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My "Hummer" is driving me nuts

I am new to tube equipment, so know very little about it. I purchased a British-made Grant power amplifier, 50 watts? per channel, four large tubes, four small ones. Sounds terrific, however, when the volume is turned all the way down, I can hear a low-frequency hum from both speakers. Not loud, but definitely discernable. Increasing volume does not affect the hum. I have ruled out the preamp as cause, having swapped in a second pre, also ruled out cable interference, as I've set up the system in two different rooms with different configurations and different cable and hum remains constant. My questions are, what might be the source of the hum? Will swapping out tubes eliminate it? Any suggestions on what steps to take next? Thanks! Ben
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elevick
2,636 posts
 
Forgot one other item: Do you have any other household items on that same circuit? A tv upstairs, a fishtank downstairs, a lamp in the living room...? This stuff can cause a hum. Try shutting off the breaker and see what else goes out.
foobagger
6 posts
 
Same problem after I added my external Adcom 5802. Low lever hum audible from speakers when no source sound playing. Disconnected other power leads. When I unplugged the TV power, the hum increased a few dB. Big clue. I then disconnected the CATV coax from my VCR and magically the hum got disappeared. Goodness. Looked on the web and found instructions for hooking 2 radio shack 75-300 ohm transformers in series as an AC noise filter. $7 in parts, and works like a champ. No deterioration of cable video quality discernable, and speakers now absolutely quiet. No need to spring for a $50+ isolator. Wishing all other 'hummers' similar success.
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hammy
176 posts
 
Ben, If you have nothing else plugged into the amp, and it still hums, It's not a ground loop problem. Ground loop hum occurs when one grounded component has a different electrical potential in the ground than another component. By using cheaters, you are eliminating the ground from all but one component, so there is no ground loop. I had to put cheaters on everything but my pre-amp, including one that de-grounds coax cable. You may have a different problem- the tubes picking up 60 cycle noise (a harmonic of 120 cycle alternating current). I can't say for sure, but I would exhaust the cheater idea before you re-tube.
kgveteran
377 posts
 
Your ,"Hummer" is driving you nuts.Oh,I thought you were dating my ex.
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