Interestingly enough, the sub oscillator circuit takes up more than half of the waveshaper due to the many options (-1/-2 octaves, saw or square wave).
I’ve tested the circuit with the DCO and got some very nice results. There are still some spikes on the sub saw waves, but while adding filter caps did reduce the spike amplitudes, it also widened their base. I’ve chosen to leave the spikes as is but have left room for the filter caps should I redecide.
The noise board requires four external trimmers - one to center the saw wave, one to trim the triangle and sine waves and two to match the saw wave parts in the sub oscillator.
The noise circuit requires an external noisy 2n3904 or, as in the Andromeda A6, 1N5237B/8.2V zener diode. It has the option of adding a trimmer to control the noise amplitude, but also has room to just use an on-board resistor if exact amplitude is not of essence.
The A6 uses an opamp to offset the noise outputs due to its internal offset center (PMID), which also acts as a filter. This is not included in my circuit.
Here are some photos of the output when the XDCO is connected istead of a function generator:
|Sub oscillator saw, one octave down|
|Sub oscillator saw, two octaves down|
|Sub oscillator square, one octave down|
|Sub oscillator square, two octaves down|