LM13700 VCA help

Hey I recently built this simple LM13700 based VCA and got it to work for the most part. The problem with it is that instead of opening up the audio signal when the gate signal goes through, it basically closes. In other words, whenever the audio is going through and a gate signal hits it, it closes. I’m not sure if this is what it’s actually supposed to do or I did something wrong with it, I will link the video and schematic to it, would anyone be able to help?
(Dropbox - Schematic_13700-Dual-VCA.pdf - Simplify your life)
13700 Based Dual VCA - Modular in a Week 2.3 - YouTube

With 0 V on the CV input you should get no output, and with a large enough positive CV (probably +5 V) you should get basically full output. If that’s not what’s happening, there’s something wrong.

Update: I actually found the same issue on the forms here and it’s just the circuit itself that’s the problem, and it really isn’t the best vca to make

@dud has had success with this one

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If that’s not what’s happening, there’s something wrong.

I’m not sure how that circuit can even work (EDIT: with reasonable CV signals), since the IABC input is current driven and for the LM13700 the reference voltage is two diode drops above the negative rail, not 0 V. See the discussion here:


My simple LM13700 VCA looks like this:

It’s not perfect but it works, it’s in my DIY synth. You may want to adjust R7/R14 for your final gain, mine’s pretty hot, something like 16V peak to peak.