Plasma/amp hum

[goaliechris]

Hi all,

I know this is probably a ground loop issue but not sure how to solve this particular one. I have a Samsung 8000 series plasma and it is creating a hum through the speakers. If I turn off my amp (Rotel RMB 1095) the hum goes away. I have tried other combinations - cable box, cables, preamp, etc., and the issue is between the amp and the TV. I have both plugged into a Belkin PureAV power center but whether I have the TV or the amp plugged directly into the wall it still occurs. Also the hum does not change in volume if I turn the preamp volume up.

Any ideas on how I can defeat this hum as it's driving me nuts?

Thanks!

 

[Orbison]

Have you tried plugging both the TV and the amp into the same wall outlet at the same time?

Have you tried relocating come of the connecting cables that might be picking up the hum from adjacent power cords?

 

[Towen7]

It may be RF induction and not a ground loop. Is this a new problem?

My bedroom radio picks up interference from the plasma TV on the opposite side of the room.

 

[goaliechris]

It is a new problem since the large plasma was installed and it seems to have the same "sound" as the small hum that comes from the plasma itself. It sounds like that hum you used to hear from those long, large hanging flourescent light fixtures.

I have not tried separating out the connecting cables (balanced cables from the amp to pre) from other power cords but did try it with the TV power cord. Of course, unplugging the TV got rid of the hum which I failed to mention.

I will try plugging both into the same wall outlet and see if that helps at all.

 

[goaliechris]

Okay - this is different. I unplugged the balanced cables and the hum is still there. I tried normal audio cables and the sound is lessened to a great degree - a huge difference.

If I disconnect the speaker cables from the speaker, it goes away entirely.

So, turning off the TV gets rid of the noise. Turning off the amp gets rid of the noise if the TV is on. Disconnecting the audio cables between the amp and preamp does not if the TV and amp are on. The hum is far less with unbalanced cables. Disconnecting the speaker cables gets rid of the hum, of course. I'm a little confused.

 

[Rope]

Okay - this is different. I unplugged the balanced cables and the hum is still there. I tried normal audio cables and the sound is lessened to a great degree - a huge difference.

If I disconnect the speaker cables from the speaker, it goes away entirely.

So, turning off the TV gets rid of the noise. Turning off the amp gets rid of the noise if the TV is on. Disconnecting the audio cables between the amp and preamp does not if the TV and amp are on. The hum is far less with unbalanced cables. Disconnecting the speaker cables gets rid of the hum, of course. I'm a little confused.

The hum is always there when the plasma display is on regardless of source to the plasma? Is the plasma connected to the processor directly, or do you have a STB? Are you using HDMI?

Rope

 

[goaliechris]

The hum is always there when the plasma display is on regardless of source to the plasma? Is the plasma connected to the processor directly, or do you have a STB? Are you using HDMI?

Rope

Thanks for the reply. Yes, the hum is there regardless of the source. The plasma is connected to the Belkin power conditioner (though I have tried it directly into the wall). I am using HDMI from the TV to the preamp directly.

 

[Rope]

The hum is always there when the plasma display is on regardless of source to the plasma? Is the plasma connected to the processor directly, or do you have a STB? Are you using HDMI?

Rope

Thanks for the reply. Yes, the hum is there regardless of the source. The plasma is connected to the Belkin power conditioner (though I have tried it directly into the wall). I am using HDMI from the TV to the preamp directly.

Have you tried disconnecting the HDMI cable that passes the audio/video signal from the plasma to the processor?

This is kinda a monkey flew out of my butt theory, but if that connection is broken and the hum discontinues, it might be the HDMI cable causing your heart burn.

Rope

 

[goaliechris]

Good theory but unfortunately not that easy. I disconnected the HDMI cable from the TV to the preamp and it's still there. I need to take it all apart and start from scratch and start off simply and see where it is in the chain. If it's just interference from the TV power supply, how would I go about solving that? I guess trying to run the power cable to a separate circuit?

 

[Rope]

Good theory but unfortunately not that easy. I disconnected the HDMI cable from the TV to the preamp and it's still there. I need to take it all apart and start from scratch and start off simply and see where it is in the chain. If it's just interference from the TV power supply, how would I go about solving that? I guess trying to run the power cable to a separate circuit?

Then it definitely has to be the power souce, since that is the only other common connection from the plasma to the other related electronics. Try using a cheater plug, which is not a permanent fix, but it will isolate the hum.

Rope

 

[goaliechris]

Just tried the cheater plug - first on the TV, then on the amp. No effect - the hum is present at the same volume in each case.

The weird thing is if the speaker wire is connected to the speaker and I unplug the balanced cable, the hum is still there if the amp is on. If I unplug the speaker wire or turn off the amp, the hum is gone. If I turn off the TV with the amp left on, the hum goes away.

So, yeah....

 

[Rope]

Is it possible to connect the plasma's 115v cable to a different electrical outlet which doesn't share the same circuit on the breaker box?

Rope