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One hum problem solved, another remains

I had recently relocated my equipment to another room, where I can now integrate my 2 channel gear into a multichannel rig. In my old room I never noticed any sort of ground hum problem, but I was faced with two when I turned on my stuff in this new setup.

The first one was easy to solve. It was apparent only on my phono input and increased in volume with an increase in preamp volume. Pretty loud, too. It turned out that I accidentally connected the ground lead from my phono cable to my phono preamp. In my particular setup this produces a real buzz. So that one was now taken care of.

The second is noticable on all inputs, does not increase with volume, and really can just barely be heard with my ear about 1 foot away from either speaker. But I don't remember it in the old room. In this new setup the amp is plugged into a different outlet from the rest of my gear. I tried flipping the polarity of the plug on the amp with no success. Every other piece of equipment is on a three prong plug and is plugged into a Wiremold L10320. I don't know if the two different outlets are on the same breaker.

Any help would be appreciated.
tonyptony
boa2's avatar
boa2
1,551 posts
 
If the hum is loud, it may be a grounding issue. I've solved a few with 3-into-2 cheater plugs, usually on an amplifier. If it is low level (sounds more like it from your description), I would gently check the IC connections, as well as power cord and cable routing. Often, the difference between hum and no hum is moving a cable a couple of inches.

Also, if you have tube gear, you can also get a hum coming from tubes that are either well out of bias, a bad tube, or a tube that is not making a good connection in the socket. Less likely--but I've had it happen--is a bad tube socket.

Hope that helps.
johnjbarlow's avatar
johnjbarlow
175 posts
 
If you have a tube amplifier, it is normal to hear a quiet hum when placing your ears near the speaker. If you can't hear it from your listening position, it shouldn't be a problem.
tonyptony OP
615 posts
 
Boa, John, I have a Van Alstine FetValve, which is a tube hybrid. But the driving stage is FET (not tube), and I never heard this in the other room. In this room there is a lot more stuff, including my HT setup (such as it is). I've heard that analog CATV lines are often the cause of this kind of thing. When I get home I intend to disconnect the CATV feed to see if it goes away.

There are a few more cables now, so I think it's also a good idea to be prepared to move these around.

If the hum does not really increase in volume is that a good bet that it is either being picked up through the lines to the amp (power, IC) or within the amp itself? That is, as opposed to anything before the preamp.
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