Isolating PC from receiver to prevent ground loop

Isolating PC from receiver to prevent ground loop

Post by a.. » Wed, 13 Nov 2002 10:27:34



I recently moved my MP3 player PC from on top of my home entertainment
center (wife didn't like it there; go figure) to inside a cabinet in
the adjacent kitchen. I was so proud of the outlet and RCA jack
connections I installed to make everything nice and neat.

Unfortunately, I've created a problem ... the PC that houses my MP3
collection and player is now plugged into a different circuit, and
likely different phase, from my Denon receiver in the other room. A
loud ground hum is very obvious. I know that it is a ground hum
because I can unplug the PC from the outlet (so that it is running off
UPS), and there is no hum.

Without rewiring the outlet (it was a bear to find a circuit I could
tap into; long story), what clever ideas are there for getting rid of
the ground loop? Some way to opto-isolate it, for example. I thought
of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
it would only be transmitted a few inches), but then every time the
microwave oven is on, my sound is interfered with.

 
 
 

Isolating PC from receiver to prevent ground loop

Post by Bruce » Wed, 13 Nov 2002 11:36:49


Radio Shack sells a ground loop isolator (#270-054) that replaces the
RCA cable. It costs about $15. I've used it - it works.


Quote:> I recently moved my MP3 player PC from on top of my home entertainment
> center (wife didn't like it there; go figure) to inside a cabinet in
> the adjacent kitchen. I was so proud of the outlet and RCA jack
> connections I installed to make everything nice and neat.

> Unfortunately, I've created a problem ... the PC that houses my MP3
> collection and player is now plugged into a different circuit, and
> likely different phase, from my Denon receiver in the other room. A
> loud ground hum is very obvious. I know that it is a ground hum
> because I can unplug the PC from the outlet (so that it is running off
> UPS), and there is no hum.

> Without rewiring the outlet (it was a bear to find a circuit I could
> tap into; long story), what clever ideas are there for getting rid of
> the ground loop? Some way to opto-isolate it, for example. I thought
> of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
> it would only be transmitted a few inches), but then every time the
> microwave oven is on, my sound is interfered with.


 
 
 

Isolating PC from receiver to prevent ground loop

Post by Richard Malcolm-Smit » Fri, 15 Nov 2002 20:03:07



> Without rewiring the outlet (it was a bear to find a circuit I could
> tap into; long story), what clever ideas are there for getting rid of
> the ground loop? Some way to opto-isolate it, for example. I thought
> of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
> it would only be transmitted a few inches), but then every time the
> microwave oven is on, my sound is interfered with.

optical output? THat would sound better too..
 
 
 

Isolating PC from receiver to prevent ground loop

Post by Mark Lloy » Fri, 15 Nov 2002 22:47:13


On Fri, 15 Nov 2002 00:03:07 +1300, Richard Malcolm-Smith



>> Without rewiring the outlet (it was a bear to find a circuit I could
>> tap into; long story), what clever ideas are there for getting rid of
>> the ground loop? Some way to opto-isolate it, for example. I thought
>> of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
>> it would only be transmitted a few inches), but then every time the
>> microwave oven is on, my sound is interfered with.

You get a free "microwave in use" indicator.

Quote:>optical output? THat would sound better too..

--
41 days until the winter solstice celebration

Mark Lloyd
http://go.to/notstupid
http://notstupid.laughingsquid.com

"There's no more proof for the existence of God than there is for the existence of the
Easter Bunny. That's right. The Easter Bunny."

 
 
 

Isolating PC from receiver to prevent ground loop

Post by Chuc » Sat, 16 Nov 2002 03:25:02


What are the distance limits on digital optical cables? Can you run an
optical digital cable 50 feet? I thought about doing that from my PC
to my receiver, but I never could find any cables longer than about 12
feet.

I went with a 50 foot shielded RCA cable, and it sounds great. I was
careful about keeping the cable away from noise sources, and cross AC
lines at 90 degree angles. There is no audible hiss or hum at all!



> > Without rewiring the outlet (it was a bear to find a circuit I could
> > tap into; long story), what clever ideas are there for getting rid of
> > the ground loop? Some way to opto-isolate it, for example. I thought
> > of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
> > it would only be transmitted a few inches), but then every time the
> > microwave oven is on, my sound is interfered with.

> optical output? THat would sound better too..

 
 
 

Isolating PC from receiver to prevent ground loop

Post by no.spa » Sat, 16 Nov 2002 09:45:11


Is there a PC sound card with optical output?


>> Without rewiring the outlet (it was a bear to find a circuit I could
>> tap into; long story), what clever ideas are there for getting rid of
>> the ground loop? Some way to opto-isolate it, for example. I thought
>> of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
>> it would only be transmitted a few inches), but then every time the
>> microwave oven is on, my sound is interfered with.

>optical output? THat would sound better too..

