Runt squealing/oscillating, make it stop!

[Guitarmatt]

I've got a Runt that I'm having trouble with. I built up the pcb and rocked the board successfully. With the circuit working well I started on the enclosure. I got the box all ready and checked the bypass switching before putting the pcb in. Bypass worked fine. Next I mounted the board and secured all pots and switches (I added selectable clipping diodes and switchable ruetz mod). I trimmed the 3 conductor ribbon cable I used for in/ground/out and soldered it to the switch. I didn't install the dc jack yet, I wanted to make sure everything still worked before I did.

Everything doesn't still work.

Even at low low low volumes the pedal now squeals and oscillates. The pitch and volume of the oscillation changes when I turn the knobs. Thinking something might be shorting in the enclosure I loosened the knobs and switches and laid the pcb on the table behind the enclosure. The inputs and outputs are still going through the jacks on the box and the switch, but the pcb is completely free. Tried t again, still same problem.

All I did, knowingly, is shorten the 3 conductor ribbon cable carrying in, ground, and out from about 6 inches to about 1 inch, and then connected the ends to the switch.  On visual inspection the board and my off board mods look just the same as when the circuit was working fine.

Any ideas on how I can fix this situation? I'm going to sleep on it for the night, I could add some pics tomorrow if needed.

[billstein]

Just a thought. When you retired the pots did you get them all back in the right place. The reason I'm saying that is I just had the same problem with an MP jr. I had mixed up two pots, soon as I got that sorted the squealing stopped.

Edit: I saw 3 conductor ribbon cable and automatically thought you had shortened the cable to the pots. My bad.

[gtr2]

I'd try separating the ribbon cable.  Higher gain stuff can cause squeals etc. when when you run parallel wires VERY close to each other.

Josh

[Guitarmatt]

Morning update:

Separating the ribbon cable had no effect, so I started poking around with my continuity probe, found that the output and ground were shorted. I disconnected the board from the switch, and confirmed the prob is on the board, not the switch. Working on it now...

[Guitarmatt]

Alright, the problem is solved with my test rig, let's see if it stays solved when I box it up again.

[Guitarmatt]

Totally fixed! All boxed up and working with my PP+.  The problem appears to have been that when I soldered the in/out/ground leads to the switch, the solder on the pcb end melted and shorted.  Just something to watch out for when you're soldering a really short length of wire I guess, the whole thing will heat up to solder melting temp real quick.