Shown are the schematic and parts list for a voltage controlled clock which I have used in my "Psychtone" and other devices for over two years now. The cost is less than $3, and it is really pretty accurate. The frequency range is about 3 to 25 Hz. with a control voltage range of 1 to 15 volts. I can see no reason why this circuit shouldn't work as an external clock for the 4780 Sequencer by feeding it into the 4780 sync input. This circuit is so much fun to use that I'm sure other readers would enjoy experimenting with it also. Some of the applications include adding syncopation to sequencers, producing square wave vibrato which increases speed as higher frequency notes are played, and as a schmitt trigger (with proper setting of the bias control). If other readers show an interest, I can send some patch diagrams which use this circuit.

Note: PC₁, the bias control may be used to set the initial clock frequency, or set on it's low end (near ground), it adjusts the clock response.

This circuit may be added to the above clock circuit to achieve visual indication of clock rate, and inversion of the clock output pulses.

CORRECTION

It seems that John Mitchell included a few errors in the schematic he sent us for his Voltage Controlled Clock (3/76 Polyphony). The correct schematic for the clock is shown to the right. Also, the unlabeled terminal above the 7404 in the original article should have been labeled "From clock out terminal of IC1".