Newsgroups: rec.audio.tech
Subject: Re: Grounding problem: More information
References: <[email protected]>
Mark Hansen  writes:

> Sorry not to follow-up to my previous posting, but it's been expired
> by the news server (after only 4 days ;-(
> 
> I have a Pioneer D2S A/V receiver and have been having a problem
> with a 60Hz hum on the center channel speaker whenever I have the
> unit in a ProLogic mode.
> 
> I have various components connected to the system, which include 2
> RG-6 coax cables (one for Satellite and one for the roof antenna).
> 
> When I disconnect each, there is no change. The hum remains until I
> disconnect the audio cable connecting the receiver to the sub woofer.
> 
> The Sub woofer contains a grounding (3-prong) plug.

You have a traditional ground loop problem caused by the 
groudn connections through both subwoofer ground and antenna network
groudn which are at different potential. Using suitable antenna isolator
in antenna connection should help. You can check if this works
by removing all antenna connections -> hum should be gone -> if this worked
go and buy the antenna isolators.

Also if you have more than one components connected to grounded
outlet, please be sure that they get power from the same power outlet
(to avidn ground loop between teo different electrical outlets).

For more information (both technical information and some product links) at
http://documents.epanorama.net/documents/groundloop/index.html

> When I connect a separate ground wire to a grounding lug on the
> receiver, the hum get noticeably worse.
>  
> When I disconnect the RCA cable at the sub woofer end, the hum
> is gone - with or without the ground wire connected to the
> receiver's grounding lug.

Very typical for ground loops that this kind of things happen..

> At this point, the antenna cables are out of the picture, 

Why ? Have you had all of them removed while testing. 
Properly grounded antenna connections can cause ground loop 
problem problems to audio equipment. And they are known to do
this very often. 

Combining more than one "properly grounded" system to your audio/video
system is known to cause more or less noise problems. 
The "properly grounded" for antenna network and electrical wiring means
that they are safe and those systems work on their own. 
They do not guarantee a noise-free operation of sensitive equipment
like your audio amplifier.

> except
> that one of them is not currently grounded, and I want to correct
> that. However, I'm guess that once I do, I'll re-introduce the
> Hum (when the sub woofer is connected).

The advice is to get everything that needs to be grounded to be
properly grounded. This is promarily for safety. Then if noise 
problems exist, then use signal isolators in the system to solve 
the ground loop problems.

> Is there anything I can do to resolve this? 

Yes. First read and understand 
http://documents.epanorama.net/documents/groundloop/index.html

It has the answers in it. Unfortunately there are no simple 
"works for all" solutions to this type of problems. To solve 
this kind of problems effectively you need to know what causes 
then and know the possible solvint techniques. Then you go to 
analyze your system (make a plot of it and measurements if needed), 
plan the postnetial solutions and try them. This is the tried 
process that gives good results.

> Can I run a ground wire between the receiver and the sub woofer? 

Yes. Already there is a wire which does grounding: the audio cable
shield. If you run an extra wire in parallel with it, it is 
effectively almost the same as you would have have an audio cable 
with more copper on the cable shield. This kind of extra wire can 
reduce the problem quite often, but very rarely removes it completely. 
In some cases adding that extra wire can make the problem even
worse. 

Audio signal isolators are the more effective solitions in this 
kind of cases thn thicn grounding wires.

> Would that be dangerous, given there is some current between those 
> two grounds?

There is already a nocticable current flowing through the audio cable
shield. Adding extra wires will increase the current somewhat, but 
quite rarely makes things daneground (but keep in mind that is possible 
if there is somethign wring in the house grounding practices).

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/