What causes an amp to become noisy?

[jackevorkian]

I have an amp that, when its on, but not touching or playing the strings, has always been more or less silent. Lately, I hear background noise/speaker noise. The noise just sounds like...air...like when you turn a speaker up to 10 (or 11) you can hear the sound of air. But, I can now hear it at 4 or 5. When you start playing, you can't hear it, but as soon as there is silence or real quiet playing you can hear the noise. This just started happening. The only thing I did was mistakenly leave the amp on for about 10 hours one day. It seems crazy, but could that have done anything? Strange...

[Swarty]

I'd check preamp tubes first.

[John Phillips]

Tubes (including their contacts with the sockets), resistors (most usually carbon-comps, in certain locations, particularly plate resistors) or caps, in that order of probability.

Leaving the amp on for 10 hours could have done it, with the heat build-up over that time, but only if the component was getting very near to doing it anyway - so don't worry about having 'caused' it.

[jackevorkian]

Tubes (including their contacts with the sockets), resistors (most usually carbon-comps, in certain locations, particularly plate resistors) or caps, in that order of probability.

Leaving the amp on for 10 hours could have done it, with the heat build-up over that time, but only if the component was getting very near to doing it anyway - so don't worry about having 'caused' it.


Start with the preamp tubes or power? Would it likely be all the preamp tubes or just one of them?

[Zero Point]

Power tubes have a tendency to go bad first. Preamp tubes last a long time.

However, it is the opposite for microphonics and noise. Preamp tubes tend to get noisy and ... "tinkly" sooner. I've had amps in which the tubes have lasted many many years. As far as I know, David Gilmour has EL34's in his Hiwatts that have lasted over 20 years!

Just take care of your amp. Spend the time to keep your gear clean and in good working condition and this stuff will last a long time. Always have a warm up stage before you start using a tube amp. This helps with the longevity.

You can check the tubes for microphonics by GENTLY tapping them with a pick. If you can hear the tap through the speakers, and it is loud... that tube could be bad. Don't tap them hard tho. They are glass afterall.

If you play your amp loud and put some serious volume through the power section I'd check the tubes every 6 months or so. Also, amps tend to collect a lot of dust. So cleaning the pots with contact cleaner while the amp is off... could help.

Good luck man!

-Z

[AL30]

My old college roommate could make an amp noisy in the span of about 30 seconds.

You don't need to swap out all the pre-amp tubes (maybe). Take a known good pre-amp tube and swap it for the other pre-'s. Keep doing this until the noise goes away. This may take care of the problem if it's a single tube. And, as Zero Point said - you can gently tap on the tubes.

AL