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From: sjc@angband.UUCP (Steve Correll)
Newsgroups: net.audio
Subject: Re: cables and ground loops
Message-ID: <69@angband.UUCP>
Date: Fri, 26-Jul-85 03:33:29 EDT
Article-I.D.: angband.69
Posted: Fri Jul 26 03:33:29 1985
Date-Received: Sun, 28-Jul-85 07:50:55 EDT
References: <379@ucdavis.UUCP>
Distribution: net
Organization: S-1 Project, LLNL
Lines: 22

> My reason for asking is that I have a Hafler 200 amp with what I *believe*
> to be a ground loop problem.  The amp is completely quiet as long as only
> one input channel is connected to a source, but starts to hum slightly
> as soon as both are connected to the same source.  This seems to happen
> regardless of the source (or cables) used.

This does sound like a classic ground-loop problem. If you're willing to
sacrifice one cable to try to fix it, cut off the connector from one end
of the cable, then solder it back--but connect only the center lead, not
the concentric outer shield.

(It's often reasonable to disconnect one end of the shield of an
ordinary unbalanced two conductor audio cable--that is, a cable which
has an inner signal wire plus an outer, concentric shield. Since we
normally connect two audio cables--one for the left channel and the
other for the right--between each pair of components, we are actually
providing a superfluous ground. My old AR turntable is designed this way;
only one cable has its shield connected to the phono plug at the preamp
end, but both have their shields connected to the turntable's ground.)
-- 
                                                           --Steve Correll
sjc@s1-b.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc