my bass combo buzzes constantly. it must be a ground, but how can i fix it?

[jimgunnz]

The bass amp is from like 1994, Peavey TNT115 bass combo with 1x15" speaker that's 150 watts.
The amp buzzes as soon as it's turned on.
With or without a bass plugged in, buzz.
Different basses, buzz.
All volumes and tones down, buzz.
Tones and volumes up, buzz.
The buzz level never changes, even with volume increase.

There is a ground lift switch on the back, which I've tried in each of the 3 positions.
Sometimes the buzz gets a little better when switching, but it's negligible and still way noticeable.

I've tried it in several houses, several outlets and it still buzzes.
I did take it to a music store once to have it looked at, but when they plugged it in, it didn't buzz for them of course.
Is it possible that every single house I tried this amp in has bad wiring?
It must be the amp somehow, so how can I rectify that?

Let me know of any more info that might help troubleshoot!

[nashvillebill]

If it stopped buzzing when you took it in, but resumed buzzing after being taken back, I interpret that to mean that the physical movement of the amp affected the buzzing. (IMHO noise from electrical interference would be affected by volume so I'm ruling that out) This phenomenom (works at the repair shop but not at home) is not unheard of, something to do with Murphy's Law.

Enzo has patented a highly developed test method for determining such physical effects: take your hand and whap the amp HARD. Try several different spots, on top, on the sides...did the buzz increase or decrease?

My first guess would be that a filter cap has a broken solder joint. If I don't see anything obviously wrong with the solder joints with visual inspection (bad solder joints can be maddingly difficult to find sometimes) then I carefully plug the amp in with the chassis out, and physically wiggle/tap components with a non-conductive rod (a/k/a the "chopstick test") listening for any change in the buzz.

[jimgunnz]

Genius! You definitely led me down a good path, much appreciated. I first tried the whap test, lol. When I hit it towards the exit for the power cable, the buzz decreased. I hit it again and it increased. I figured some connection there. So, I unplugged and took out the chassis. Everything looks pretty mint, I must say! But I did notice one little guy hanging in the breeze that looked like he really wanted to be touching metal. So, I positioned him as such, plugged in the amp and voila!

So I think you were exactly right when you mentioned the physical moving of the amp. It definitely jarred that ground wire loose and once set right, all is perfecto! And to think, I was about to take it to the music store in the hopes it work there again and if not, to see if I could get anything measly for it!

Thanks again!

[nashvillebill]

Glad that worked, and that it was a simple fix.