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Ground Loop



 
 
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  #1  
Old October 27th 19, 03:50 AM posted to rec.audio.pro
Bob Simon[_2_]
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Posts: 14
Default Ground Loop

My Panasonic TV (TH-50PH9UK) is a video monitor only; all audio is routed through my NAD preamp and amp. Last week, a hum started without having made any changes to any systems. Today, I tried unsuccessfully to eliminated it by plugging the TV into the same power strip that the preamp and amp are plugged into. Lifting the TV's ground eliminated the hum.

Does this suggest that a capacitor shorted last week in the amp, preamp, or TV?

As a practical matter, have I created an unsafe or inappropriate condition by lifting the TV's ground pin?
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  #2  
Old October 27th 19, 04:34 AM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default Ground Loop

Bob Simon wrote:

-----------------

> My Panasonic TV (TH-50PH9UK) is a video monitor only;
> all audio is routed through my NAD preamp and amp.
> Last week, a hum started without having made any changes to any systems.
>


** That makes no sense - how do you get a TV pic.

You have no cable or antenna connection ?



..... Phil

  #3  
Old October 27th 19, 05:27 AM posted to rec.audio.pro
geoff
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Posts: 1,546
Default Ground Loop

On 27/10/2019 4:34 pm, Phil Allison wrote:
> Bob Simon wrote:
>
> -----------------
>
>> My Panasonic TV (TH-50PH9UK) is a video monitor only;
>> all audio is routed through my NAD preamp and amp.
>> Last week, a hum started without having made any changes to any systems.
>>

>
> ** That makes no sense - how do you get a TV pic.
>
> You have no cable or antenna connection ?
>
>
>
> .... Phil
>


You must have missed the bit "My Panasonic TV (TH-50PH9UK) is a video
monitor only" !

geoff

  #4  
Old October 27th 19, 06:26 AM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default Ground Loop

geoff the Kiwi Jerk wrote:

---------------------------

>
> >> My Panasonic TV (TH-50PH9UK) is a video monitor only;
> >> all audio is routed through my NAD preamp and amp.
> >> Last week, a hum started without having made any changes to any systems.
> >>

> >
> > ** That makes no sense - how do you get a TV pic.
> >
> > You have no cable or antenna connection ?
> >
> >
>> >

>
> You must have missed the bit "My Panasonic TV (TH-50PH9UK) is a video
> monitor only" !
>



** Nup, a TV set can be a monitor with a digital STB plus antenna or cable box supplying the video.

Important to know, as those are prime causes of hum loops.



..... Phil
  #5  
Old October 27th 19, 08:30 AM posted to rec.audio.pro
John Williamson
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Posts: 1,659
Default Ground Loop

On 27/10/2019 05:26, Phil Allison wrote:
> geoff wrote:
>> You must have missed the bit "My Panasonic TV (TH-50PH9UK) is a video
>> monitor only" !
>>

>
>
> ** Nup, a TV set can be a monitor with a digital STB plus antenna or cable box supplying the video.
>
> Important to know, as those are prime causes of hum loops.
>

The OP also states that the audio goes nowhere near the monitor.

Tciao for Now!

John.
  #6  
Old October 27th 19, 12:41 PM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default Ground Loop

John Williamson wrote:

---------------------------

>> You must have missed the bit "My Panasonic TV (TH-50PH9UK) is a video
> >> monitor only" !
> >>

> >
> >
> > ** Nup, a TV set can be a monitor with a digital STB plus antenna
> > or cable box supplying the video.
> >
> > Important to know, as those are prime causes of hum loops.
> >

>
> The OP also states that the audio goes nowhere near the monitor.
>


** Fake quote - just like fake news.

Complete bull****.

Ask Mr Trump.




..... Phil

  #7  
Old October 27th 19, 02:02 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,655
Default Ground Loop

Bob Simon > wrote:
>My Panasonic TV (TH-50PH9UK) is a video monitor only; all audio is routed t=
>hrough my NAD preamp and amp. Last week, a hum started without having made=
> any changes to any systems. Today, I tried unsuccessfully to eliminated i=
>t by plugging the TV into the same power strip that the preamp and amp are =
>plugged into. Lifting the TV's ground eliminated the hum.


The TV has multiple grounds. That's the problem. Likely what you mean is
"lifting the TV's power line safety ground."

>Does this suggest that a capacitor shorted last week in the amp, preamp, or=
> TV?


No, it suggests that the grounding system on the cable TV line has likely
changed, since this is the most common source of these problems.

>As a practical matter, have I created an unsafe or inappropriate condition =
>by lifting the TV's ground pin?


