Buzzy reverb troubleshooting in my amp

[Jaguar018]

I have a custom made amp that’s basically a Deluxe Reverb without the tremolo.

It’s in the form of an amp head, and when I engage the reverb it buzzes like crazy. The other amp I have, a Princeton Reverb is well within the ‘normal’ buzz range, so I don’t think it’s a house electrical issue.

The person who built the amp thinks it’s because the power transformer is too close to the reverb tank. I don’t have any real estate in the amp to play with.

What to do? Get a bigger clamp head cabinet?

[Jaguar018]

I took out the reverb tank and moved it around to be further from the power transformer. No noticeable difference in the reverb buzz.

[jdr1014]

Not sure but other simple things to check/rule out would be the cables and reverb driver tube. Good luck!

[burgrluv]

I had a similar issue with my '68 Custom Princeton Reverb, must have read about about a hundred different forum posts on how to fix it but nothing seemed to work, replacing the tube in v2 (reverb driver) did absolutely nothing despite that being the most recommended course of action.

What did work, however, was tightening the bolts on the input jacks and spraying contact cleaner on the rca jacks of the reverb cable. Took about 5 minutes and cut the reverb hum by about 75%. It's still a little noisy but well within healthy norms.

Might not be the exact fix you're after but given that contact cleaner is a very useful thing to own and only costs about $20, I'd definitely suggest you give it a shot.

[sookwinder]

First question:
have you removed the tank from the head and connected it outside of the head via long RCAcables … ie 3 or 4 feet away and checked whether the issue is still present? (maybe have the tank/bag sitting on a cushion or similar and not directly on the floor)

[Jaguar018]

First question:
have you removed the tank from the head and connected it outside of the head via long RCAcables … ie 3 or 4 feet away and checked whether the issue is still present? (maybe have the tank/bag sitting on a cushion or similar and not directly on the floor)

I took it out to get it further from the transformer, moved it around, and still got the same buzz. I didn't notice moving the tank affecting the particular buzz. I don't have any super long cables.

The amp builder also recommended I connect the amp to a different reverb tank, so I connected it to my Princeton's tank-- same buzz. So I'm pretty sure it's an internal problem.

[Again, I recognize there is generally going to be a low level 'buzz' with most Fender reverbs, and I have my reverb set on 10. With my Princeton amp, when I engage the reverb, there is that 'standard reverb background buzz sound' like at 10% or whatever that quickly gets lost when playing. With my other amp, it's like at 20% and it's just more in front. For the Covid Basement Rocking it's really annoying.]

[sookwinder]

Given my recent experience with magnetic resonance via the speaker in one of my amps, it was clearly apparent that the transformer (that was a transformer that was spec'd for a 50 watt amp) did not induce any feedback or hum in the reverb tank/circuit.

So if your experiment of moving the tank away from the head doesn't lower the noise then yes the only conclusion is that it is something in the actual amp circuitry that is causing the buzz.

This next suggestion you may or may not wish to do …. it involved removing valves.

Remove the 12AT7 valve (this is the first valve in the reverb circuit - does it still buzz?
Replace the 12AT7 valve back into its position and remove the 12AX7 valve from the reverb circuit - does it still buzz?

you may have to look at the valve chart or ask the builder which valves these are relative to everything else in the amp.

[Jaguar018]

I took the amp back to the builder, Pete Cage, who does a lot of amp repairs in the DC/Baltimore area-- great guy.

It turns out the issue was that the footswitch wasn't properly grounded. Fixed free of charge. Yay!

He also switched out the reverb's tube, a 12AX7 for a 12AU7-- just his personal preference-- and I have the 12AX7 to put back in if I like it more.

[Horsefeather]

That does illuminate what I think is a less-than-great design, running the signal out to a footswitch and back again. Simple and easy to build, though.