More modular breadboard experiments

I added a pair of low pass voltage controlled filters and a pair of voltage controlled amplifiers. The filters are Sallen Key filters and the cutoff frequency is controlled by modulating a pair of vactrols (the large black components near the middle of the board), The VCAs are based on a circuit using a transconductance op-amp (OTA) called the LM13700.

I later adjusted the two circuits (after making the following videos) as the filters weren’t reaching the higher frequency spectrum (I sacrificed a little fatness for a better sweep range) and I improved the signal to noise ratio of the VCA.

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