A Plague of Demons

A thru-zero VCO: analogue switches (DG202 or equivalents) achieve the thru-zero function, after ideas in Electronotes EN#75, themselves based on suggestions by Bob Moog. FREQ is a fine tune to set the module up for phase reversal, and the LEDs show when it happens. With nothing patched into the CV input, the CV knob is a tuning knob for higher frequency operation; with a CV patched in, it attenuates it, summed with 1V/OCT. SELF CONTROL feeds the sine output back into the frequency modulation sub-circuit (turn DEPTH up for it to act, or better, use a CV on FM ENV). SAW and PULSE are both controlled by PW and the PWM input: PULSE has its width varied, SAW becomes chopped and morphs into a complex, harmonically rich waveform, its frequency eventually doubling. SINE and its inverted form (SINE+180), TRI, SAW, PULSE and SQUARE out.

Key features

• 1V/OCT, FM ENV, CV, PWM and EXT MOD in
• SINE, SINE+180, TRI, SAW, PULSE and SQUARE out
• FREQ, SELF CONTROL, DEPTH, FM ENV, PW, EXT MOD, CV and PWM knobs; two LEDs, ← and →, showing phase reversal
• 12 HP; Nonlinearcircuits publishes no current draw, depth or assembled price (it sells the DIY PCB and panel), and ModularGrid lists none