Hello synth people, i need help with this
this is the VCA stage of my wavefolder
it’s purpose is to scale the incoming signal in a way where at maximum it’s going to provide maximum fold
and at the minimum it’s going to make the circuit act as a passthrough or bypass
the design uses a vactrol to vary the gain of an inverting amplifier
there’s also a LED driver circuit to control the current going through the LED and thus its brightness
At maximum LED brightness, we have lowest LDR resistance and thus the input resistance of the amp is equal to the feedback. Resulting in Gain = 1.
The maximum gain in this circuit is meant to be 1
that’s the maximum fold setting
For the minimum gain, that’s an arbitrary value, if we allow the LDR to be in complete darkness, it’s resistance will tend to 2 ~ mega ohms which will make the overall circuit not a passthrough/bypass, but an atenuator.
So i need to be able to set a minimum gain that’s mapped to the lowest input voltage which is 0 (in order to not invalidate part of the potentiometer’s range)
Since every vactrol is unique, i need a way to set these maximums and minimums for each voice board
A way to set this gain 1 condition is to have a trimmer potentiometer as feedback resistance in the U1 opamp and match it to the equivalent input resistance when the LDR is at its lowest resistance (maximum LED resistance).
I need to find a way to set the minimum gain
any suggestions?
obs: that 3M resistor in parallel with the LDR was my previous attempt at setting this lower boundary.