VCA using DIY LED and LDR Optocoupler, on Breadboard (with schematic)

The circuit on breadboard is a VCA, using our homemade optocoupler. It is basically the same VCA circuit found at Roland GR-300 guitar synthesizer outputs, just with higher audio input impedance. The resistance range of the optocoupler LDR here is from 10M to 2K ohm, with a control voltage from 0 to 10V. The LDR is placed at the input of an inverting amplifier, so, when the control voltage is 0, the LED will be at minimum brightness, and the LDR will reach its maximum resistance (~10M). This reduces the inverting amp gain by a factor of 418. A 10Vpp audio input signal is attenuated to a 24mVpp output signal. Maybe enough for most applications, but surely not for all.

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