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Step 3: What's a Vacrol?

Picture of What's a Vacrol?

A vacrtol is made from 2 common component, an LED and a Light Dependant Resistor (LDR). The parts are incorporated into one package and face each other. I use heat shrink which seems to work well as a casing.

It’s important that the only light that the photo cell can detect is from the LED. If outside light is able to reach the photo cell, then it will interfere with the performance and sound, that’s why you need to add something like heat shrink to protect them.

When wired-up, the Vactrol acts like a potentiometer - applying a voltage to the Vactrol's LED has the same effect as turning up the knob on the potentiometer. Now if you dim the LED or flash it (like in the Fizzle Loop Synth) and hook it up to a 555 timer, then you can generate different tones and rhythms.

Next I'll go through how to easily make your own vacrol. You will need 2 for this project

michaelo78753 months ago
Check these circuits and 100's more like this in 1980's Forrest Mims III Engineers Note Book published By Radio Shack a Tandy Co. Some times still found on eBay