Replaced all pots, now amp volume seems quite a bit lower

[professormudd]

I ended up with some oscillations in OD due to the leads being to close between the first stage and the second, I ended up swapping the triode sides on V1 so that V1's first input was farther away from the V2 OD tube, This could be similar behavior you weren't getting when it wasn't working as optimally? Try at a minimum carefully putting some kind of grounded shield between V1/V2 and see if that does anything. Just don't touch the anodes or you can create a disaster.

~Phil

BLUF: Improvement, but still gremlins. I am going to be pretty verbose in case anyone else has similar problems in the future and stumble upon this thread.

I feel like I might have accidentally turned my OD channel into a Theremin for a while there. I was sweeping the input volume and it totally sounded like an electronic slide whistle. I thought the mothership might come land.

I did a quick shield test like you mentioned and it did help me resolve some issues, but not directly.

I took a small piece of metal the size of a baseball card with an alligator-clipped lead to ground, held it with plastic tongs, and tested holding it in various positions to shield things. At one point I bumped one of the eq leads and the noise changed drastically in pitch. I tapped the wires connected to the bass pot and it was almost musical the way the noise changed pitch. Almost.

I am still very new to understanding signal paths and how amplifiers work, so it took me taking what little I know about pots and following each wire and guessing whether or not signal was going one direction or the other to figure out what might be going on.

I took a bamboo skewer and gently started moving the leads around near the bass pot and I was able to silence the Theremin tones momentarily when I tapped on the wires. I isolated the cause to be the shielded cable ground from pin 3 of the drive pot. I ran the skewer between them and the noise halted. As ChopSauce had warned, adding the shielded wire opened me up to new and exciting errors in amp building.

Tell me if my thinking here makes sense, please:

I think a fine hair of the shielding wire that was too small for my eyes was making contact with pin 1 on the bass pot and pin 3 on the drive pot, so when the OD was activated and signal was going through the drive pot and some of that signal was getting fed back in where the bass would have fed if it were maxed, which is why it only occurred when the PAB and OD were both engaged, creating a feedback loop. As I understand it, the PAB essentially removes the tone pots from the circuit, effectively maxing them out. Is this correct?

[pompeiisneaks]

That's possible, also you could have accidentally melted the internal insulation where one strand of the ground wire is really close, but maybe not touching the signal wire and giving it way too much coupling allowing bleed. This is why that kind of wire helps AND can be problematic. I've had all kinds of random issues happen where I just removed the shielded wire and put in a new piece and it resolved it. There could be a dry solder joint too, on the bass pot, and the act of replacing it/changing it, fixes it as well.

You're finding how great chopsticks are at finding issues.... I poke and prod around with a wooden chopstick like mad until I find the problem area and most times it works.

You were right to be super careful with the plastic etc, that method is very dangerous as you can put B+ on your hand, or accidentally send B+ to places it shouldn't go and melt something bad etc, but sometimes, carefully handled shielding like that can also help isolate issues.

~Phil

[professormudd]

That's possible, also you could have accidentally melted the internal insulation where one strand of the ground wire is really close, but maybe not touching the signal wire and giving it way too much coupling allowing bleed. This is why that kind of wire helps AND can be problematic. I've had all kinds of random issues happen where I just removed the shielded wire and put in a new piece and it resolved it. There could be a dry solder joint too, on the bass pot, and the act of replacing it/changing it, fixes it as well.

You're finding how great chopsticks are at finding issues.... I poke and prod around with a wooden chopstick like mad until I find the problem area and most times it works.

You were right to be super careful with the plastic etc, that method is very dangerous as you can put B+ on your hand, or accidentally send B+ to places it shouldn't go and melt something bad etc, but sometimes, carefully handled shielding like that can also help isolate issues.

~Phil

Yeah, electricity scares me into paying attention. I still have some issues I think are all related. I don't think this is a single problem as much as a combination of adverse conditions all getting whittled away and occasionally introducing new issues. This is an adventure.

There was still a bit of what I can only describe as sizzle until I poked the wires into a position that it stopped. Might be worth re-soldering the joints on the bass pot.

[professormudd]

Right now, I have an amp on my bench held up by blocks that sounds great, and definitely has the amount of volume I would expect.

There were a number of things I did last night and this morning to get it working.

It seemed like it was definitely the OD channel that was the primary problem, though the clean still seemed low in volume. When I would engage the mid boost or PAB while clean, they behaved as expected in that the volume would get louder and the tone would change how you expect. But when OD was engaged, the volume would drop and the tone would thin out quite a bit, and when I engaged mid or PAB the volume seemed to dip even further. Also, the tone of the OD would sizzle when you held a long note.

I decided to go ahead and rip out the shielded wire from the OD pots and more carefully measure, cut, strip, and place. I felt like I was building a ship in a bottle or making tiny jewelry. After I get it all wired back up, I fire up the amp and the volume issues seem to be fixed! And now I have new issues! Lots of hums, buzzes, and hisses, oh my!

I poke around with a plastic poking device and move wires here and there. Whittling away little elements of the noise trying to adjust wire positions and stuff. Then we hit the ground bar's connection to the ground lug and it was like popping your back. Everything went silent and there was this wash of relief. I re-established good contact from that bar to ground, fired up the amp and it works! Properly (so far)!

I have been fiddling with this amp for 3 weeks, chasing issues and apparently introducing new ones as I go. I am too skeptical to take it off the blocks. Every time I thought I was done and buttoned everything up I had to take it out again.

But anyway, thanks to those who chimed in. Your help is appreciated beyond measure.

[pompeiisneaks]

Great! Glad to hear you sorted the gremlins!

We all love finished gut shots and sound clips if you can.

~Phil

[xtian]

Ha ha! It's never done! Now that you've finally got it running properly, the playing/listening/modding begins!

[professormudd]

I'll try to record some audio/video eventually, but in the meantime here is the janky cabinet I hastily built for it and a shot of re-done pot wiring.

[professormudd]

Ha ha! It's never done! Now that you've finally got it running properly, the playing/listening/modding begins!

Yeah, I am already thinking I should get the reverb on a footswitch. But maybe not today.

[pompeiisneaks]

Very cool, I love blue so I'm sold on that color already

~Phil

[professormudd]

It's a Bluesmaster, so I had to make it blue.