My plasma TV causes my subs to hum - AVS Forum
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post #1 of 27 Old 03-09-2014, 04:37 PM - Thread Starter
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This doesn't appear to be a ground loop issue but please correct me if i'm wrong.

When I power on my 65" Panasonic VIERA TC-P65VT50 plasma TV, it causes both my subs to have an very noticeable oscillating hum. It seems worse with a bright / white screen. With a black screen, the hum is not noticeable. No other part of system needs to be powered on or connected. The amps, pre-pro, BD player are all unplugged from the wall. I don't have a cable box. The subs do not have their XLR cables connected to the pre-pro. All i am talking about here are the power cords for TV and subs. All I have to do is power on the TV and pick a white screen and the sub hum starts. One complete cycle of the audible hum takes around 8 seconds. There are about 2 seconds out of the 8 seconds where the subs are silent. Eight seconds is a bit weird for cycle time but i'm not a plasma expert.

The TV has a three prong power cord and so do the subs. If I plug both the TV and the subs into a power strip so that they all use same wall outlet, hum is still there. If I plug TV into an outlet across the room, far away from wall/outlet with sub but still same circuit, hum is still there. It seems that if I plug TV and subs into same outlet or different outlets in the room, the hum is always there. All I need to do to get rid of hum is turn TV off or make the screen black.

If I put 65" plasma TV on a different circuit in the house than the subs in HT room (i had to go out of HT room to an adjacent room with a really long extension cord), the very loud oscillating subwoofer hum that is audible with a white screen completely disappears and is replaced with a constant hum that is only barely noticeable with my ear right up against the subwoofer. The subwoofers appear completely silent when i'm at the MLP. It is a huge improvement.

So apparently, the plasma on white screen draws enough power for the subs to generate a hum.

The HT room is on a normal 20 amp circuit.
The breaker has never tripped while playing loud bass heavy movies but i am curious how close to 20 amps i am getting.

Possibly dumb question:

Can the 65" plasma TV on a white screen cause a big enough voltage drop in the room circuit that the subs "see" it and produce a hum? Why is the hum cycle time 8 seconds?

thanks in advance

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post #2 of 27 Old 03-09-2014, 06:27 PM
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I suspect that the signal cables to the subs are picking up some EMI from the TV. Take a look at them, you may want to replace with better shielded cables. Quad shield RG6 with solid copper core would be my fist pick.
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post #3 of 27 Old 03-09-2014, 10:15 PM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post

I suspect that the signal cables to the subs are picking up some EMI from the TV. Take a look at them, you may want to replace with better shielded cables. Quad shield RG6 with solid copper core would be my fist pick.

I don't think so:
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No other part of system needs to be powered on or connected. The amps, pre-pro, BD player are all unplugged from the wall. I don't have a cable box. The subs do not have their XLR cables connected to the pre-pro. All i am talking about here are the power cords for TV and subs.

B&W 802 Diamond mains, B&W HTM2 Diamond center, B&W 804 Diamond surrounds, Parasound HALO A 51, Krell KAV-300i , Integra DHC-80.3 pre-pro, two JL Audio Fathom f113 subs, Panasonic TC-P65VT50 65" plasma
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post #4 of 27 Old 03-09-2014, 10:21 PM
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if the cables are connected to the subs they can act like antennas, even if they aren't connected to the pre-pro. If you haven't tried yet disconnect the cables at the subs and see if you still have the issue.
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post #5 of 27 Old 03-09-2014, 11:03 PM - Thread Starter
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They are not connected.

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post #6 of 27 Old 03-10-2014, 06:34 AM
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have you tried lifting the grounds on the sub amps?
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post #7 of 27 Old 03-10-2014, 10:32 AM - Thread Starter
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That was next on my list. That is the 3 prong to 2 prong plug adapter right? Available at Home Depot.

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post #8 of 27 Old 03-10-2014, 10:50 AM
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right, basically disconnecting the ground wire.
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post #9 of 27 Old 03-10-2014, 11:01 AM - Thread Starter
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I am trying to find on HD website now

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post #10 of 27 Old 03-10-2014, 03:05 PM
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just a cover my @zz statement. disconnecting the ground can be dangerous and may damage equipment so proceed with caution.
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post #11 of 27 Old 03-10-2014, 05:34 PM - Thread Starter
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it didn't work

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post #12 of 27 Old 03-10-2014, 06:04 PM - Thread Starter
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Is it possible the big amps in the subs can "see" RFI from the plasma when the plasma is working hard at making a white screen?
Maybe the plasma is emitting so much energy through the air that the sub amps are picking it up?
Maybe when the TV is on different circuit, it kind of changes the cycle or something so that the sub amps don't see the RFI?

