Passive Vactrol VCA

In this module I used a DIY Vactrol to build a voltage-controlled attenuator.

I’ve talked about Vactrols in my Low Pass Filter build. A vactrol is basically an LED and a photoresistor coupled together which would allow us Synth DIYers to control resistance using a voltage source.

In this module, I use vactrols to attenuate volume.

Check out my demo where I use a Vactrol VCA to attenuate audio from one of my square wave oscillators.

Schematics

The build that actually works best for me is a Low Pass Gate setup, which adds a capacitor to the more basic VCA. I found that I get more audio leaks without the cap.

Hope this helps. It’s one of the simplest modules you can make. Let me know if you’ve built it. Tag me on IG @benjiaomodular.