ground-loop problems

  • Thread starter William Sommerwerck
  • Start date
OK, then give it a try in 1080i and see if you still have the loop.
Click to expand...
It's impractical, because my component-video cables aren't long enough to
allow me to connect to the monitor while the Blu-ray player remains
connected to the audio system.

I have some other tests to run, and some people to talk with about ground
loops in general, and my system in particular. I will eventually report
back.

It's almost impossible to find cable isolation transformers. PartsExpress
sells one, but specifically states it's not suitable for digital signals
(presumably because it doesn't work well at the frequencies digital is
transmitted on). Comcast doesn't stock any, as they state very few customers
claim to have problems. I might buy two baluns, wire them together, and see
what happens.
 
In article <h108sa$e87$1@news.eternal-september.org>,
William Sommerwerck <grizzledgeezer@comcast.net> wrote:
OK, then give it a try in 1080i and see if you still have the loop.

It's impractical, because my component-video cables aren't long enough
to allow me to connect to the monitor while the Blu-ray player remains
connected to the audio system.

I have some other tests to run, and some people to talk with about
ground loops in general, and my system in particular. I will eventually
report back.

It's almost impossible to find cable isolation transformers.
PartsExpress sells one, but specifically states it's not suitable for
digital signals (presumably because it doesn't work well at the
frequencies digital is transmitted on). Comcast doesn't stock any, as
they state very few customers claim to have problems. I might buy two
baluns, wire them together, and see what happens.
Click to expand...
Has the Blue-ray player and or the TV - you're not quite clear if it's
only when both of these are used - got a three pin mains lead with a
connected ground? Have you tried unplugging the TV aerial (and perhaps
cable etc) connections - and then play a DVD?

--
*Generally speaking, you aren't learning much if your lips are moving.*

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
 
Has the Blue-ray player and or the TV -- you're not quite clear
if it's only when both of these are used -- got a three pin mains
lead with a connected ground? Have you tried unplugging the
TV aerial (and perhaps cable etc) connections -- and then play
a DVD?
Click to expand...
The buzz seems to occur only when the BD player and the TV are connected
with the HDMI cable. As I explained in the original post, (1) putting an
isolation transformer on the BD player, (2) lifting the player's ground &
reversing the plug, and (3) disconnecting the Motorola's power cord and HDMI
cable produces the lowest level of buzz.

What I have not checked if whether disconnecting /only/ the cable equipment
removes the buzz. I should have checked this earlier.
 
William Sommerwerck wrote:

Has the Blue-ray player and or the TV -- you're not quite clear
if it's only when both of these are used -- got a three pin mains
lead with a connected ground? Have you tried unplugging the
TV aerial (and perhaps cable etc) connections -- and then play
a DVD?


The buzz seems to occur only when the BD player and the TV are connected
with the HDMI cable. As I explained in the original post, (1) putting an
isolation transformer on the BD player, (2) lifting the player's ground &
reversing the plug, and (3) disconnecting the Motorola's power cord and HDMI
cable produces the lowest level of buzz.

What I have not checked if whether disconnecting /only/ the cable equipment
removes the buzz. I should have checked this earlier.
Click to expand...
In case you have not already found this document, get this pdf (don't try
to open it in a browser, download it):

http://www.wolfvid.com/datasheets/!OPERATOR_HANDBOOK_vidasst.pdf

It has quite an informative collection of electrical grounding advice
and horror stories, and data sheets on some products including the
"iso-max" isolation transformer. It's a long read, but worth plowing
through (apologies to Mr. Plowman).

Michael
 
On Sat, 13 Jun 2009 20:43:41 -0500, msg <msg@_cybertheque.org_> wrote:


In case you have not already found this document, get this pdf (don't try
to open it in a browser, download it):

http://www.wolfvid.com/datasheets/!OPERATOR_HANDBOOK_vidasst.pdf

It has quite an informative collection of electrical grounding advice
Click to expand...
A difficult read - but seems to have a reasonable deinition of a grounding
loop:-
"A ground loop is caused when two pieces of equipment are each hooked to ground
(through their power plugs) and are also connected together by a shielded audio
or video cable. All grounds are not created equal and there will be a difference
in voltage between the two ends of the shielded cable. This induces large
currents that get into all the equipment. The trick is to break one of the
ground connections, so that the cable shield does not carry any ground loop
current."

--
Geo
 
In article <e5h935dkjtu7k3qmrjgjlcancqj2ime0o3@4ax.com>,
Geo <hw9j-s5hw@dea.spamcon.org> wrote:
"A ground loop is caused when two pieces of equipment are each hooked to
ground (through their power plugs) and are also connected together by a
shielded audio or video cable. All grounds are not created equal and
there will be a difference in voltage between the two ends of the
shielded cable. This induces large currents that get into all the
equipment. The trick is to break one of the ground connections, so that
the cable shield does not carry any ground loop current."
Click to expand...
Indeed. Nothing magical at all. Of course not all hum is caused by a earth
loop.

