From: John Larkin
Subject: Re: Ground loops?
Date: Sun, 15 Sep 2002 11:49:24 -0700
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On Sun, 15 Sep 2002 14:18:36 GMT, James Meyer
>On Sat, 14 Sep 2002 20:39:35 -0700, John Larkin wrote:
>>You haven't said exactly what you're trying to do, so this suggestion
>>might be tweaked in unusual circumstances. But the conventional wisdom
>>of star grounding, and isolating analog and digital grounds, is just a
>>recipe for trouble in most cases. All it does is ensure that various
>>parts of the system have grounds that are all over the place
>>electrically at high frequencies, and flailing around relative to the
>>enclosure, and who wants that?
> Star grounds work quite nicely thankyouverymuch, *if* they are well and
>truly implemented as star grounds.
> What usually happens is that a star grounded system starts out well
>enough but as the design progresses so many exceptions and patches get thrown in
>that by the time the design is "finished" it bears little resemblance to the
>nice clean original star.
the real problem with star grounding is that the ground runs are
inherently inductive. That's not a problem with tube audio, but
digital circuits that drive offboard loads kick out big fast current
spikes, and the 'star ground' conductors have enough inductance and
just plain distance to make them miserable devices for keeping
everything equipotential. So every board becomes its own resonant
stub, with all sorts of fun consequences.
And, as you point out, board interconnects mess up the purity of the
star, and multiboard systems tend to have lots of interconnects and