If you’re interested in building an analog synthesizer then the VCO (voltage controlled oscillator) circuit is the best place to start. Oscillators form the core of the instrument, generating basic waveforms which are then shaped and shifted by accompanying components like LFOs, VCAs, and filters and then delivered to our ears as tasty electronic audio candy.
I recently picked up a copy of synth-designer Thomas Henry’s VCO Chip cookbook from SMS Electronics. The 100+ page book covers three chips – the 566, 8038, and XR-2206 function generator. The cookbook covers several recipes for attaining sine, triangle, and square waves from each chip with difficulties ranging from beginner-friendly to advanced-worthy. As a bonus, instructions for some unusual wave-shapers (rampoid, anyone?) and basic test devices are drawn out as well. Most of the plans included are intended for use with a +/-15V power supply. It’s also worth mentioning that the 566 and 8038 IC’s are no longer manufactured but can be purchased via ebay, and several rare/surplus electronics dealers.
I sat down and assembled one of the XR circuits on a breadboard in about an hour. Once I had things powered up and oscillating, I removed the pitch control potentiometer and replaced it with a couple force-sensing resistors which I’d been waiting to put to good use. You can see the scratchtastic results below –
It’s refreshing to have a nice spiral bound manual at the workbench instead of referring to the multitude of webpages and printouts I’d begrudgingly grown used to. I found Henry’s explanations and schematics easy to follow and I plan on using that XR-2206 circuit for a few upcoming projects.