Build Your Own Clone Message Board

So I've built my Li'l Comp, and I've gotten it to work. I am going to look over all the parts and check for placement errors, and check that all solders are good, but I wanted to fire off this question first. I managed to reverse the negative and positive from the power supply the first time I tried the pedal. Nothing happened. Could this have damaged something?

The issue I'm having is that if I let a note sustain, by a time when it has a certain low volume, the note kind of pinches. It goes kind of "swump" to try to be as correct onomatopoeic as I can. It gets a certain buzzing to the note and it dies of rather quickly and abruptly. If I continue to play very softly, the buzzing persists, but the moment I hit a string a bit harder, it jolts it back into what seems like the correct manner. It takes less to get this to happen on higher frequencies, and notes sustain longer on lower frequencies before this happens. This makes me think of some capacitor as a part of a filter being involved, but I'm just guessing.

There's also some static when I turn the sensitivity knob, and the position of the sensitivity knob affects the issue. Thanks for all input!

Certainly sounds like unusual behaviour. You seem to have some good ideas with troubleshooting. Electrolytics around the power supply and the diode are where I'd check first.
Of course photos always help if your first attempt doesn't pan out

Hooking up the power supply with reversed polarity may have damaged the 3080 chip. I would start by replacing it.

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"It’s your soldering."