Yes, totally. They don't call it a "safety ground" for nothing. Isolate
the ground on the cable TV line, not on the power line.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #8  
Old October 27th 19, 02:06 PM posted to rec.audio.pro
Bob Simon[_2_]
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Posts: 14
Default Ground Loop

On Sunday, October 27, 2019 at 6:41:20 AM UTC-5, Phil Allison wrote:
> John Williamson wrote:
>
> ---------------------------
>
> >> You must have missed the bit "My Panasonic TV (TH-50PH9UK) is a video
> > >> monitor only" !
> > >>
> > >
> > >
> > > ** Nup, a TV set can be a monitor with a digital STB plus antenna
> > > or cable box supplying the video.
> > >
> > > Important to know, as those are prime causes of hum loops.
> > >

> >
> > The OP also states that the audio goes nowhere near the monitor.
> >

>
> ** Fake quote - just like fake news.
>
> Complete bull****.
>
> Ask Mr Trump.
>
>
>
>
> .... Phil


I am the OP. John is correct - audio does not go to the TV, which does not have an audio amp or speakers. So, to be precise, it's really just a video monitor rather than a TV.

Yes, of course there are other devices that indirectly connect to both the audio system and the monitor. A Contour STB, BluRay player, and Fire Stick are all connected to an iArk 3-port HDMI switch with the output going to the monitor. 2-channel audio from this switch goes to the pre-amp as well as audio from the STB and BleRay player. The Cox feed to the STB is isolated using a Jensen ISO-MAX VRD-1FF CATV Isolator.

I did not include any information on these devices in my original post because the resolution of the hum issue did not involve them. The only change I made to eliminate the hum was lifting the ground to the video monitor.

In troubleshooting, I found that I could eliminate the hum by either disconnecting the HDMI cable from the HDMI switch to the TV or unplugging the three devices from the pre-amp. None of these configurations are useful but they led me to lifting the monitor's ground.
  #9  
Old October 27th 19, 02:24 PM posted to rec.audio.pro
Bob Simon[_2_]
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Posts: 14
Default Ground Loop

On Sunday, October 27, 2019 at 8:02:04 AM UTC-5, Scott Dorsey wrote:
> Bob Simon > wrote:
> >My Panasonic TV (TH-50PH9UK) is a video monitor only; all audio is routed t=
> >hrough my NAD preamp and amp. Last week, a hum started without having made=
> > any changes to any systems. Today, I tried unsuccessfully to eliminated i=
> >t by plugging the TV into the same power strip that the preamp and amp are =
> >plugged into. Lifting the TV's ground eliminated the hum.

>
> The TV has multiple grounds. That's the problem. Likely what you mean is
> "lifting the TV's power line safety ground."
>
> >Does this suggest that a capacitor shorted last week in the amp, preamp, or=
> > TV?

>
> No, it suggests that the grounding system on the cable TV line has likely
> changed, since this is the most common source of these problems.
>
> >As a practical matter, have I created an unsafe or inappropriate condition =
> >by lifting the TV's ground pin?

>
> Yes, totally. They don't call it a "safety ground" for nothing. Isolate
> the ground on the cable TV line, not on the power line.
> --scott
>
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."


Scott,
Thank you for your reply. Yes, I lifted the TV's safety ground.

The cable demarc is attached to the garage and is around 50' from the grounding rod for the electrical panel. The demarc has a separate grounding rod connected by some thin wire (perhaps 16 AWG). If I ground the demarc with 10 AWG solid copper wire and a brand new clamp, will that likely eliminate the multiple grounds issue?

I bought the Jensen ISOMAX years ago because I was told it would eliminate the cable ground issue. Apparently, it isn't. Do you have any idea why not?
Bob
  #10  
Old October 27th 19, 02:53 PM posted to rec.audio.pro
Scott Dorsey
external usenet poster
 
Posts: 16,655
Default Ground Loop

Bob Simon > wrote:
>Yes, of course there are other devices that indirectly connect to both the =
>audio system and the monitor. A Contour STB, BluRay player, and Fire Stick=
> are all connected to an iArk 3-port HDMI switch with the output going to t=
>he monitor. 2-channel audio from this switch goes to the pre-amp as well a=
>s audio from the STB and BleRay player. The Cox feed to the STB is isolate=
>d using a Jensen ISO-MAX VRD-1FF CATV Isolator.


So what changed with them?

>I did not include any information on these devices in my original post beca=
>use the resolution of the hum issue did not involve them. The only change =
>I made to eliminate the hum was lifting the ground to the video monitor. =


Every device needs to have one and only one ground path to everything else in
the system. If you have two paths, you get a hum. If you break either one
of those two paths, the hum stops.

Don't break the path that goes through the power line safety ground. Break
the other one. To do that, you have to find it, and that means drawing out
where all the grounds go and/or disconnecting things to see what things are
in the path of the loop.

>In troubleshooting, I found that I could eliminate the hum by either discon=
>necting the HDMI cable from the HDMI switch to the TV or unplugging the thr=
>ee devices from the pre-amp. None of these configurations are useful but t=
>hey led me to lifting the monitor's ground.


Draw it out on paper. Now you know that you have a loop through the HDMI cable
and through the preamp. Now you get to find which of the devices going into
the preamp has the parasitic ground.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
 




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