Got around breadboarding a voltage controlled filter for my analog synthesizer finally. The circuit is very simple, it is based on the SSM 2045 integrated circuit I salvaged from half working Siel polysynth. The circuit consists of the filter chip together with some opamp buffering and amplifying to get the signal levels matched with the rest of the modules and with the correct polarity. I still need to breadboard the two voltage controlled amplifier blocks in the circuit.
The operation is very stable and accurate, it’s the usual integrated circuit performance you’d except. The chip has outputs for 2-pole and 4-pole points from the integrator cascade. I really like the 2-pole sound of it. I think I’m going to wire both outputs to the panel with inverted phases so you also get some sort of bandpass output if you sum those together.