VCF/VCA based on the Korg MS-10
The MA35 is an internally-coupled VCF and VCA based largely on the back end of the legendary Korg MS-10. The VCF section is based on the classic Korg-35 filter architecture, implemented using discrete transistors rather than the original (and impossible to find) proprietary ICs.
Unlike the original it is switchable between Lowpass and Highpass modes of operation, which can either be done manually using the toggle switch or with CV via the "mode" jack. There is also a two-channel audio mixer built in to the input. Modular-level signals will overdrive the inputs as you pass ~12:00 on the dial — stay below this threshold for a smooth, liquid sound or push past it for fuzzy screaming mayhem! The VCA section is based on the MS-10's "single-transistor" design, which adds distinct color to the sound and is an important part of capturing the spirit of the original.
Care has been taken in the selection of period transistors and opamp chips to keep the character of the sound as authentic as possible. This is not a hi-fi module! It's a little raw and a little noisy, in all of the very best ways.
The MA35 is fully protected from reverse power connection. The proper orientation of the ribbon cable is indicated on the top copper layer of the PCB, just below the power header.