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Ground Loop



 
 
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  #11  
Old October 27th 19, 02:55 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,649
Default Ground Loop

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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  #12  
Old October 27th 19, 04:59 PM posted to rec.audio.pro
Bob Simon[_2_]
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Posts: 12
Default Ground Loop

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?
  #13  
Old October 27th 19, 05:14 PM posted to rec.audio.pro
Bob Simon[_2_]
external usenet poster
 
Posts: 12
Default Ground Loop

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?
  #14  
Old October 27th 19, 05:17 PM posted to rec.audio.pro
Bob Simon[_2_]
external usenet poster
 
Posts: 12
Default Ground Loop

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?
  #15  
Old October 27th 19, 09:31 PM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 450
Default Ground Loop

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
  #16  
Old October 27th 19, 11:09 PM posted to rec.audio.pro
Phil Allison[_4_]
external usenet poster
 
Posts: 450
Default Ground Loop

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
  #17  
Old October 27th 19, 11:24 PM posted to rec.audio.pro
John Williamson
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Posts: 1,658
Default Ground Loop

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.
  #18  
Old October 27th 19, 11:26 PM posted to rec.audio.pro
Scott Dorsey
external usenet poster
 
Posts: 16,649
Default Ground Loop

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."
  #19  
Old October 28th 19, 01:29 AM posted to rec.audio.pro
Phil Allison[_4_]
external usenet poster
 
Posts: 450
Default Ground Loop

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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