I need a cheap to build VCA that has a large range of amplification with less concern about the distortion, the main usage is changing feedback strength continuously and such there is little concern about the end shape of the wave i.e. it just has to roughly be there.
However in Spice I am getting this weird clipping that is limiting my maximum attenuation.
Current trough R3 sets the Gain which is visible on the third picture I(R3) along with the output of the differential amplifier (Out1 and Out2), the second image is the Output of the OpAmp that subtracts the DC component of the two outputs from the differential amp.
And while I am at it here are the voltages at the bottom three nets bellow the transistors in order from left to right
Final plot of the output with a 100khz sine wave to better see the gain
it looks pretty good but the distortion is still there
Zoomed in on midpoint
If anyone has better eyes than me and can see why this distortion is happening I would greatly appreciate the info. If not then if you know of a good (Cheap as hell cause I need a lot of these things ~50c/piece) VCA design that has a large MaxGain/MinGain ratio (at least 200x preferably ~1000) then do please tell.