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

> Benny354 wrote:
> >>Subject: Grounding problem: More information
> >> From: Mark Hansen [email protected] Date: 9/14/2002 9:06 PM
> >> Eastern Standard Time
> >>Message-id: <[email protected]>
> >>
> >>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.
> >>
> >>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.
> >>
> >>At this point, the antenna cables are out of the picture, 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).
> >>
> >>Is there anything I can do to resolve this? Can I run a ground
> >>wire between the receiver and the sub woofer? Would that be
> >>dangerous, given there is some current between those two grounds?
> >>
> >>Thanks,
> >>
> > Cant help ya much. You sound like a smart person, so I wouldnt think
> > this would
> >  be the case but....
> > Maybe you didnt ground the adapter from the subwoofer electrical cord. You need
> > to screw that little tab on the adapter into the wall socket. If you dont, its
> > not really grounded. I dont suppose any one has ever done this, but some people
> > might forget. That might be the problem/
> 
> Actually, the outlet is a 3-prong, grounded outlet. I believe it's the
> fact that the sub woofer is connected to a ground that the hum exists
> at all. The problem is likely due to a difference in potential between
> the ground on the sub, and the ground on the receiver.
> 
> However, the two grounds should be the same (one is from the telephone
> ground, the other from the 220 main feed, which is grounded no more than
> about 10 feet from the telephone ground).

This difference is enough to cause quite noticable ground differences. 
 
> I think one of the grounds must not be what it pretends to be ;-)
> 
> Tomorrow, I will try running a grounding line between the two and see
> what kind of sparks I get ;-)

Use thick enough wire to do the connection (check what the regulations
say on this what is safe).

Typical practice used in Finland (and quite much aroudn Europe I think) 
is to connect all grounds entering the house together. This means that 
every house has a central grounding bar, to which all grounding electrodes 
and all grounds connect. This will keep the ground potential difference 
between those different systems minimum. This is ghenerally a very good 
and safe practice. Unfortunately even this practice does not always 
guarantee noise-free operation (there can still be enough ground
potential difference to cause noise problem). The ground potential 
differences can be generated withint the system by the magnetic 
fields and the leakage current going to ground wires.

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