B&W 802 Diamond mains, B&W HTM2 Diamond center, B&W 804 Diamond surrounds, Parasound HALO A 51, Krell KAV-300i , Integra DHC-80.3 pre-pro, two JL Audio Fathom f113 subs, Panasonic TC-P65VT50 65" plasma
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post #13 of 27 Old 03-10-2014, 07:11 PM
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You could leave it plugged into the outlet causing the hum and move the sub as far away from the TV as possible, that would answer that question
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post #14 of 27 Old 07-14-2014, 12:37 PM
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Quote:
Originally Posted by bao01 View Post
Is it possible the big amps in the subs can "see" RFI from the plasma when the plasma is working hard at making a white screen?
Maybe the plasma is emitting so much energy through the air that the sub amps are picking it up?
Maybe when the TV is on different circuit, it kind of changes the cycle or something so that the sub amps don't see the RFI?
Were you able to figure out what the issue was?

I have the same exact problem with my ZT60 and JL F112. It has followed me to my new house as well.
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post #15 of 27 Old 07-14-2014, 08:57 PM - Thread Starter
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Unfortunately no. I am living with the hum when screen is white/bright. There appears to be no good answer. I tried a lot of things. sorry

B&W 802 Diamond mains, B&W HTM2 Diamond center, B&W 804 Diamond surrounds, Parasound HALO A 51, Krell KAV-300i , Integra DHC-80.3 pre-pro, two JL Audio Fathom f113 subs, Panasonic TC-P65VT50 65" plasma
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post #16 of 27 Old 07-15-2014, 10:03 AM
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Originally Posted by bao01 View Post
Unfortunately no. I am living with the hum when screen is white/bright. There appears to be no good answer. I tried a lot of things. sorry
How close are the subs located relative to the plasma TV? If they are close, does moving the subs away from the TV affect the level of the hum?
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post #17 of 27 Old 07-15-2014, 10:31 AM - Thread Starter
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6' and 22'
no

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post #18 of 27 Old 07-15-2014, 10:36 AM - Thread Starter
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i am hoping that when i change to a nice projector and screen instead of plasma, the problem will go away

B&W 802 Diamond mains, B&W HTM2 Diamond center, B&W 804 Diamond surrounds, Parasound HALO A 51, Krell KAV-300i , Integra DHC-80.3 pre-pro, two JL Audio Fathom f113 subs, Panasonic TC-P65VT50 65" plasma
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post #19 of 27 Old 08-30-2014, 01:02 PM
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I have this exact same problem. Panasonic TC-P65ZT60, two Martin Logan Descent-i subs.

Happens when screen is bright (mostly whites), goes away when screen is darker.

Subs are about 5' from panel, and can't be relocated due to room layout.

Full-range left and right RCA from power amp goes to subs' full-range inputs, and XLR .1 channel (Y'd at preamp) goes to subs' .1 input (configuration reviewed and approved by Martin Logan).

Kuro didn't do this--we only heard only very quiet sub hum (and if you look at our system per my signature, you'll see the metal conduit and grounding and Furman we used to minimize the hum).

Having already had to add vents to quiet the fan noise on the Panasonic (Panasonic ZT60 and VT60 Fan/Fridge Noise Production Numbers), this latest problem is particularly disheartening.

My system? Google for: Martin Logan 420 CLX Descent Stage Summit
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post #20 of 27 Old 11-17-2014, 11:59 PM
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Any resolutions to this?

I ran across this at Music Direct and might give it a shot. http://www.musicdirect.com/p-7021-st...ers-cloth.aspx
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post #21 of 27 Old 11-18-2014, 01:33 AM
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Any resolutions to this?

I ran across this at Music Direct and might give it a shot. http://www.musicdirect.com/p-7021-st...ers-cloth.aspx
For now I have the Panasonic in its original box and the Samsung on the wall.

My system? Google for: Martin Logan 420 CLX Descent Stage Summit
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post #22 of 27 Old 11-18-2014, 07:56 PM
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If I am understanding correctly, the subs are picking up this hum without any inputs connected to them. In other words, they are connected to power only? Is that correct? It sounds like your plasma TV is generating interference that is being fed through the AC power cord into the power system and then through the power cord into the subwoofer.