 
 
 

Isolating PC from receiver to prevent ground loop

Post by Lewis Gardne » Sat, 16 Nov 2002 11:37:28


Here is an interesting product.

http://www.xitel.com/
http://www.etronics.com/product.asp?stk_code=xitprohifi

USB to toslink, coax digital and line level hiZ (RCA jack) audio gadget. I
have no idea if or how well it works but it does include 30'  cables.


> Is there a PC sound card with optical output?



> >> Without rewiring the outlet (it was a bear to find a circuit I could
> >> tap into; long story), what clever ideas are there for getting rid of
> >> the ground loop? Some way to opto-isolate it, for example. I thought
> >> of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
> >> it would only be transmitted a few inches), but then every time the
> >> microwave oven is on, my sound is interfered with.

> >optical output? THat would sound better too..

 
 
 

Isolating PC from receiver to prevent ground loop

Post by L. M. Rappapor » Mon, 18 Nov 2002 00:09:52



possible editing):

Quote:>I recently moved my MP3 player PC from on top of my home entertainment
>center (wife didn't like it there; go figure) to inside a cabinet in
>the adjacent kitchen. I was so proud of the outlet and RCA jack
>connections I installed to make everything nice and neat.

>Unfortunately, I've created a problem ... the PC that houses my MP3
>collection and player is now plugged into a different circuit, and
>likely different phase, from my Denon receiver in the other room. A
>loud ground hum is very obvious. I know that it is a ground hum
>because I can unplug the PC from the outlet (so that it is running off
>UPS), and there is no hum.

>Without rewiring the outlet (it was a bear to find a circuit I could
>tap into; long story), what clever ideas are there for getting rid of
>the ground loop? Some way to opto-isolate it, for example. I thought
>of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
>it would only be transmitted a few inches), but then every time the
>microwave oven is on, my sound is interfered with.

A possible easy solution would be to find the breaker that feeds the
circuit and see if you can swap it one position up or down with either
neighbor.

--
Larry

 
 
 

Isolating PC from receiver to prevent ground loop

Post by a.. » Mon, 18 Nov 2002 00:29:47


That sounds like a possibility. I will test to see if that will be
sufficient by running an extension cord from an outlet on the same
phase as the receiver to see if that fixes it. If so, I'll swap the
breakers.

But not to sound ignorant, but I thought the breakers on the left side
were one phase, and right side were the other. No? So I'd have to swap
breakers (and there output) that were on opposite sides of the box
rather than one up or down. Am I wrong? [If it matters, it's a pretty
standard residential Square D box from 1985; ones where the breakers
do have a tripped indicator in a little window).



>possible editing):

>>I recently moved my MP3 player PC from on top of my home entertainment
>>center (wife didn't like it there; go figure) to inside a cabinet in
>>the adjacent kitchen. I was so proud of the outlet and RCA jack
>>connections I installed to make everything nice and neat.

>>Unfortunately, I've created a problem ... the PC that houses my MP3
>>collection and player is now plugged into a different circuit, and
>>likely different phase, from my Denon receiver in the other room. A
>>loud ground hum is very obvious. I know that it is a ground hum
>>because I can unplug the PC from the outlet (so that it is running off
>>UPS), and there is no hum.

>>Without rewiring the outlet (it was a bear to find a circuit I could
>>tap into; long story), what clever ideas are there for getting rid of
>>the ground loop? Some way to opto-isolate it, for example. I thought
>>of using a 2.4 GHz transmitter thing (X10) to transmit the audio (and
>>it would only be transmitted a few inches), but then every time the
>>microwave oven is on, my sound is interfered with.

>A possible easy solution would be to find the breaker that feeds the
>circuit and see if you can swap it one position up or down with either
>neighbor.

 
 
 

Isolating PC from receiver to prevent ground loop

Post by Terry Kin » Mon, 18 Nov 2002 00:45:36


In most (Maybe all) panels, phases alternate so that a two-circuit
230V breaker can pick up alternate phases.

Quote:> I thought the breakers on the left side
> were one phase, and right side were the other. No? So I'd have to swap
> breakers (and there output) that were on opposite sides of the box
> rather than one up or down.

--
Regards, Terry King ...In The Woods In Vermont

 
 
 

Isolating PC from receiver to prevent ground loop

Post by st.. » Mon, 18 Nov 2002 05:35:48


Ah! Of course .. that there are double-size breakers for 220 circuits
on the same side should have been a clue for the clueless. Thanks.

>In most (Maybe all) panels, phases alternate so that a two-circuit
>230V breaker can pick up alternate phases.
>> I thought the breakers on the left side
>> were one phase, and right side were the other. No? So I'd have to swap
>> breakers (and there output) that were on opposite sides of the box
>> rather than one up or down.

