A few posts back I described an experimental VCA, based on the AVDog circuit by Peter Blasser in the Plumbutter. Our friend crucFx (Josh Rodriquez) offered to make a PC board containing four of these circuits. And here it is:

Here’s the crucFx PDF download schematic.

Mido-Centered

As I explained in the former post, many of Peter Blasser’s circuit designs use a single 9 volt power supply (which allows them to be battery powered, too) with a middle (mido) voltage set at 4.5 volts, about which signals swing. The typical peak-to-peak signal voltage is also about 4.5 volts. When used as control voltage, voltages below +4.5V act inversely from those above the mido point. My VCA circuit is adapted from one published by Peter B., as a part of his AVDog module. It expects the incoming signal and control voltages to be mido-centered and the output is also mido-centered. Having DC-coupling lets slow LFOs pass through and be multiplied. The main use I envision is for controlling signal levels, and also for Amplitude Modulation. Whenever an output signal needs coupling to an external zero-volt-based bipolar input, AC-coupling is helpful.

Green jacks are the signal inputs, orange the signal outputs, and violet the CV inputs. Black jack is a zero-volt connection.