Loud buzz - none of the obvious culprets...

[CA_Dan]

I've got an Ampeg B4R in for a constant buzzing sound. The amp is a solid state 1,000 watt bass amp. The buzz occurs as soon as the power is switched on, and it doesn't matter if anything is plugged in to the input jack or not. I tried plugging straight in to the effects loop return and power amp in and the buzz is still there. It sounds like a signal short to ground or something like that, similar to grid resistors going bad on a tube amp. I cleaned all the jacks and pots with DeOxit and the buzzing went away, but came back when the customer took the amp home and tried it out. Now I can't get it to go away. The amp is about 10 years old and is gigged regularly. Any ideas?

[SatelliteAmps]

Cold solder joint on a ground connection, jack or one of the pots, maybe.

[Jerry Glass]

I had an Eden Nemesis bass amp in that had a loud hum. One of the main filter caps had failed (open). The amp still technically worked aside from the loud hum (unfiltered DC on one rail). Not sure this is your issue but I would at least check the cap's connection to the board.

[CA_Dan]

The power stiffening caps are 8200uF and my DMM only goes up to 999uF in the display. The caps look good and are higher quality, and the buzz doesn't increase or decrease with the volume control like bad power caps usually do. I'm thinking it could be either of these two:

1) the bridge rectifier has failed pumping AC or one half of the AC power to the rails.

2) a coupling cap failed allowing DC current to pass between stages

Do these seem like reasonable area to check into? I'm also going to check all the solder joints.