The Thomas Henry XR VCO

XR-2206 Based Voltage Controlled Oscillator

Courtesy/Thanks to: Thomas Henry

Description: The XR VCO is a voltage controlled oscillator based off of the XR2206 function generator IC. It was designed by Thomas Henry in June of 2006, and is presented here for the enjoyment of all. Feel free to build it, modify it and apply it to any of your DIY projects.

The good stuff: it's a simple circuit, with a lot of bang for the buck/parts count. Thomas really wrung out he chip to get a good feature set for the VCO. The features include:

V/Oct Input
Coarse Tune
Fine Tune
Expo FM Input
Linear FM Input
Sync Input
Pulse Output
Switchable Tri/Ramp or Sine/Rampoid output
Voltage Controlled Skew

One may wonder at that last feature - what is the skew function? Skew provides a method to morph from either a triangle wave to a ramp wave or a sine wave to a 'rampoid' output. Here's the cool thing - it not only morphs the wave shape, but the ramp or rampoid output is at exactly *twice* the frequency of the triangle or sine wave. The effect is an awesome function - putting it under voltage control is quite an experience (it can sound quite filter-like even without a filter). Even at static settings, it can be somewhat like dialing in a sub-oscillator, only, as with most sub-oscillators, the lower frequency is not a pulse wave, but rather a triangle or a sine wave. It really gives some 'bottom' to the sound.