The sub oscillator was one of the first synthesizer modules Ken Stone ever built, back around 1980. The first version was designed with the ETI 4600 in mind, and was published as a circuit idea in the Australian edition of ETI.

Another circuit he used at the time to "fatten up" the sound of his single oscillator synth was a "harmony generator", achieved by running a 4017 decade counter chip wired to divide by three or six.

The CGS701 combines both of these circuits, giving a two channel sub oscillator, which allows each channel to be used independently, or driven from the same oscillator, but set to different intervals. As a bonus, both channels can be multiplied or "digitally ring modulated" giving even more effects. Inverted [!A] and [!B] outputs are also available and will generate negative voltages.

Some ideas on how to use this module:

Fed by two VCO's it can operate as two independant sub-oscillators:-

1. Set [PRESCALE] to [BYPASS],
2. select [SUB] and set [B MODE] to "=B" (switch out),
3. Connect your 2x VCO's to the inputs [A] and [B],
4. Take your outputs from the [A]/[!A] and [B]/[!B] as desired,
5. Adjust the [A MIXER] controls for the [A]/[!A] output and the [B MIXER] controls for the [B]/[!B] output. [n/1] is the original signal, [n/2] is that signal 1 octave lower, [n/3] is the original signal 2 octaves lower and [n/4] is the original signal 3 octaves lower.

A ring modulated output can be obtained from [B]/[!B] by setting [B MODE] to [B*A].

Running both sub-oscillators from the same VCO, tuned to a fifth over the base note you require, and with the [PRESCALE] set to divide by [3], it is possible to create harmonies. An unusual effect here is that the ring modulated outputs [B]/[!B] give a fatter chord-like sound that remains independant of minor or major scales, allowing "one finger chords" which can be handy when used with a related sequencer driven bass line.

Careful mixing of the ring modulated output [B]/[!B] with the other channel's divided output [A]/[!A] results in some interesting sounds, especially if one of the channels is being driven from a low frequency oscillator. Running like this, it could be considered to be a "harmonic sequencer"

Running both inputs from the same LFO/clock signal, and feeding the mixed output into the 1V/oct input of a VCO gives you a pattern based sequencer, where the prescaler, ring modulated outputs, etc., all have a bearing on the pattern. Quite interesting patterns can be created this way. Each knob of course varies part of the overall structure, instead of a single note as per a regular step sequencer.

Build Guide