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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
128x128balthus
santanaali
78 posts
 
I had the same problem with my Tube/SS Hybred and TT I just yesterday recieved a Granit Audio Ground Zero it solved the ground loop hum I had which is most likly what you have. Good luck
seandtaylor99
1,262 posts
 
Do you still have the hum when the preamp is disconnected entirely (with no cable attached to the amp inputs)? Are the pre and power-amps connected to the same outlet ? Just ruling out possible sources of ground loops.

also how old is the amp ? If it's old it could be failing power supply capacitors ? Just a wild guess.

The low frequency hum is almost certainly mains frequency (60Hz), so it's either coming through the amp's power supply, or via poor grounding somewhere.
elevick
2,638 posts
 
Ground Loop Hum most likely.
Unplug everything but the amp, power it up and listen for hum. If no hum, great! Continue by plugging in and turning on each component 1 at a time until the hum appears. Once you find the culpret, you can either deal with that units ground or the amp. This means that there is a ground loop issue which is easy to fix either with a "cheater" plug for 3 prongs to 2 prongs and then reverse the way it is plugged in.
If the amp hums when turned on, hooked up to the speakers buy no signal into it, then you have to deal with repairs most likely. Sometimes it is just vibrations that can be dampened by putting something under the feet of the amp. Weights on top may solve the issue but amps need to breath. Otherwise, in for repairs. It is very unlikely a tube problem.
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