I designed a simple dual VCA with AS3360 chip. Basically it’s just two VCAs, but there is also a third output that that sums the other outputs and third CV input, which controls channel 1 directly, but channel 2 as inverted. So, you can put two signals in and with that third CV select which one is coming out from the mixed output. Or put one signal in, as input 1 is normalled to input 2, and use outputs 1 and 2 and use this to pan signal.
My main application for this is to mix two outputs of an oscillator module and/or two separate oscillators. Or this overkill of two #1222s and three of these dual VCA:s to have any combination of both of their square and saw waves. And then a seventh VCA for “normal” VCA function.
Anyway here’s schematic:
And KiCad-files (no gerbers, but you should be able to export them, and remember to add your own funny picture in the middle of the front plate):
I like goblins:
And here’s a video where I ramble about this:
Disclaimer, I haven’t actually build that version 1.0, I did a previous iteration that had couple of bugs that I corrected on the pcb and hopefully fixed properly in the schematic.
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I saw your video yesterday but forgot to leave a comment. Great that you’re on this forum as well. The mixed output and the crossfade / pan CV input are great features and I’m totally going to steal them whenever I make my next VCA.
I see one mistake in the schematic. Those diodes D5, D6 that you want to clip off negative CVs aren’t having any effect because you’re taking the output from the wrong side of the 10k resistor.
PS: It’s nice to see fellow finnish people making synths
Well yeah, that’s a mistake. I’ve built enough distortion pedals that I should know better. Technically I wouldn’t want to have 10k and 100k resistors in series as that would affect the gain. 1k resistor would be within other tolerances of that gain, but then -10 volt CV voltage would have extra 10 mA of current draw. But I really can’t say is that a lot in a larger scheme of things. Or maybe it is if I measured correctly that without input signal this module takes about 40 mA current from the +12V and 25 mA from -12V. So maybe I correct the schematic and change the 100k resistor to 90k?
90k is not a standard resistor value so it might be hard to find. You could replace the 10k with a 22k, and the 100k in the opamp feedback path with a 120k and that would keep the relationship pretty close while using commonly available standard resistor values.
Standard resistor values is something I need to remember to take into consideration. I’ve always had a luxury of a nearby electronics shop that has even all the non-common values.
