I noticed a problem with the DIY Quantussy right after I finished it. Chaos wouldn’t go all the way to zero. There was always a bit of cross modulation in all the oscillators. It was a bit of a head scratcher, because the real Quantussy chaos does shut off the modulations when fully anti-clockwise. The other evening I started thinking about this issue and today I scrutinized the schematics, both Peter’s and mine, and I did find a discrepancy.

Missing Resistor

I found on Peter’s schematic drawing a 100K resistor to ground from the collector of the PNP transistor driving pin 1 of the LM13700 through a 10K. My schematic didn’t have this 100K resistor to ground.

Peter’s schematic shows a 100K (104) resistor to ground.

This resistor is missing from the petal PC board. I went ahead and added it to all five petals.

To my delight and relief, chaos now goes to zero with the red chaos pot turned fully CCW (fully toward +9V).