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Bob Simon[_2_] Bob Simon[_2_] is offline
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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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Phil Allison[_4_] Phil Allison[_4_] is offline
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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

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geoff geoff is offline
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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

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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
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John Williamson John Williamson is offline
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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.


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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

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Scott Dorsey Scott Dorsey is offline
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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."
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Bob Simon[_2_] Bob Simon[_2_] is offline
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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.
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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
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Scott Dorsey Scott Dorsey is offline
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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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Scott Dorsey Scott Dorsey is offline
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Bob Simon wrote:
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 no=
t?


Maybe you have a different issue. Disconnect the cable. Does the hum stop?
If so, it's not the cable.

The isolation transformer should effectively stop any ground loop through the
cable system. But test it and make sure.

"Don't guess, measure."
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Bob Simon[_2_] Bob Simon[_2_] is offline
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On Sunday, October 27, 2019 at 8:55:36 AM UTC-5, Scott Dorsey wrote:
Bob Simon wrote:
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 no=
t?


Maybe you have a different issue. Disconnect the cable. Does the hum stop?
If so, it's not the cable.

The isolation transformer should effectively stop any ground loop through the
cable system. But test it and make sure.

"Don't guess, measure."
--scott

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


Scott,
Thanks! You were right! It had nothing to do with the cable feed. Following your advice to draw all the connections enabled me to identify the root cause.

I had forgotten that there is a high-level connection from the amp's main (speaker) outs to a powered subwoofer which was plugged into a different circuit. When I used a 3-wire extension cord to plug the sub into the power strip for the rest of the system, the hum went away. Now I have to figure out how to route an extension cord across the room in a way that my wife can tolerate. As an alternative, I wonder if an affordable power isolator exists for this type of issue. Are you aware of something suitable?
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Bob Simon[_2_] Bob Simon[_2_] is offline
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On Sunday, October 27, 2019 at 8:55:36 AM UTC-5, Scott Dorsey wrote:
Bob Simon wrote:
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 no=
t?


Maybe you have a different issue. Disconnect the cable. Does the hum stop?
If so, it's not the cable.

The isolation transformer should effectively stop any ground loop through the
cable system. But test it and make sure.

"Don't guess, measure."
--scott

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


Scott,
Thanks! You were right! It had nothing to do with the cable feed. Following your advice to draw all the connections enabled me to identify the root cause.

I had forgotten that there is a high-level connection from the amp's main (speaker) outs to a powered subwoofer which was plugged into a different circuit. When I used a 3-wire extension cord to plug the sub into the power strip for the rest of the system, the hum was reduced to a very low level. Now I have to figure out how to route an extension cord across the room in a way that my wife can tolerate. As an alternative, I wonder if an affordable power isolator exists for this type of issue so I won't need an extension cord (which adds resistance). Are you aware of something suitable?
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Bob Simon[_2_] Bob Simon[_2_] is offline
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On Sunday, October 27, 2019 at 8:55:36 AM UTC-5, Scott Dorsey wrote:
Bob Simon wrote:
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 no=
t?


Maybe you have a different issue. Disconnect the cable. Does the hum stop?
If so, it's not the cable.

The isolation transformer should effectively stop any ground loop through the
cable system. But test it and make sure.

"Don't guess, measure."
--scott

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


Scott,
Thanks! You were right! It had nothing to do with the cable feed. Following your advice to draw all the connections enabled me to identify the root cause.

I had forgotten that there is a high-level connection from the amp's main (speaker) outs to a powered subwoofer which was plugged into a different circuit. When I used a 3-wire extension cord to plug the sub into the power strip for the rest of the system, the hum was reduced to a very low level. Now I have to figure out how to route an extension cord across the room in a way that my wife can tolerate. As an alternative, I wonder if an affordable power isolator exists for this type of issue so I could eliminate the extension cord. Are you aware of something suitable?
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Phil Allison[_4_] Phil Allison[_4_] is offline
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Bob Simon 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.



I am the OP. John is correct - audio does not go to the TV,



** Read the fake quote.

See the words "nowhere near" ???

Since removing the ground from the TV stops the hum - it IS part of the earth loop the affects your AUDIO !!

which does not have an audio amp or speakers.


** Irrelevant to the earth loop issue.


So, to be precise, it's really just a video monitor rather than a TV.



