I’ve built the AI Synthesis LPG, putting it behind a Kosmo front panel — no (intentional) changes other than three of the pots and all the jacks are panel mounted and wired to the footprints on the PCB.
It kinda sorta works. But the depth switch has me baffled. Even with the depth knob turned all the way down, flipping the depth switch causes the amplitude (in VCA mode) or the cutoff frequency (in VCF mode) to decrease significantly. For instance at one point I had it in VCF mode, with the resonance turned up to self oscillation, and flipping the depth switch changed the frequency from 420 Hz to 160 Hz. The maximum amplitude or frequency with the depth switch on is low enough that I don’t consider the depth switch really usable.
Trying to investigate this, I did an LTSPICE simulation of the CV handling part of the circuit — and it seemed to behave consistently with what I was seeing; it showed a big decrease in the vactrol LED current with the depth switch on, even with the pot at maximum resistance.
Then I tried breadboarding the CV part of the circuit — and it too behaves in the same way.
“So that’s how it works”, right? No, because Abe (@AI-Synthesis) says with the knob turned down, the depth switch should not cause any change — and he sent me a video clearly demonstrating that on his module.
This is driving me nuts. I’ve checked my components, they’re correct. Checked connections, haven’t found any wrong. Measured resistances, they’re what you’d expect. Module, breadboard, and simulation are all in agreement and all, evidently, wrong. Abe hasn’t been able to come up with any explanation either.
Anyone here have any thoughts? Anyone built the AI LPG, or a similar design with depth switch; does yours behave like mine or like Abe’s?