It is a triangle core design using a special type of op-amp called an operational transconductance amplifier (OTA). The VCOs range from approx. 14Hz up to 11kHz, they are quite simple designs with reasonably low drift and can be tuned to 1V/oct (meaning for every 1V change on the CV input the frequency will change by 1 octave, useful if using a keyboard), but they are not exactly rock steady either. There is a trade-off between component quality and design complexity versus drift and accuracy. Anyhoo, the VCOs output triangle, square and pulse waveforms. The pulse width can be set with a pot or controlled by a CV (control voltage). Both VCOs have CV inputs to control pitch, one has a soft sync input, the other has an FM input. Try injecting all kinds of CVs and audio rate signals into these to see what effects you can get.

HP: 14

CV: 1v/Octave input
Sync: Gate in to restart wave for classic sync sound.
PWM: CV for pulsewidth (range settable on back of pcb)
FM: Linear FM +/- 1 Octave? 

TRI: Outputs a triangle waveform
SQR: Outputs a square wave
Pulse: Outputs a square modified by pulse width modulation

Documents for BOM

Document for Build

Document for Schematic

Instructions for calibrating vco here VCO Pot effects, notes PWM pot effects, notes

Known modifications?

Techniques for using this module

Post links to videos or audio showing use, either alone or in featured in patches