** FFS get theat rubbish out of out head.

The entire system has a COMMON earth.


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.


** You are one dumb jerk.

ALL the items in your system are potential culprits in an earth loop scenario.

The only change I made to eliminate the hum was lifting the ground to the video monitor.


** So there was another ground someone - among the many items you failed to MENTION !!

Selecting your evidence STUFFS any attempt at giving you help.



...... Phil


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Bob Simon wrote:

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


I had forgotten that there is a high-level connection from the
amp's main (speaker) outs to a powered subwoofer which was plugged
into a different circuit. When I used a 3-wire extension cord to
plug the sub into the power strip for the rest of the system, the
hum was reduced to a very low level.


** With the TV still de-earthed ?

FYI:

Hum loops are caused by TWO separate things.

1. Different AC circuits being used with independent safety grounds with varying levels of stray AC voltage - generally only millivolts.

2. Magnetic field injection into a ground LOOP or loops formed by the various items in a system being connected to each other as well as a single safety ground.

The mag field comes from any power transformer inside a loop, so part of the equipment.

Picking a single item, usually the main or power amplifier, and making that be the ONLY safety grounded thing is the usual fix.

With a home entertainment system that includes a TV signal arriving at the premises from outside, that is another source of ground hum just like situation #1 described above. Hence using a balun isolator is normal practice.

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


As an alternative, I wonder if an affordable power isolator exists for this type of issue so I won't need an extension cord (which adds resistance). Are you aware of something suitable?

** Most folk just break the ground pin off the plug or fit a plug with no such pin. Neither is safe or legal.

I know how to modify items to eliminate the problem safely, but it would not meet regulations so a device that did the same cannot go on sale.

For the curious - it involves fitting a 25amp bridge in series with the safety ground conductor. This allow the item to float up to a volt or so above ground with NO current flow.

The bridge is wired as pairs of inverse parallel diodes and can cope with a massive fault current if need be until a fuse blows or a supply breaker trips.

My workbench scope has this scheme fitted inside, for example.


..... Phil
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On 27/10/2019 22:09, Phil Allison wrote:

For the curious - it involves fitting a 25amp bridge in series with the safety ground conductor. This allow the item to float up to a volt or so above ground with NO current flow.

The bridge is wired as pairs of inverse parallel diodes and can cope with a massive fault current if need be until a fuse blows or a supply breaker trips.

My workbench scope has this scheme fitted inside, for example.


Similar items are sold as galvanic isolators for boats connected to a
shore supply. The diodes in the one I use are rated at 2000Amps for long
enough for the fuse to blow.
--
Tciao for Now!

John.
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Scott Dorsey Scott Dorsey is offline
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Bob Simon wrote:
I had forgotten that there is a high-level connection from the amp's main (=
speaker) outs to a powered subwoofer which was plugged into a different cir=
cuit. When I used a 3-wire extension cord to plug the sub into the power s=
trip for the rest of the system, the hum went away. Now I have to figure o=
ut how to route an extension cord across the room in a way that my wife can=
tolerate. As an alternative, I wonder if an affordable power isolator exi=
sts for this type of issue. Are you aware of something suitable?


Don't break power line grounds. Break signal grounds. In the pro audio
world we use balanced connections which make this easy. With consumer gear
you will need an isolation transformer to do the same thing. The cheap
Edcor stuff will likely be fine for you.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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John Williamson wrote:

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


For the curious - it involves fitting a 25amp bridge in series
with the safety ground conductor. This allow the item to float up
to a volt or so above ground with NO current flow.

The bridge is wired as pairs of inverse parallel diodes and can
cope with a massive fault current if need be until a fuse blows
or a supply breaker trips.

My workbench scope has this scheme fitted inside, for example.



Similar items are sold as galvanic isolators for boats connected to a
shore supply. The diodes in the one I use are rated at 2000Amps for long
enough for the fuse to blow.


** Typical mag thermal breakers trip in under 1mS.

The diodes in a 25A bridge are rated for 300amps for a half cycle or 8ms.

AFAIK, power supply on a wharf is normally 3 phase for medium and large boats.

I guess a single phase outlet is also available with it own breaker.

In any case, diodes fail short, so safely in this case.



...... Phil


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