Amp Hum, most common cause(s) ???

[crunchman]

Noise could best be described as a low frequency hum with a fuzzy white noise.

I re-wired the heaters and inputs, the amp chassis was powder coated inside as well as out and I kinda think it may be a ground issue, I didn't remove a ton of the powder coating, could this be the cause ??? ...............Thanks !!

[Jazz P Bass]

Yeah I would think you need a good chassis connection.
Especially on the mains ground wire.
Actually it should be bonded.
Some builders use a screw, star washer, nut arraingement.
Is the hum obvious with nothing plugged in the input?

[crunchman]

The hum is the same whether plugged in or not, I'll have to get some paint remover, I'm gonna try oven cleaner first, I heard it works on powder coating.

Thanks for the input, I'll re-do all the grounds.

[crunchman]

Another thing, when i shut down the stanby the noise stops immediatly, the tone knob adds a hissing sound when increased, the volume just makes it louder.Also, a very loud pop when shutting down the standby.I will re-do the star grounds today............Thanks.

[crunchman]

Removed all the powdercoating and re-grounded without result, its exactly the same.No amout of chop-sticking affects the noise.

Back to the drawing board!

Add a very faint crackling type sound, noise disappears w/ either preamp tube pulled and disappears when power tubes pulled.

[Jazz P Bass]

What is important concerning "grounding", is that you complete the common connection as indicated on a schematic.
As long as all of the ground connections "connect", you are o/k.
Most builders prefer a star pattern.
Connecting to the chassis is convenient.
The green "earth" wire must be solidly attached to the chassis.
(can you say Code?)

[crunchman]

After checking every component in the preamp twice at least, and knowing the layout is aa proven design and all grounds are where they are supposed to be, I think I may have an open cap in the preamp.There is a 47pf mica there that I may have cooked, I have a .0047uf I can sub in to see, is this too large for the test or will it work to make a determination.If I recall using larger caps is ok but I don't know if there is a limit......Thanks