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