +/-5% at up to 30mA
Regulation
 typ 86 dB to 20KHz.
 Output Z
typ 15mOhm
 Output Impedance
47 ohm (user defined)
 Noise
 < 3uV 20-20KHz Awtd.
 Dimensions 43mm x 51mm