The fact that plugging the plasma into a different circuit eliminates the noise backs this up.


It may be that your plasma is producing more noise than it should, and/or it may be that your subwoofer is more susceptible to noise than it should be.


Does the plasma being on and displaying all white generate noise in any other components?


You say that you get a very slight hum in the subwoofer. Does it change when plugging it into a different power circuit and/or when you remove the input cables? It may be that the subwoofer always produces a little noise, or if it happens only when the input cables are connected, it could be a ground loop. But this does not sound like your main problem.


The fact that sound hits a null every 8 seconds or so leads me to believe that the problem is tied to the plasma's sync rate, which will be different than the 60 Hz power frequency. Video and computer resolutions are typically based on a "60 Hz" timing that is actually "59.94 Hz". As this goes in and out of phase with the power frequency it will get louder and quieter.


Try feeding the plasma a signal with a different refresh rate. Use a computer as a source (ideally a laptop running on a battery to eliminate any concerns with ground loops). Try changing to different resolutions with different scan rates to see if the interference changes. If it does, that is a pretty good indicator that the circuitry in the plasma is generating the interference. The fact that it happens most when the plasma is displaying a bright white screen certainly points in this direction. That's when all the pixels are lit up, the plasma is working the hardest and there would be the most potential for noise generation.


It sounds like you have already done this, but if not, try unplugging all input cables from the plasma end of the cable (as opposed to the signal end). If this helps, they were likely acting as antennas and radiating the interference. Try connecting each cable one at a time, first with only the plasma end connected, then with the other end connected to whatever it normally connects to.


You may find that the solution lies in one or all of the following:


Make sure that the plasma chassis is properly grounded with a 3 wire power cord that connects to a good ground.


Make sure that the equipment that the plasma connects to is well grounded with a 3 wire power cord that connects to the same ground as the plasma.


Make sure that the subwoofer well grounded with a 3 wire power cord that connects to the same ground as the plasma.


If any or all of these components don't have three wire power cords, try adding a ground wire that connects to an existing screw on each chassis to properly ground them.


If the cables were making it worse, make sure that you are using high quality signal cables for anything connecting to the plasma.


If the cables make the problem worse and quality cables doesn't help, you want to try modifying the signal cables to disconnect (lift) the ground (shield) on the plasma end of the cables. This may seem counter intuitive, but because they are already grounded at the signal end, grounding at both ends in not necessary and it can cause problems.


You could experiment with reversing the hot and neutral connectors on the plasma power cord to see if that helps.


You can also experiment with reversing the hot and neutral connectors on the subwoofer power cord to see if that helps.


You may want to try running the plasma and/or the subwoofer on an isolation transformer to see if that helps


Here is some interesting reading..


http://www.middleatlantic.com/resour...te-papers.aspx


http://jensen-transformers.com/apps_wp.html


Good luck!
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post #23 of 27 Old 11-18-2014, 09:16 PM
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Quote:
Originally Posted by DaveClement View Post
If I am understanding correctly, the subs are picking up this hum without any inputs connected to them. In other words, they are connected to power only? Is that correct? It sounds like your plasma TV is generating interference that is being fed through the AC power cord into the power system and then through the power cord into the subwoofer.


The fact that plugging the plasma into a different circuit eliminates the noise backs this up.


It may be that your plasma is producing more noise than it should, and/or it may be that your subwoofer is more susceptible to noise than it should be.


Does the plasma being on and displaying all white generate noise in any other components?


You say that you get a very slight hum in the subwoofer. Does it change when plugging it into a different power circuit and/or when you remove the input cables? It may be that the subwoofer always produces a little noise, or if it happens only when the input cables are connected, it could be a ground loop. But this does not sound like your main problem.


The fact that sound hits a null every 8 seconds or so leads me to believe that the problem is tied to the plasma's sync rate, which will be different than the 60 Hz power frequency. Video and computer resolutions are typically based on a "60 Hz" timing that is actually "59.94 Hz". As this goes in and out of phase with the power frequency it will get louder and quieter.


Try feeding the plasma a signal with a different refresh rate. Use a computer as a source (ideally a laptop running on a battery to eliminate any concerns with ground loops). Try changing to different resolutions with different scan rates to see if the interference changes. If it does, that is a pretty good indicator that the circuitry in the plasma is generating the interference. The fact that it happens most when the plasma is displaying a bright white screen certainly points in this direction. That's when all the pixels are lit up, the plasma is working the hardest and there would be the most potential for noise generation.


