Center channel hum

[gtDark]

Hey guys, I haven't been on the forum in a long while, and I remember how much I hated to read threads on this topic, but I gotta ask your opinions, since now it's different since it's me with the problem .

Here are the main characteristics of the situation:

-RC-7 on top of 27" CRT TV (with a relatively noisy power supply)

-Upstream of the RC-7 is a Parasound amp (3-prong/ground power cord adapted to 2-prong plug directly into wall outlet, "cheater" plug) and a HK receiver acting as pre/pro (2-prong plug into surge protector)

-Sounds like an electrical hum, comes out of both woofers and the tweeter, haven't put an SPL meter on it, but it's quite noticable from the listening position 9 feet away

-Hum is source independent (i.e. still hums whether dvd player on/playing or off) and gain independent (i.e. doesn't change when you crank the volume on the pre/pro)

-Other front speakers are RF-3's, no hum

What I've done to try and locate the problem and results:

-Changed out the speaker wire (no excess length, not coiled) and RCA interconnect -> No effect

-Run the speaker wire away from the TV and placed the speaker about 5 feet away from the TV -> Little to no effect

-Swapped the interconnect running from the center channel pre-amp output of the receiver to a different input channel on the amp -> hum does not shift to the new channel, stays in the center channel

-Swapped the center channel speaker wire from the center wire taps on the amp to a different output channel output taps (with center interconnect correctly going to center input on amp) -> again, hum does not shift to the new channel

Well, that's about all I can think of off hand. I sincerely appreciate any advice or recommendations or thoughts on this matter!

[DRBILL]

Hum in the audio community is something like Original Sin. No matter what you do, a little taint of it still remains to remind you of your vulnerability. Remeber that you heard it here first.

DRBILL

[travisc]

does it stop when you turn off the tv?

[scriven]

If you have cable TV you could have a ground loop from the separate ground path via the cable connection.

[WMcD]

Tell us more.

1) Is this a new set up. It seems like it. If not, what changed just before the hum appeared.

2) It seems you're saying the TV is not causing the hum. When you move it away, you say little or no effect. Does that mean little or no change, or little or no problem? i think you mean the first and the TV is not the source. Agin the earlier posted question of whether it goes away when the tube is off.

3) It seems you've eliminated a ground loop if the other channels do not have hum. A ground loop should affect all.

4) Are you not describing that your center channel amp has a hum in the output. If you hook another speaker to it, does that speaker hum? If so, it is definitely the amp.

5) If there is peramp, maybe the problem arises from the connection between the preamp and the main amp. Check the RCA connection between the two.

5.1) A friend bought Monster RCA interconnects. The darn things have very stiff collar-ground connections which make it difficult to mate with the amp input. The thing is so stiff that it might damage the amp connection if you force it on or off. It is also a bit difficult to see whether the collar is engaged; the mechanical bind makes you think it is engaged, but it is not.

I used some long nose pliers to adjust the collar. Then it engaged properly for a good connection.

= = =

Please let us all know how this works out.

Gil

[Guest BobG]

Did you mention whether you physically moved the center speaker away from the TV? Several reports of the magnetic field created by tv causing noise in the center speaker.