Vibration problems in a Peavey Combo 300 Bass amp

[bewater]

I'm the original owner of one of these Peavey Combo 300. Since the first day i noticed a great (and annoying) vibration (nasty noticeable sound) from the Combo structure: As if the amp had a friction with the cab structure or if the cab structure were not well fixed. A technician put a piece of foam between the amp and the wood and the vibration was reduced in a 95%. All these was 20 years ago!!!

Nowadays, after 13 years without run the Combo 300 I decided to restart playing with it. The vibration now is incredible and annoying, a total **** impossible to play. Specially some notes (low B, C in a 4 string Bass) generates a full vibration.

Have someone noticed this kind of problem with the Combo 300?
Solutions?

How can I fix this cab/combo? Is there any easy solution?

Thanks and happy 2009!
Josep

[Enzo]

ISolate the problem. You can make a stethoscope with a rolled up magazine held to your ear. That helps localize the noise source.

Nothing special about the COmbo300, any amp can buzz.

Is it the metal chassis? The grille? Pop the grille off and run without. Does that stop the buzz? SOmetimes the top edge of the grille buzzes against the bottom of the metal chassis. That is where to stripe some weather stripping if so.

Make sure all the mounting hardware is tight. A loose screw will buzz all the time.

Is the speaker loose? Check the screws.

Pull the chassis. Are the mounting screws for the power transformer tight? ANything else loose?

With your hand, press hard against various places on the cabinet and chassis. The middle of each side panel or hte rear panel. Press against the edge of the chassis. Press against the rear of the chassis. If pressing against anything stops the buzz, we are close to what is loose.

Very rare but popssible is delamionated plywood. If the glue fails between layers in teh plywood, a buzz can result. A screw through it usually cures that. If this is particle board, then never mind.

[bewater]

Ok Enzo, thanks, I'll try to check all that.

First of all I keep off the grille. It was part of the vibration (one of them). The most annoying continue.

I'll try the next days to check the origin of this great vibration, following your advises to find it.

Thank you very much!

[drewl]

Hmmm.....I got one of these with a vibration that's being amplified, creating a really nasty distorted crackling vibration type sound.

Tried another speaker cab, and it still does it.
" A " 440hz is the frequency that really makes it go nuts.

I had previously repaired this amp, and I know I had reflowed alot of the pc board connections.
I haven't opened it up, but I'm going to try and isolate where the noise might be coming from, pre amp or power.

Any ideas what might cause it besides a bad connection somewhere's?

I'll post what I find.

[Gtr_tech]

Hmmm.....I got one of these with a vibration that's being amplified, creating a really nasty distorted crackling vibration type sound.

Tried another speaker cab, and it still does it.
" A " 440hz is the frequency that really makes it go nuts.

I had previously repaired this amp, and I know I had reflowed alot of the pc board connections.
I haven't opened it up, but I'm going to try and isolate where the noise might be coming from, pre amp or power.

Any ideas what might cause it besides a bad connection somewhere's?

I'll post what I find.

Check the coil on the spkr output. It'll be large-ish and constructed on brown paper. The leads tend to crack at the standoffs and make intermittant connection.

[Gtr_tech]

Ok Enzo, thanks, I'll try to check all that.

First of all I keep off the grille. It was part of the vibration (one of them). The most annoying continue.

I'll try the next days to check the origin of this great vibration, following your advises to find it.

Thank you very much!

Its possible you have either a loose magnet on the speaker (it bolts on) or the black foam plug in the rear vent has decomposed and bits have been sucked into the magnet gap.

[drewl]

Would that cause the extension cabinet to produce the noise also?

i was running both the internal and an external speaker and got the noise.

With the head on the bench it's okay, so it's definitely a vibration problem.

I have to run more tests.

[Enzo]

If you left the internal speaker connected, yes, it can interact with an extension.

[J M Fahey]

If chassis on bench cures it, then itīs somethimng loose there.
Beat it everywhere with a chopstick until you find some reaction, then tighten, resolder, reseat, hot glue the offending part, whatever's necessary.
Good luck.
PD: and *still* it might be the output inductor gtrtech suggested !!!

[drewl]

Well I think I finally cured the vibration problem, I think I'm deaf now from beating on notes with it cranked up!

I reflowed even more pc board connections, anything that even remotely looked funny, and went nuts with the hot glue gun.
I glued all the electrolytics, any parts that were touching got some glue like the output coil was sitting on it's resistor.

I used lock washers for the pc board mounts, but what I think may have had the biggest impact is I put glue on those little pc board mounting brackets that are riveted to the chassis.

So, file this one away in case you run across the same problem.