VCA-1A:

Dual MS20 VCA - scratch built

This was the first VCA I ever built. It's based on the Korg MS-20 VCA which uses transistors for gain control and an opamp buffer at the output. CV feedtrough is a bit of a problem with this design - it thumps with quick CV changes

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VCA-2A:

3080 VCA - design by Thomas Henry

This VCA was scratch-built on Radioshack pad-per-hole board. It's wired almost exactly as shown in The Electronic Drum Cookbook by Thomas Henry, and it's based on the now obsolete CA3080. Thomas explains that this is a no-frills VCA that is probably only suitable for percussion. I found it to work quite well, even for synth sounds, although it thumps a bit with fast CV changes. I think redesigning the CV path and adding a few trimmers would be a good help. Since the 3080 is now obsolete, I'll probably never experiment much further with this design.

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VCA-3B:

Dual 13700 linear VCA - design by Paia

After the CA3080 went obsolete, I began looking for a simple VCA circuit to replace the design used for VCA-2A. Both the NJM13600 and NJM13700 are still available from New Japan Radio, so I thought they would be good OTAs for experimentation. I drew a circuit board of a dual VCA, with the design taken from the Paia Fatman (although the fatman only has a single VCA). You may download the schematic for VCA-3B here. Please note that the board layout is a component side view, not a solder-side view.

I'm quite happy with the results: Quiet operation and acceptable CV feed-through. I may decide to revisit this design later an add a 2 transistor expo converter, and perhaps add adjustable make-up gain on the output buffer.

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VCA-5B:

AC/DC VCA with mixer - design by EFM

VCA5B is built on a circuit board that I bought from EFM. It's a single VCA with both AC and DC inputs and outputs. It also has a built in inverter and a mixer. It's an incredibly handy module, actually. The VCA-5B schematics are avaialble here. You may also download a copy of my faceplate design and the corresponding drill template.

I still have an unfinished VCA-5B in my workshop. I created a second variation of the faceplate design and drill template that make the mixer more predominant with added volume controls. This is the design I intend to use for my second board.

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