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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.

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Files
front.jpg
   Front panel design for the Thomas Henry XR VCO
front.jpg
   Front panel design for the Thomas Henry XR VCO
back.jpg
   Picture showing PCB and panel mounted together.
envelope-skew.mp3
   Sample of skew under envelope control.
manual_skew.mp3
   manual sweep of the skew function from sine to octave-up ramp and back.
sync-and-skew.mp3
   sample from Thomas demonstrating the effect of skewing the VCO while it's synced.
sync-no-skew.mp3
   Sample demonstrating the sync function, with no skew involved.
xr2206vco.pdf
   PCB layout by BugBrand For the Thomas Henry XR2206 VCO. Also the Schematics drawn by Bugbrand.
xr_front_panel.pdf
   Front panel design by Thomas henry for the XR VCO.
xr_schem1.pdf
   Schematics for the Thomas Henry XR VCO.
xr_parts_placement.pdf
   Parts placement overlay for the Thomas Henry XR VCO.
Links
http://mypeoplepc.com/members/scott
   Scott Stites website about the Thomas Henry XR VCO. Visit this page for all information about the pr
Manufacturers
Thomas Henry
   Author and teacher
Parts used
1N4148
   High speed Switching Diode
TL074
   Low-Noise JFet-input Operational Amplifier
XR2206
   Monolithic Function Generator
LM394
   4380
LF442
   Dual Low Power JFET Input Operational Amplifier