Another Dual Voltage Controlled AmplifierBack to "Music From Outer Space" Analog Synth Pages
The function of this dual VCA is very similar to the other one. It uses one less chip but one more transistor. It uses the built in LM13700 buffers instead of OP-AMPs. You can never have enough VCAs so build build build... I built the circuit board and it works perfectly. I am using about + and - 4 to 5 volts signal in. You can use a higher level of signal in BUT you need to increase R17 (and R37) proportionally. That is, if you want to use + and - 8 to 10 V signals then double the value of R17 (and R37), etc. The CV Offset adjust pot should be panel mounted. Its purpose is to offset whatever control voltage you are using to control the VCA. I have noticed that for control signals that are operating about ground (i.e. + and - 4 to 5 volts) the pot is usually toward the left when set to linear response and usually toward the right when set to exponential response. I changed the CV offset adjust pot to be connected to -12V instead of ground because I found I needed that much offset adjustment when driving the CV with 0 to 10 volt control voltage sources. You can overdrive this so watch your signal level and the setting of CV Offset adjust R1 (and R21). Of course overdriving it produces some interesting timbres... so experiment. I built 2 of these boards (resulting in four VCAs) into one module and it rocks.
Another Dual VCA Schematic (pg. 1)Schematic Image generated by RJWSoft's Schematic Publisher software
Another Dual VCA Schematic (pg. 2)
Another Dual VCA PC Layout (Parts Side View)
Another Dual VCA Parts Placement
Another Dual VCA Response
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