Help needed with subwoofer hum

[dkwong]

Here's my situation. I have some in-wall cabling in my house for 4 speakers and a sub. I'm only getting the humming with the sub, so I'll just concentrate with that wiring. The in-wall cabling for the sub is about 20-30 feet long and terminates with a wall plate with RCA jacks on one end and dangles freely on the other end. I attached an RCA plug to the free end so that I can connect it to my receiver. Now, with the STF-2 connected to the wall plate and no receiver connected to the other end, the sub emits a very noticeable hum. When I disconnect the STF-2 from the wall plate, the hum goes away. Also, when I connect the other end to my receiver, the hum also goes away. During normal usage, I don't hear any hums and the sub turns itself on and off correctly -- the hum only occurs when the other end of the sub cable is not connected to the receiver.

I've tried disconnecting my cable TV cable and the hum remains. The STF-2 has a 2 prong electrical plug, so a cheater plug wouldn't help there. What else could be causing this hum? Should I even worry about it since it doesn't occur with everything connected together? Thanks.

[Dudley]

If a subwoofer hums in the forest, does it make a sound?

I would not worry about it, since it does not occur when it is hooked up correctly.

I would guess that the cable is acting like some kind of antenna, and causing the hum - plugging it in grounds it.

[dkwong]

That makes sense. Thanks for the help!

[octalon7]

First time post, I'll post this here, hopefully it won't get lost amongst the old posts, but I've found some unwanted noise in my system as well. I note dkwong this won't solve your ground problem, but I'll post for others who may be trying to solve ground problems as well.

Ground loops are the biggest pain to find sometimes. What I ended up discovering is that the noise was coming from my cable. If you have your HT or stereo setup somehow connected to your tv or your cable box, or any combination, you could be seeing a grounding problem that is coming from the cable company. There is a fix for this. It's not intuitive for us nonelectrical people but I'll try to explain what a phile friend of mine told me to try.

Buy these two parts from Radio Shack, or wherever you can get them, or dig through your old tv parts and find them:

Transformer (300 ohm to 75 ohm transformer):
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=15-1253

Matching Transformer (75 ohm to 300 ohm transformer):
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=15-1140

Connect the two together, essentially going from the 75 ohm cable to the 300 ohm flat connections back to the 75 ohm and in to your tv or wherever the connection coming from your cable outlet connects to first. IE if you have cable from wall to cable box to tv, put the transformer piece in between the wall and your cable box.

There is someone out there that makes this part as one solid piece, but if I recall correctly its way overpriced. Just buy the 2 parts for $5 and give it a try.

This may solve your grounding problems, or it may not, but it's a cheap suggestion to try. Good luck and sorry if this suggestion is somewhere else on the msg board.

[Sasha_G]

Cable TV installers often ground the signal cable wherever they feel like it, instead of on the same ground as the rest of the house. This causes a conflict in the electronic properties of sensitive components.

The cheapest solution would be to get several Radio Shack ground isolators for fifty cents each and run them so none of your home theater uses the ground.

Unfortunately, most people do not feel comfortable with this. For those, Ground Loop isolators will work. Here is one:

http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=18383449&St=1535&St2=64201554&St3=-55957076&DS_ID=3&Product_ID=16262&DID=7

I tried this one out on my Direct TV system. No problems for a few days, then DirectTV started having trouble downloading program guide material from the dish. I removed it and the program guide downloaded. It might be a coincidence, so I'll try again to recreate the issue.

[Retread]

Originally posted by Sasha_G
Cable TV installers often ground the signal cable wherever they feel like it, instead of on the same ground as the rest of the house. This causes a conflict in the electronic properties of sensitive components.

The cheapest solution would be to get several Radio Shack ground isolators for fifty cents each and run them so none of your home theater uses the ground.

Unfortunately, most people do not feel comfortable with this. For those, Ground Loop isolators will work. Here is one:

http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=18383449&St=1535&St2=64201554&St3=-55957076&DS_ID=3&Product_ID=16262&DID=7

I tried this one out on my Direct TV system. No problems for a few days, then DirectTV started having trouble downloading program guide material from the dish. I removed it and the program guide downloaded. It might be a coincidence, so I'll try again to recreate the issue.

I bought a high-end ($50) isolation transformer for my cable. Works fine. However, it only eliminated one source of hum. The basic problem is the unbalanced signal leads. If one has a complex electronics setup, the potential for loops multiplies. For instance, I have a DVD player, a Receiver, a TV, a front projector, and a computer all connected, mostly with unbalanced leads, since that's the way sub-professional electronics are delivered. I've pretty well got things worked out so hum and other noises are under control. However, I wanted to put a Rane parametric equalizer in the path to the sub. The Rane uses balanced inputs and outputs. I've yet to be able to make the connection without big-time hum. I've bought some high-end balanced audio isolation transformers, to try to fix it, but haven't had time yet to do the connections.

[tobz]

Cable TV installers often ground the signal cable wherever they feel like it, instead of on the same ground as the rest of the house. This causes a conflict in the electronic properties of sensitive components.

Thank you!!!! DTV came out last week with a new dish and HD DVR - BAM! subwoofer hum. What the hell? Never had a hum. Group loop hum..what's a ground loop hum? Crap, web research, unplugging this component that component... then read your post! A DTV quality control guy came by after the install and decided to ground the cables to an existing water line that goes up the side of the house. Unscrewed the ground line.. bingo! No more hum.

Now i have to figure out the correct way to ground the satellite lines, but I've survived 6 years with ungrounded lines, I can survive a few more until I figure out the right solution.

Thanks again! Hum free viewing!!!