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What to do about my humming amp?

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5/30/2000 12:35 AM

What to do about my humming amp?

Hi all,

I own a peavey TKO115 bass amp (sorry, i'm building a tube replacement at the moment) actually i don't mind it, seems to sound pretty good to me.

anyway, the problem I have is that it hums. i've tried quite a lot, and i have found that the hum is in the preamp. (when i plugged a jack into the power amp input, all went dead quiet)

i've tried replacing each opamp, with no change in hum. does anyone have any other suggestions, should i maybe start replacing caps? (don't know why that'd create/remove hum)

anyway, i've run out of ideas, so any input is much appreciated.

thanks,
Rob

5/30/2000 11:57 AM

Rob
Does the hum also disapear when you plug your guitar into the preamp input jack? If so, then the jack contact on tip side may not be shorting to ground when the plug is removed,thus causing hum. Cleaning or replacing the jack would solve the problem.
Another cause, as you mentioned could be a bad or loose filter cap in the preamp power supply. Also look for any loose ground connections.

Good luck,
Bob

5/30/2000 10:34 PM
Rob P	Thanks Bob, I might give those a try. The amp hums when I'm plugged into the normal preamp input, but not when i plug into the power amp input.(doesn't matter if anything's attached to the other end of the lead). maybe i should just resolder the preamp connections (sounds like a bit of a bother though) how do you tell if a filter cap is good or bad? thanks, Rob

5/31/2000 6:10 AM
Chris Taylor	Since you are plugging into the power amp in, I think you are cutting off the preamp, thusly this means your prblem might lie in your preamp. Just a thought

5/31/2000 7:03 AM
Rob P	Chris, thats what i thought, but i'm not sure what to look at within the preamp. Rob

5/31/2000 11:59 AM

Rob,

I'm not sure what op-amps are in use, but you might try checking from pins 4 and 8 to ground, if they are 8-pin DIP op-amps. Use the DC and AC settings of your meter, and see what comes up - you would want to see + and - 12 to 16 volts at these pins, along with an extremely low AC reading. At least you can eliminate the op-amp power supply as a problem this way.

Ray Ivers
R.A.G.E. Electronics

6/1/2000 1:10 AM
Rob P	Ray, the opamps are 4558 types. i did actually check all the voltages at these, and they all checked out ok- i think they were +/-15V, i didn't check the ac, though. thanks for your input. i have to wait till the weekend to try out these suggestions, so forgive me if i haven't got anything new to say right now. Rob

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