The core of this DIY VCO is borrowed from the Polivoks VCO, but with an added unique Sync feature to sync the VCO on the rising or falling edge of the input signal. The Syncable VCO is 35mm deep, skiff friendly, and consists of 2 parallel PCBs, doesn't require wiring, has 7 octave switch, and tracks perfectly over 8 octaves.  The Sync edge switch allows the VCO to be locked to either the rising or falling edge of the input wave. This feature has many uses.

As the input sync wave can be of any character and from any source, on arbitrary waves one edge may work better then the other.

Even when wave outputs of a master and slave oscillator are simply mixed together, sync lock edge will determine the resulting shape due to addition or subtraction of different parts of waves. For example, if synced wave is square or saw, and the master is triangle or sine, edge setting will significantly change the timbre of resulting sound due to cancellation or boosting of the fundamental tone. When oscillators are multiplied (ring modulated) together, especially with complex waves, effect of sync edge setting may be even more pronounced, as different (shifted) parts of waves will get multiplied together.

Furthermore, if the sync source wave is a PWM, sync edge setting determines if synchronized slave VCO will lock to the static or moving part of the wave. With dynamic pulse width modulation (especially - fast), slaved VCO pitch will sound different when set to synchronize to the moving part of input PWM.

As with the Polivoks VCO, you can build two VCOs - this is VCO2 with a 2 semitone detune option. In Polivoks synth VCO1 was frequency modulated by VCO2.