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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
tonyptony OP
617 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.
boa2's avatar
boa2
1,551 posts
 
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.
Sounds like a very good idea.

If it was coming from the amp, it should increase in volume with a turn of the volume knob. At least that's what I've experienced. However, because you say it is not, I would suspect cable line (#1), and then check other cables for routing.
amandarae
512 posts
 
I would recommend using a shielded cable from main preamp to the amp. Same is true for the phono input to preamp or through phono preamp to main preamp.
tonyptony OP
617 posts
 
Amandarae, I'm using PAD Venustas from the pre to the amp. These are very well shielded. But, I am using unshielded Kimber KCAG from the phono pre to the pre. I can replace these as a test with shielded ICs. But if it was coming from this area I still think the hum would be increasing with volume.
riffer
362 posts
 
I have a problem with the CATV. Solved with the Jensen VRD-1FF.
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