--
*It was recently discovered that research causes cancer in rats*

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
 
On Sat, 13 Jun 2009 06:16:32 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

OK, then give it a try in 1080i and see if you still have the loop.

It's impractical, because my component-video cables aren't long enough to
allow me to connect to the monitor while the Blu-ray player remains
connected to the audio system.

I have some other tests to run, and some people to talk with about ground
loops in general, and my system in particular. I will eventually report
back.

It's almost impossible to find cable isolation transformers. PartsExpress
sells one, but specifically states it's not suitable for digital signals
(presumably because it doesn't work well at the frequencies digital is
transmitted on). Comcast doesn't stock any, as they state very few customers
claim to have problems. I might buy two baluns, wire them together, and see
what happens.
Click to expand...
Well I was just kinda curious if it was a problem specific to the HDMI
cable itself. I don't know what freq Comcast nodes uses but I'd guess
they are still in the 500mhz range. RR here uses 500, some others use
700 and the newest design by Cisco is 1 ghz. Check the freq range of
the isolators and remember that even an F connector has a 4db drop in
signal across it.
 
"Meat Plow" <meat@petitmorte.net> wrote in message
news:2svsrk.6mn.19.5@news.alt.net...
On Sat, 13 Jun 2009 06:16:32 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net>wrote:

Well I was just kinda curious if it was a problem specific
to the HDMI cable itself?
Click to expand...
Any ideas what they might be? (I'm not an HDMI expert.) It's a Belkin. I
have a No-Name-O I could try.
 
William Sommerwerck wrote:
OK, then give it a try in 1080i and see if you still have the loop.

It's impractical, because my component-video cables aren't long enough to
allow me to connect to the monitor while the Blu-ray player remains
connected to the audio system.

I have some other tests to run, and some people to talk with about ground
loops in general, and my system in particular. I will eventually report
back.

It's almost impossible to find cable isolation transformers. PartsExpress
sells one, but specifically states it's not suitable for digital signals
(presumably because it doesn't work well at the frequencies digital is
transmitted on). Comcast doesn't stock any, as they state very few customers
claim to have problems. I might buy two baluns, wire them together, and see
what happens.
Click to expand...

William, the way broadcast & recording studios in the US eliminate
ground loops is with 4" to 6" wide copper run between racks & consoles.
This is either silver soldered or brazed at the junctions to reduce the
ground system impedance. Soldering is the preferred method, but most
people can't solder 16 square inches of copper without burning a hole in
it. With a proper grounding system, it doesn't matter which phase or
breaker a piece of equipment is on.

http://www.gacopper.com/022-CopperStrap.html is an example of what is
used. Be advised that this method isn't cheap, but it is effective, and
doesn't degrade like other systems.


--
You can't have a sense of humor, if you have no sense!
 
I have some other tests to run, and some people to talk with
about ground loops in general, and my system in particular.
I will eventually report back.

William, the way broadcast & recording studios in the US eliminate
ground loops is with 4" to 6" wide copper run between racks & consoles.
This is either silver soldered or brazed at the junctions to reduce the
ground system impedance. Soldering is the preferred method, but most
people can't solder 16 square inches of copper without burning a hole in
it. With a proper grounding system, it doesn't matter which phase or
breaker a piece of equipment is on.
Click to expand...
This arrangement assumes the buss has such a low resistance that it forces
the equiment rounds to be at essentially the same AC potential, thus
reducing or eliminating ground loops. I have no doubt it works -- in a
studio.

I'm certain that if I made such a connection between my video+cable
equipment and my audio equipment, the problem would go away. But I'm not
sure exactly how to do it, especially as it's likely to cause my system to
look like Laocoon (et fils) and the sea serpents.

The closest I ever came to such a arrangement occurred in 1993, when I ran
cables across the floor from a JVC hall synthesizer to the power amp driving
the "side" speakers. There was quite a bit of hum. After some experimenting
I decided that the synthesizer's RCA output jacks weren't grounded
sufficiently to the chassis. So I ran a copper buss bar across the jacks and
soldered it solidly to the jacks and chassis ground. The hum went away.
 
On Sun, 14 Jun 2009 12:04:56 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

"Meat Plow" <meat@petitmorte.net> wrote in message
news:2svsrk.6mn.19.5@news.alt.net...
On Sat, 13 Jun 2009 06:16:32 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net>wrote:

Well I was just kinda curious if it was a problem specific
to the HDMI cable itself?

Any ideas what they might be? (I'm not an HDMI expert.) It's a Belkin. I
have a No-Name-O I could try.
Click to expand...
Not really, just tossing some suggestions out there. Only HDMI I have
is on a Sony upscaling DVD/VCR combo in the bedroom connected to a 32"
TV where both the audio and video are sent via the HDMI port.
 
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