TS9 - no sound, only hum, after clipping diode mod

[the_stinking_killer]

hey all

Was modding a TS9 for a friend of mine today. Tube was working all along, even with the modded circuit (very simple mod: jumped two wires from the clipping diode section to a dpdt to switch between 4148s and some germaniums I picked up on ebay).

Once I had the mod working and sounding juicy, I drilled the box for the new switch and installed everything. Stomped the footswitch, and...bbbbbbuuuuuuzzzzzzzzzzzzzzz. It's present on both bypass and with the effect on, but much louder with the effect on. Drive, tone, and volume all change the sound of the buzz, so I know it's in the circuit somewhere. Very frustrating, as nothing changed, as far as I could tell.

Potential causes: I'm using a crap Radio Shack PS (or should I say POS? Haha) with variable voltage. It is definitely noisey, but the pedal was working fine with it earlier. Also, I had it set to 12V from an earlier project, but it had been working with that as well, and I know this circuit should be able to tolerate that voltage.

There were no funny smells, no pops, nothing. All the electrolytic caps look/smell fine.

I'm flummoxed. No idea what changed since I drilled the enclosure. I'm assuming it's a short somewhere, but again, it was working out of the box.

So, where should I start? Initial diode? Transistors? Op amp (it's not the 4558, it's one of the other ones; I do have some 4558s, though, and I'm thinking I may just bite the bullet and socket the thing if I'm gonna have to take it out anyway)? There is one cap that's reading 9V on one leg and around 200mv on the other; perhaps that's the culprit?

Thanks for any help; you guys are the best. I'll report back if I get to the bottom of it myself. I may just bust out some vero and rebuild the darn thing, haha. Not too complex a circuit...

[J0K3RX]

Sounds like a short to ground. See if when you put it back together no bare wires from the switch or the lugs from the back of the switch are touching anything with the pedal closed up..

[GibsonGM]

+1 
The other big thing that can make that horrible sound is if you DON'T have a ground connected. Like, if you output jack, or input jack, are not connected to ground on their sleeves.  Nasty!   

Present in bypass AND engaged makes me think it's something like input ground missing or something like that.   Then it gets amplified inside the effect.

Like Jok3RX said, just go in there and eyeball everything, this is very common!   And welcome to the forum

[PBE6]

One other possibility, the wires connecting the PCB to the controls can sometimes come loose when flipping the board around during modifications. If nothing else works, try reflowing the solder at the connection points on the board - all of them, even if they look fine.