CMOS Noise Percussion (CB's DIY Modular Synthesizer)

Published on May 15, 2015 Chris Beckstrom

"Early this morning I built a new module: a CMOS-based metallic noise generator. Inspired by this awesome Hackaday post by Elliot Williams:
http://hackaday.com/2015/04/10/logic-...

A series of 6 40106 square wave oscillators get mashed up with each other through a 4070 quad XOR, and what comes out sounds metallic and noisy and great! I don't really understand what the XOR is doing, but it sounds a lot like ring modulation.

From what I gather this is similar to the analog cymbals on the famous TR-808 drum machine. It even uses the same chip for the oscillators! Who knew you could build it yourself for about $2?

I tweaked the circuit a bit: Instead of a pot for each oscillator, 3 pots control 3 oscillators, 3 oscillators have a fixed frequency, and I added an external input to add additional cacophony (with a switch to go back to 3 oscillators). Soon after installing the module in my synth I realized a running a melodic sequence into that input makes it sound like pitched metallic drums. Cool! Depending on 3 knobs that control the oscillators it can sound like a single tone, cowbell, toms, noise, cymbals, and even dialup-style sounds.

Here is a quick iPhone (and iPhone mic) video of the module in action. I'm running the noise through a low pass gate that is controlled by audio clicks coming out of my computer– a super lo-fi synchronization, but it works. The bass drum and snare are TR-808 samples playing in Ableton Live, everything else is my new CMOS Noise module. This could go great with a bass drum and snare drum module.. Guess I better get back to soldering.

Thanks Elliot Williams @ Hackaday!! What a great circuit."