Strange distortion on certain notes

[maxkracht]

I added a larmar master volume to a deluxe reverb reissue and noticed a distortion that I haven't heard before. It's kind of an extra buzz after the note starts to decay. Only happens when the volume is past 5 and I hit certain notes kinda hard, more noticeable on higher settings. I did a handful of other mods, but nothing crazy. Just some better caps and resistors in a few spots and other misc de-cheapening. Not sure If this was a problem before any changes... https://youtube.com/shorts/5Ohpegt3ZQY?feature=share Any ideas? Please and thank you!

[xtian]

Lead dress might be an issue (parasitic oscillation). Might help to move wires around. Can you post photos?

[maxkracht]

I have done plenty of poking and wire moving and have since added a grid stopper to v2 for good measure. I haven't moved the power tube grid wires much, maybe I will try shielding the run from the MV to the grids. For my own ego, I did not rip the pad off the bright cap, someone was poking around a tiny bit in here before me.

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[maxkracht]

Should also note, the spike shows up on both channels, but is more prominent on the tremolo channel. It's also visible on the grid of the first stage, which would make me think parasite too, but I'm not sure what else to move, aside from shielding more stuff and cutting some traces. I added 50pf on the PI plates just in case, but no change. Tried a couple guitars, same problem. Think I have done all the obvious stuff, aside from the shielding and trace cutting that I don't particularly want to do...

[thetragichero]

have you tried the "enhance cap"? obviously tracking down any oscillations is step 1 but i've had situations where it just wouldn't go away and a 150-220pf cap across the first plate resistor in the phase inverter helped

[Stevem]

With any of the non ceramic caps that you have replaced and or add try removing them one at a time and then put them back in 180 degrees the other way.

[maxkracht]

I tried a 220p "enhance cap" on both PI plates, no change. Single note and buzz on a looper to troubleshoot is only slightly maddening...

With any of the non ceramic caps that you have replaced and or add try removing them one at a time and then put them back in 180 degrees the other way.

I'm not doubting the advice, but curious if you have fixed a similar issue with cap polarity. Aside from this problem, the amp is very quiet. I usually only whip out my little polarity finder device for high gain stuff. Also, I don't think fender would pay any attention to this in the first place, so Is it just dumb luck to get every cap in backward? Don't think I have changed any values or locations.

Might try to split preamp cathodes in case that's interacting in some weird way.

[Stevem]

In terms of tracking the source preamp tube wise you can try placing a 5 to 500pf cap from the plate to grid.

[maxkracht]

Thanks Stevem, I had previously tried caps from grid to ground on v1 and v2, and played with the PI, but didn't consider the reverb. It was still acting up with the reverb off so I had been mostly ignoring it... Fender had the reverb driver wired with the longest lead going from grid to grid and poking up into the heater. I assumed this was bad practice and usually jumper it closer to the tube socket with some PTFE sleeve. I kept the grid jumper and looped the cathode around the side and problem solved. I don't know how many times I have wired a parallel triode in this way without issue, even in somewhat high gain circuits... Does anyone have opinions on what the best practice is in this scenario?

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