It sounds like you have already done this, but if not, try unplugging all input cables from the plasma end of the cable (as opposed to the signal end). If this helps, they were likely acting as antennas and radiating the interference. Try connecting each cable one at a time, first with only the plasma end connected, then with the other end connected to whatever it normally connects to.


You may find that the solution lies in one or all of the following:


Make sure that the plasma chassis is properly grounded with a 3 wire power cord that connects to a good ground.


Make sure that the equipment that the plasma connects to is well grounded with a 3 wire power cord that connects to the same ground as the plasma.


Make sure that the subwoofer well grounded with a 3 wire power cord that connects to the same ground as the plasma.


If any or all of these components don't have three wire power cords, try adding a ground wire that connects to an existing screw on each chassis to properly ground them.


If the cables were making it worse, make sure that you are using high quality signal cables for anything connecting to the plasma.


If the cables make the problem worse and quality cables doesn't help, you want to try modifying the signal cables to disconnect (lift) the ground (shield) on the plasma end of the cables. This may seem counter intuitive, but because they are already grounded at the signal end, grounding at both ends in not necessary and it can cause problems.


You could experiment with reversing the hot and neutral connectors on the plasma power cord to see if that helps.


You can also experiment with reversing the hot and neutral connectors on the subwoofer power cord to see if that helps.


You may want to try running the plasma and/or the subwoofer on an isolation transformer to see if that helps


Here is some interesting reading..


http://www.middleatlantic.com/resour...te-papers.aspx


http://jensen-transformers.com/apps_wp.html


Good luck!
Thanks for the reply Dave.

The buzz is carried to the sub through it's power cable if plugged into the same circuit as the TV because if I run an extension cable from the kitchen and plug the sub into that, the buzzing is completely gone.

Also it doesn't matter if the subwoofer audio cable is connected or disconnected. As long as it is on the same circuit as the TV, it buzzes. Also if I lift the ground on the sub itself and even use a cheater plug it still buzzes if on the same circuit as the TV. So there is some interference going through the actual power cable.

Is my only option to have an electrician come install a second circuit into my living room?
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post #24 of 27 Old 11-19-2014, 10:38 AM
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Is my only option to have an electrician come install a second circuit into my living room?

Absolutely not your only option.



The best option would be to give a call to to Jensen Transformers (818) 374-5857 and ask to speak to Dave or Bill (VP, and pres). I worked with them on a hum I was getting on my subs (i am using a 240VAC FP14000). We determined their SUB-2RR would resolve my hum issue and how right they were! Problem solved! They have solutions for most any stray noise issue you may have in an AV setup so give them a call. It's free and so is their advice.


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Absolutely not your only option.
I agree. Calling Jensen Transformers sounds like a great idea.


The more troubleshooting you can do, the more you will understand the problem and the more options you will have.


See the portion of my last thread that says "You may find that the solution lies in one or all of the following:.."
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post #26 of 27 Old 11-19-2014, 12:33 PM
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Absolutely not your only option.



The best option would be to give a call to to Jensen Transformers (818) 374-5857 and ask to speak to Dave or Bill (VP, and pres). I worked with them on a hum I was getting on my subs (i am using a 240VAC FP14000). We determined their SUB-2RR would resolve my hum issue and how right they were! Problem solved! They have solutions for most any stray noise issue you may have in an AV setup so give them a call. It's free and so is their advice.
The buzz I am getting is NOT travelling through the subwoofer audio cable. I know this because I can completely disconnect the audio cable from sub and it still buzzes exactly the same based on how hard the plasma TV is working to display a picture. Bright scenes buzz a lot more.

It is travelling through the subs power cord. My guess is there is some kind of backwash from the plasma TVs power supply that is traveling out the plasma TVs power cord and going into the sub through it's power cord because they are on the same circuit.

If I run a long extension cable from another circuit and plug the sub into that, it completely stops the buzz.

That makes sense to me, because the plasma TV is no longer on the same circuit and therefore not polluting the sub.
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post #27 of 27 Old 11-19-2014, 12:40 PM
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I had this same issue with my sub when it was plugged into the same circuit as my receiver. I ended up runnin an extension cord along the wall under the carpet to a different outlet on a different circuit and it fixed the issue just like your experience. Not real helpful since you don't have an outlet close, but I feel your pain.
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