ground-loop problems

[William Sommerwerck]

This posting isn't intended to provoke hundreds of responses. Rather, I'm
looking for insights I've missed, that might be of use to both me and
others.

Everything in my main audio system _except_ the power amps are on the same
circuit. This hasn't caused problems, because the audio connections to the
power amps are balanced.

When I added a Sony BDP-550 Blu-ray player to the audio system (its analog
audio outputs feeding a Parasound C2 controller), plus a Pioneer plasma TV
on another AC circuit (or at least an outlet some distance away), I started
hearing a buzz in the speakers at "ordinary" gain levels. It was
particularly noticeable in the rear speakers when there was no audio signal
to mask them.

The first thing I did was to put the Blu-ray player on an isolation
transformer (that just happened to be lying around). That helped, but didn't
reduce the buzz as much as I would have liked.

For cable reception, the Pioneer plasma is fed from a Motorola decoder box
through an HDMI cable. Disconnecting the decoder from AC, and the HDMI from
the Pioneer plasma further reduces the buzz.

It's worth noting that, as you turn up the controller's volume to check the
buzz level, the buzz comes in abruptly at one point. Then, to get rid of the
hum, you have to turn the volume well below that point. This might be a
psychoacoustic illusion, but I doubt it. It seems more like some weird sort
of hysteresis. Is it a symptom that points to a cause?

It should come as no surprise that the only way to really suppress the buzz
is to disconnect the HDMI cable that connects the Blu-ray player to the
Pioneer plasma. Of course, you can't do that when watching Blu-ray movies!

It would be nice if I could simply leave everything connected all the time.
I've thought of connecting the plasma's AC to the main audio system's power
outlet with a very heavy (12ga) cord. But I'm not sure I want to add 400+
watts load to that outlet. *

Thoughts, please. Thank you.

* Even with the controller and several other components running, I'm drawing
less than 300 watts, so there's "room".

 

[Charles]

Sometimes it is instructive to "unground" a shielded audio cable at one end.

 

[Trevor Wilson]

This posting isn't intended to provoke hundreds of responses. Rather, I'm
looking for insights I've missed, that might be of use to both me and
others.

Everything in my main audio system _except_ the power amps are on the same
circuit. This hasn't caused problems, because the audio connections to the
power amps are balanced.

When I added a Sony BDP-550 Blu-ray player to the audio system (its analog
audio outputs feeding a Parasound C2 controller), plus a Pioneer plasma TV
on another AC circuit (or at least an outlet some distance away), I
started
hearing a buzz in the speakers at "ordinary" gain levels. It was
particularly noticeable in the rear speakers when there was no audio
signal
to mask them.

The first thing I did was to put the Blu-ray player on an isolation
transformer (that just happened to be lying around). That helped, but
didn't
reduce the buzz as much as I would have liked.

For cable reception, the Pioneer plasma is fed from a Motorola decoder box
through an HDMI cable. Disconnecting the decoder from AC, and the HDMI
from
the Pioneer plasma further reduces the buzz.

It's worth noting that, as you turn up the controller's volume to check
the
buzz level, the buzz comes in abruptly at one point. Then, to get rid of
the
hum, you have to turn the volume well below that point. This might be a
psychoacoustic illusion, but I doubt it. It seems more like some weird
sort
of hysteresis. Is it a symptom that points to a cause?

It should come as no surprise that the only way to really suppress the
buzz
is to disconnect the HDMI cable that connects the Blu-ray player to the
Pioneer plasma. Of course, you can't do that when watching Blu-ray movies!

It would be nice if I could simply leave everything connected all the
time.
I've thought of connecting the plasma's AC to the main audio system's
power
outlet with a very heavy (12ga) cord. But I'm not sure I want to add 400+
watts load to that outlet. *

Thoughts, please. Thank you.

* Even with the controller and several other components running, I'm
drawing
less than 300 watts, so there's "room".

**Disconnect the antenna/cable connection from the system. That should do
the trick. If it does, you need an isolator for the antenna/cable system.

 

[William Sommerwerck]

I take it the Blue device doesn't have a component out

that you could try instead of HDMI?

It does, but... I don't think it supports 1080p. And even if it did, I'd
still have a common ground, would I not?

This is not a major problem, just an irritation.

 

[William Sommerwerck]

Keep in mind that your balanced amps will not be balanced unless

whatever drives them has balanced outputs.

<extreme sarcasm>Gee. I never knew.</extreme sarcasm> The amps and the
controller are from the same company, and the balanced outputs of the
controller feeds the power amps.

Your cable TV is a common culprit for introducing hum, etc. Use a 75 ohm to
75 ohm transformer or back to back 75 to 300 ohm matching transformers if
the cable is adding hum when connected.

I am aware of this. I discovered it by myself 25 years ago.

 

[William Sommerwerck]

On Tue, 9 Jun 2009 08:48:55 -0700, "William Sommerwerck"

It supports 1080p, why else would it be there?

Because not everyone with a Blu-ray player necessarily has an HD set with
HDMI. By that reasoning, Blu-ray players should have only HDMI outputs. They
don't. They have a variety of outputs, to support varying resolutions and
"connectivity".

The component outputs on my Sony BDP-S550 DO NOT support 1080p.

http://www.sonystyle.com/wcsstore/SonyStyleStorefrontAssetStore/pdf/BDPS550_OM.pdf

They support 480p, 480i, 720p, 1080i. No higher. (See page 14.)

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

I have some other tests to run, and some people to talk with

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.

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.