Rattle & Rumble

[yardbird mac]

Nope... not an old 1950s rock & roll song, it's a problem that recently developed with my MESA/Boogie Express 5:50 (non plus) combo. I know it isn't the speaker. Over the past month I've tested several different speakers in this amp just for the sake of sampling different "flavors" of speaker tones/responsiveness. What I heard (a low frequency rumble/rattle that only occurs with certain notes in specific locations on the fretboard) was most pronounced with the MC90 Black Shadow installed. I believe that speaker has the heaviest low end response of the ones I tried, so it was pretty noticeable. After my speaker "tests" I re-installed the MC90 and I didn't notice anything unusual.

This morning I put the amp through its paces with a brand new WGS ET65. The unwanted "overtones" (or whatever they are) are back with a vengeance! In the brief time I had left after practicing this morning I tried to chase down what was making the "rumble" on certain notes (example; "B" played an octave above the "B" - 7th fret - low E string). The B played in that spot is not bass heavy, but the rumble is almost extreme in that position.

Since I'm by myself this morning I'm not able to play the "offending" notes on my guitar while attempting to see/feel what might be vibrating in the amp. The reverb tank in these amps are in a bag that's not securely fastened to the floor of the amp. I initially thought it might be that, but it wasn't. The protective tube cage is secure also so I'm at a loss as to the cause of this problem.

Does anyone have any ideas/suggestions?

Thanks!

 

[Don]

Hard to say. Could it even be a microphonic tube? They can sometimes "rumble".

 

[Newysurfer]

With all the mod'ing you do to your amps Mac it's probly a loose tube or screw somewhere.
You'll just have to go through the whole amp as a process of elimination.
The more you fiddle with things the more chance you have of this occurring eventually :mrgreen:

 

[yardbird mac]

With all the mod'ing you do to your amps Mac it's probly a loose tube or screw somewhere.
You'll just have to go through the whole amp as a process of elimination.
The more you fiddle with things the more chance you have of this occurring eventually :mrgreen:

Guilty as charged sir... Actually, since I obtained this combo in July of 2012, the only mod(s) I've done is trying different speakers. I eventually come back to the original C90 Black Shadow (up to this point). Even though the new WGS ET65 hasn't broken in yet, it shows a lot of promise for this amp. It's a lot more touch sensitive and smoother sounding. It has stronger mids, slightly rolled off highs, and a tighter low end than the C90. Once I get this "buzz" problem solved, I think the new speaker will work well in the combo, and except for eventually changing tubes (when necessary), I'll be done "tinkering". I'm getting burned out on chasing tone!

My 5:50 plus is a whole different ball game. I absolutely love the C90 in the 23" 1 X 12 open back cab I match with this head. This unit will remain stock. I have no desire to change anything, it's great "as is".

 

[melodiusthunk]

I think I have experienced the same rumble playing my 5:50 combo (MC90 speaker). At various times, I've had some success with all of the following:

1. Tightening the bolt that passes through the center of the amp chassis. This can help by effectively stiffening the chassis, thereby altering the resonant frequencies of the chassis.
2. Installing new power tubes (new pair). if one tube starts to wear out before the other, rumble can increase.
3. Change the amp position with respect to any nearby walls in the room. Especially if said walls are acoustically bright or reverberant.

Following your eval of the WGS65 with interest.