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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
12 responses Add your response
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.
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.
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.
tonyptony OP
617 posts
 
Riffer, where did you get one?
Post removed 
eldulcesol
197 posts
 
Tony, you might have a ground loop problem caused by the CATV line. Just get a couple matching transformers, solder one end of each transformer together keeping both lines seperate, tape seperatly, and insert between the cable line and tuner. You will need an additional one foot cable to do this. There is a slight signal lose which you might not notice, depending on how strong the signal is in the first place. If the signal lose is too much, try a Hugfen HF-NS 120 on the rca sound from the cable box to the tv. That worked the best for me. Got mine on Ebay for about $10 plus shipping. Good luck.......
riffer
362 posts
 
I got the Jensen at Markertek:

http://www.markertek.com/Product.asp?baseItem=JEN%2DVRD1FF&cat=VIDEOEQUIP&subcat=VIDPROCESS&prodClass=VIDEOHUM&mfg=Jensen+Transformers&search=0&off=

CATV is easy to check. Like you were going to do above, if the problem is CATV, when you unhook the CATV, the hum will disappear. It will be obvious.
tonyptony OP
617 posts
 
Update: I disconnected the CATV line and heard no real improvement. So I took the next (what should have been the first) step and disconnected / reconnected all my line level cables. I'm assuming it must have been this, because now the buzzing (it is still there) is so low that I have to stick my ear about 6 inches away from the speaker driver to hear it clearly. I may track down that last little bit at some point, but now at least I feel like I can play music without having some kind of anxiety attack.

Thanks to all for the feedback.
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