Super Reverb RI resonance/microphonics? Weird.

[stratomaster]

Hello,

I have a Super Reverb Reissue that has some mechanical vibration/microphonics problem going on (at least that's what I think it is). It only happens on certain notes (between the 7th and 10th frets on the wound strings, esp C and G) at higher volumes. What happens is when one of these notes is hit, a second tone is heard in conjunction with the first. It sounds like an electric razor or grinding metal, it’s just not as loud as the guitar note. But, it is very annoying and unmusical. I suspected the preamp tubes, so I replaced them all. It did not help. Then I took the chassis out of the amp and looked around. There didn’t seem to be any loose wires or bad solder connections, though I didn’t remove the board and look at the underside. I played through the amp with the chassis removed, and that seemed to have done the trick. This leads me to believe I have a microphonic component with something resonating nearby. It happens on multiple guitars, so it's not a fret buzz issue that is coming through the amp.

Has anyone dealt with anything like this? I'm open to any and all suggestions, because this is very baffling, and I need my amp for gigs.

[Chuck H]

This is a tough problem. It may be a microphonic componant or not. It could be the chassis or any mounting hardware is vibrating mechanically (this can be very decieving). If you can recreate the problem with the chassis out of the amp (maybe place it in front of the cabinet?) the best you can do is whack on all the signal chain caps with a wooden stick. If one is obviously microphonic, replace it. If that test doesn't reveal anything you can use a rubber object (not black) and press against the signal chain caps while recreating the problem. If damping any cap fixes the problem, replace that cap.

I have only ever seen this once. In a Marshall 900 series amp. And it was a small ceramic cap that was microphonic (or at least seemed to be). replacing the cap did fix the problem.

Chuck

[mikeboone]

Is your reverb tank disconnected when you have it out of the chassis or did you extend a cable to connect it? I once heard a really funky overtone coming out of a Twin that tuned out to be a corroded RCA connector on the reverb tank.

If so, disconnect the rev tank (with chassis in cab) and turn the reverb all the way to cut and see if that helps.

Do you have retainer clips for the power tubes or the spring style retainers. They vibrate in a combo and can cause microphonics.

[stratomaster]

Thanks for all the suggestions. I'll have to find a place to crank up enough to get an external chassis to start resonating and be able to work on the amp at the same time.

I always remove the reverb cables from the chassis when I open the amp. It was the first thing I suspected, as I have had reverb issues before. My power tubes have the retainer clips. No power tubes have ever caused this issue in the 4 years I've had this amp. It is a new issue.

What stumps me is that it only happens on certain notes. If it were general microphonics, wouldn't it affect all notes. And if it were a bad cap, wouldn't the full range of notes be affected?

[Enzo]

No, certain notes can resonate.

[stratomaster]

My problem has graduated! It now seems to be full-on microphonics. I can rap on the chassis and hear that same metallic clang coming through. Sounds almost like hi-hats closing together. I've never dealt with this before. What do you all recommend? Thanks.

[mikeboone]

It could possibly be a power tube?? Maybe, maybe not. Have you tried that? A light tap in the tubes would tell all.

Sounds like you need to get out the trusty chopstick as mentioned above and start poking (carefully) around in you circuit to see if you can find an issue. If you do, try re-flowing solder joints in the affected area. A fractured or cold solder joint is not always visible to the naked eyed.