 
 
 

Isolating PC from receiver to prevent ground loop

Post by a.. » Mon, 18 Nov 2002 07:31:27


Good thing I tested it before bothering to move the breakers around ..
when the PC and the receiver are plugged into the same outlet, the
ground loop still exists. Yes, running the PC off UPS fixes the
problem. Huh.

Looks like I'll either go with the Radio Shack devise, look for a
sound card with optical output, or get one of the devices below.

Thanks all for the help.

Here is an interesting product.

http://www.xitel.com/
http://www.etronics.com/product.asp?stk_code=xitprohifi

 
 
 

Isolating PC from receiver to prevent ground loop

Post by Larry Nielse » Mon, 18 Nov 2002 11:37:12


Quote:> A possible easy solution would be to find the breaker that feeds the
> circuit and see if you can swap it one position up or down with either
> neighbor.

Ooops.  Careful here.  Frequently the wiring will have two circuits on
opposite legs sharing one neutral.  When the load on each circuit is
balanced, for example (up to) the full 15 amps each, they are in series and
cancel and therefore there is no current in the neutral.  If the loads are
not the same, the difference is carried by the neutral.  Obviously, that
difference can never be more than one full load even with on of the circuit
loads at zero.

If you move only one of these circuits it ends up being on the same leg as
the other circuit.  Now the loads on each circuit (up to)15 amps EACH are
added and both are carried by the neutral instead of canceling, i.e.; (up
to) 30 amps.  A big no no.

If the circuit in question has its own home-run-neutral not shared with any
other circuits it will be OK to move it to either leg.

Regards,  Larry Nielsen

 
 
 

Isolating PC from receiver to prevent ground loop

Post by L. M. Rappapor » Tue, 19 Nov 2002 00:29:28


On Sat, 16 Nov 2002 21:37:12 -0500, "Larry Nielsen"

Quote:>> A possible easy solution would be to find the breaker that feeds the
>> circuit and see if you can swap it one position up or down with either
>> neighbor.

>Ooops.  Careful here.  Frequently the wiring will have two circuits on
>opposite legs sharing one neutral.  When the load on each circuit is
>balanced, for example (up to) the full 15 amps each, they are in series and
>cancel and therefore there is no current in the neutral.  If the loads are
>not the same, the difference is carried by the neutral.  Obviously, that
>difference can never be more than one full load even with on of the circuit
>loads at zero.

>If you move only one of these circuits it ends up being on the same leg as
>the other circuit.  Now the loads on each circuit (up to)15 amps EACH are
>added and both are carried by the neutral instead of canceling, i.e.; (up
>to) 30 amps.  A big no no.

>If the circuit in question has its own home-run-neutral not shared with any
>other circuits it will be OK to move it to either leg.

>Regards,  Larry Nielsen

Larry,

        A good point, but (and I could very well be wrong here) wiring
two circuits with x/3 was never code-approved.   That said, it does
work exactly as you explained and isn't dangerous UNLESS you move a
breaker as I had suggested.  Good heads up.

        Now, to the fellow who posted the original problem.  The
common reason for this problem is that on the input of the power
section of one of those two devices (or perhaps both), there will be
some bypass capacitors.  Normally they are .01 mfd or smaller disc
ceramics and they go from each side of the line (sometimes through a
choke) to ground.  They will usually be rated at 600v or so.  One of
them is leaking.  If you feel comfortable replacing  them, they are
cheap.  Here we'd just replace all of them.  

        Using an isolation transformer, as others have suggested, is
easier and will work fine, but replacing the bypass capacitors is
cheaper.  

        Good luck,

--
Larry

 
 
 

Isolating PC from receiver to prevent ground loop

Post by Larry Nielse » Tue, 19 Nov 2002 01:31:09


Quote:> A good point, but (and I could very well be wrong here) wiring
> two circuits with x/3 was never code-approved.

Umm, I don't think so Larry.  No claim here to knowing the code thoroughly
but I have seen plenty of new construction, recently too, where a conduit or
romex leaves the breaker box with three conductors.  One neutral and two
(opposite leg) hot wires.  It does exist frequently.

Do we have  anyone listening that knows the code for sure to comment?

Regards,  Larry

 
 
 

1. Grounding Leviton Switches/receivers

Can anyone confirm that the Leviton X-10 wall switches/receivers and
controllers meet the national electric code when installed? The reason for
the question is that there is no provision on the Leviton X-10 wall switches
and controllers to make a ground connection to the metal frame. The Leviton
standard wall switches have a grounding screw to ground the body of the
switch but the Levition X-10 gear have no provision to connect to ground.
Does this meet code?

I am wrapping up the electical portion of an addition to my house and want
to make sure the X-10 stuff meets code, rather than install std switches and
then replace with X-10 after inspection. I am using plastic work boxes so
the metal frames cannot connect to ground through the mounting screws.

Are they to code with no grounding of the metal frame?

Regards,
Doc

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