Mesa Boogie Nomad 55 strange noise. Please help.

[kute27]

Hi. So my Mesa Nomad 55 2x12 is making strange noises, even when speakers are on mute. It seems like it's some kind of vibration, and it goes away completely if I apply some pressure to the top of the amp enclosure. Here is a video: https://youtu.be/ivLWd8UJVSs. Also tilting the amp backwards makes more noise. Does anyone have any ideas before I start unscrewing things? Any suggestions are appreciated.

[52 Bill]

Hi. So my Mesa Nomad 55 2x12 is making strange noises, even when speakers are on mute. It seems like it's some kind of vibration, and it goes away completely if I apply some pressure to the top of the amp enclosure. Here is a video: https://youtu.be/ivLWd8UJVSs. Also tilting the amp backwards makes more noise. Does anyone have any ideas before I start unscrewing things? Any suggestions are appreciated.

I couldn't watch the video, but it sounds as if there is something physically loose in the amp. If it buzzes or hums at about 60 hz, the power transformer may be loose or it may have a loose lamination.

Try tightening up the transformer mounting bolts, etc.

[Audiotexan]

I couldn't watch the video

Me either.

All Youtube gave was:

"Content Warning

If the owner of this video has granted you access, please sign in.

This video is private."

I can't tell from your description if the noise is electrical or mechanical.

More importantly: are you talking about hearing this noise through your speakers? Or just "in general" (eg: there's a rattling noise)?

[kute27]

Sorry about that, I fixed the video, shouldn't be private any more. Yeah, the noise is not coming through the speakers, so it's got to be mechanical vibrations I think.

[Pedro Vecino]

It could come from microphonic power tubes. An effect aggravated by the vibration of the mains transformer.
Try holding the tubes with your hands to see if noise stops

[TimmyP1955]

At first I thought it was a wacky telephone ringing in the background. I've never encountered anything like that.

[guitician]

Sounds like the reverb tank. Can you disconnect it? Or, a microphonic tube or electrolytic capacitor in the 1st stage would be my guess.

[Audiotexan]

Sorry about that, I fixed the video, shouldn't be private any more. Yeah, the noise is not coming through the speakers, so it's got to be mechanical vibrations I think.

Thanks for the video fix...sorry about the delay in getting back to you!

It sounds like a "two-parter" to me.
1. there's a definite mechanical rattle...the higher pitched "criiiiink criiiiink"
2. along with (what sounds to my ear like) a 60 cycle hum (low pitched, constant humming)

My guess says that, it's coming through the speakers, and then through the chassis itself. And that that (approx. 60hz) hum is generating the "mechanical resonance" in the chassis.

What my train of thought is at the moment is:

Usually there's a metal sheet (shielding) installed on the underside of the top piece of cabinet wood. If there's a low freq. (60hz) gently sweeping through that sheet of metal, perhaps where it got bent slightly at some point (due to removal of the head, or reinstallation of the head)..then that might be the higher-pitched "criiiiink criiiiink". (now it's metal on metal sound, so it'd have to be the bent portion coming into contact with the metal chassis of the head).

The only other thing I could think of is on some of the amps from that era, they used a "full wrap tube cage" on the output tubes...and perhaps that's what's rattling at that certain point (again, giving the "criiiiink criiiiink").

Given that most Mesa reverb tanks I recall seeing are in the bottom of the cab in a combo...and that both noises stop when you press on the top of the cab...it could also be that you're "killing" the offending "60hz" source, thus negating the mechanical resonance that's being created as an after-effect. (So that doesn't necessarily mean you have a tank issue. Only that it's extremely sensitive to that relative vibration. But, it's still something I would keep on the back burner to check though IF you get the steady low frequency nailed down first.)

I would check both the upper sheet of shielding, as well as the cage (if there is one) -as those are the only things I can think of offhand that would react to pressure being applied where you did in the video. (However, that's assuming you were applying a fairly heavy amount of force. It looked like you were though IMO.)

As to the origin of the "60hz" (again, my "description")...possible guesses include:

1. the Primary (mains) transformer
2. bad cap in the primary psu section
3. bad solder joints to ground somewhere in the audio chain (aka a ground that's now "floating" and injecting noise)

Again, just shots in the dark for ideas/things to check, as I agree. This is *definitely* one of the strangest sounds that I've heard.

It'd be a LOT of help if you have a dummy load (ideally 8ohm/50w) to plug in, which would help verify whether it's coming through the speakers or not though!