Dual rectifier nasty buzz/hum

[JLHC495]

Sorry for the length...

Hi, I know there are a lot of threads about buzz/hum from these amps but I can't seem to find an answer to my situation. I have had my rackmount 2 channel dual rectifier for almost 15 years, so I know what is happening is not just normal hum. I'm getting a nasty buzz/hum from the amp, only when a guitar is plugged in. I have tried many guitars and cables, and have tried a ton of troubleshooting. I use the orange channel for high gain and the red channel for cleans. On the clean channel the buzz is negligible, but when I switch to high gain it is intolerable. I have a noise gate, but it has no effect. I also get alot of feedback.

Some backstory-- I first had this issue in 2011 and I actually took the amp in to an authorized shop. The tech said he did not hear any noise and that there was nothing wrong with the amp except a loose tube socket. He said he fixed that and cleaned the amp. I was upset at first, but when I got home and fired it up the noise was gone! It worked great for the next 2 years or so, then the noise randomly came back. This time I just tried troubleshooting all my cables, and the tubes(I have several sets of preamp and power amp tubes on hand). Eventually the noise went away again, but I had all the original tubes back in the amp and I have no idea how what I did could have fixed it. It worked great again up until now. All I did this time was swap out all of my rack gear into a bigger rack, and when I put it all together the noise is back. I didn't do anything to the amp itself and did not add anything to my signal chain. It almost seems like just the act of moving the amp around (I was careful of course) caused the problem to return. Like I jostled something loose or something. I'm just wondering if anyone has any idea of what could be causing this. Taking it in for service is a huge hassle, but may be my only option. I have already tried new tubes, plugging in to different outlets on different circuits, lifting the ground, different cables, removing all pedals, different guitars, different cabinets. Any help would be much appreciated and thank you for reading.

 

[afu]

If it's dirty or has a loose socket, you could pop it open while it's unplugged and check those. Wiggle the tubes and if any of them have more play than they should, tighten it up. Maybe tap the tubes lightly with a pencil and wiggle wires while it's powered on to see if anything crackles or hums from vibration. Did you try a different cable to the power amp?

If nothing seems to help, you should probably take it to a shop. Cleaning it and making sure things are secure won't hurt, though.

 

[Lotustar]

Having a similar issue with a 2x12 Maverick. Took it to a tech after replacing filter caps and tubes. He said electronics checked out fine and even replaced my power chord that had a short in it. Still no fix. Mine is a low hum even without a guitar plugged in. In any case, have you tried replacing filter caps? Pretty easy to do.

 

[JLHC495]

Thanks for the replies

When you say "cable to the power amp" are you referring to the speaker cable or the actual power chord? As far as cables I have tried everything. And none of them crackle or pop when shaken or pulled on. Tapping on the tubes doesn't produce any noises either.

As far as replacing filter caps I have zero experience servicing my own amps other than the tubes and fuses. I'd probably just leave that up to a tech.

I definitely don't feel anything loose in the tube sockets. If anything, they feel very tight. Removing and inserting both preamp and power amp tubes takes some effort. But then again, they didn't feel loose to me before the tech serviced it last time either...

I didn't think the amp would be very dirty again after only a few years, it is a rackmount version and I don't gig very often. It only gets played a few hours a week. There is a small layer of dust inside the amp, so I will open it up when I get some time and try blowing it out myself. If that doesn't help I'll just bring it in. I'll post what I find out if the issue ever gets resolved.

Any other suggestions or experiences with this type of issue are welcome

 

[3124+]

Maybe a ground loop through the rack rails? Try some shoulder washers to insulate.

 

[cyber104]

I had a very similar issue with a Peavey JSX Head. Although not a Mesa it did exhibit the same characteristics as yours does.

Swapping tubes often helped for a short period of time and just when I thought I'd fixed it the hum would come back.

It turned out to be the caps. I would stop wasting time trying to figure it out yourself and take it to a good tech. If the problem is consistent and you can demonstrate it to the tech it should be quite easy to fix.

 

[JLHC495]

Maybe a ground loop through the rack rails? Try some shoulder washers to insulate.

DUDE!! I think you nailed it!!

I took the amp out of the rack and tested it standalone and the noise was gone! I then re-installed it into the rack using a combination of rubber washers and electrical tape to isolate all parts of the amp's metal housing from the rack rails. I put my entire signal chain back together and voila! It worked! With my noise gate on, the high gain channel is actually quieter than the clean channel until I hit the strings!!

This would also explain why the tech didn't hear the noise last time. I brought it in separate from the rack. I hope other "Racktifier" users aren't having the same frustration... But man, I can't thank you enough!

My band doesn't rehearse again until Wednesday, I will report back to confirm the issue is resolved. I had a feeling it was something I was overlooking. Thank goodness I came here first!

Thank you again to everyone that responded!

 

[3124+]

When a problem comes along you must whip it.