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.

 A photo of my Vactrol VCA build

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


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.

 Low pass gate schematics

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.