The VCO (Voltage Controlled Oscillator) is a component in an analog synthesizer that creates raw waveforms, usually under voltage control to control the pitch (1v/octave at least since the days of R. Moog).
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| Robert"1v/octave" Moog |
These waveforms are basic shapes, like square (or pulse), sawtooth, and triangle, among others, which provide raw material for the rest of the system, such as filters, envelopes etc.
Some waveforms
There are some very nice VCO designs out there on the web, e.g., from Look Mum No Computer and Eddy Bergman.com built around the Curtis CEM3340 VCO chip, or its clone, the Alfa AS3340. The AS3340 data sheet itself has pretty detailed sample schematics.
The VCO i ended up building is deeply indebted to the above designs, with some aspects borrowed from one or the other, and some pieces that i don't care about omitted. I also tweaked some component values to get the pots to yield usable ranges. For example, the range of the pulse width pot didn't even get to 50% (i.e., a standard, plain old square wave) in my first attempt, so i increased the resistors to 5.1M, which allows the pot to cover the range from 0% to 100%.
Here's the stripboard layout (DIYLC file linked below)
I was able to calibrate this pretty accurately with the 10k trimpot. Here are photos of the (almost) finished product:
The front panel is ink-jet printed on adhesive backed vinyl, sprayed with a layer of clear coat (will do a separate post on cutting, drilling, and printing panels).
RESOURCES
- DIYLC File
- Bill of Materials (.xls)
- Panel Design (.pdf, editable in Illustrator)
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