1U Reverse Sigmoid

A single reverse sigmoid chaos circuit, one of the four in How's the Serenity: an integrator, two all-pass filters and a nonlinear stage with two feedback paths, a much simplified relative of the Mackey-Glass design of the Frisson. Built with any three equal capacitors, it runs as a fast or slow CV source, or as an audio or noise source below 100 nF; 1 uF is a good middle. It works quite differently to the Sloth chaos circuits, with ripples or rolls between each attractor, and its three outputs track each other, delayed by a few seconds on fast builds and by minutes on slow ones. The input expects a positive CV, fed into the first all-pass stage through 10k and a diode; negative CVs do no harm but have no effect.

Key features

• An input, IN, for a positive CV
• Three outputs in gold squares, tracking each other
• Two bipolar 3 mm LEDs
• 6 HP, 1U Intellijel format; Nonlinearcircuits publishes no current draw, depth or assembled price (it sells the DIY PCB and panel)