Amp noise question

[PeteeBee]

Riddle me this: my loud amp, a peavey musician iii, seems to make a noise like that of a blowing wind when it gets hot. Happens regardless of what is or isn't plugged into the input. One day I left the amp in my car on a hot day and it made the noise within the first hour of practice. Today it hadn't been in the heat and it took about 3 hours to make the noise.

Any guess what would cause this? Just dusty something or other?

[rfurtkamp]

Something's drifting out of spec with the heat.

[Hypnodrone]

Try changing the caps. Old and leaky caps often sound hissy. Cheap and easy Job.

[PeteeBee]

Thanks! I'll put new caps in. Hopefully that's it.

[crochambeau]

It's funny, I have a beat to shit mk 4 that exhibits almost the exact opposite behaviour. Fire it up cold and it'll spit all manner of noise at you, then it calms the fuck down once temperatures stabilize (5-10 minutes or so).

Since yours is taking a really long time to reach "failure" mode, I would suspect components that are not in the heavy lifting stages (power supply and output devices) since those reach temp fairly fast. It could be a bias resistor, or leaky cap, or poor solder joint in the preamp section as well. 3 hours is a long time to wait for the symptom to surface, and it would not surprise me if it's trapped ambient heat (inside the case) that triggers it - which would translate to the problem not surfacing while the amp is open for servicing.

If you self perform the work, I'd recommend going at it with a heat gun to aggravate localized sections so you don't waste hundreds of hours chasing your tail.

[tremolo3]

Same happens to my mark iv 400 after 1-2 hours of usage, but it's more like a buzz, a fucking loud buzz that I actually like, I wish it could be sent to the speakers.

[hbombgraphics]

It's funny, I have a beat to shit mk 4 that exhibits almost the exact opposite behaviour. Fire it up cold and it'll spit all manner of noise at you, then it calms the fuck down once temperatures stabilize (5-10 minutes or so).

Since yours is taking a really long time to reach "failure" mode, I would suspect components that are not in the heavy lifting stages (power supply and output devices) since those reach temp fairly fast. It could be a bias resistor, or leaky cap, or poor solder joint in the preamp section as well. 3 hours is a long time to wait for the symptom to surface, and it would not surprise me if it's trapped ambient heat (inside the case) that triggers it - which would translate to the problem not surfacing while the amp is open for servicing.

If you self perform the work, I'd recommend going at it with a heat gun to aggravate localized sections so you don't waste hundreds of hours chasing your tail.

this heat gun suggestion is one of the best things I have ever read, would never have thought of that,