This effect uses a opto-device,VTL5C3,equvivalent with the CLM6000(Clairex)
This is a single supply unit derived from my rack-tremolo(dual supply)unit.
If you use a guitar with a high output you may get distortion.
Then change the 1Mohm resistor at the input op-amp to 680kohm
Otherwise stay with the 1Mohm resistor.
I've used a 470kohm log pot 'backwards' as DEPHT control to get enough sensitivity.
But a linear pot will probably do, I think!
If you use +15 volts you must change the 27 ohm resistor, below the transistors, to for ex.47 ohm.
Beware of that the maximal current through the led part of the VTL5C3 is only 40mA!
I've burned one all ready!