MOTM

Heeeey, look at the big brain on Larry!  But seriously, that was a wealth of
information-- thanks!!  I especially loved the electrocuted cow and multiple
earth bit.

So here's a question.  In my studio, I have my computer and audio equipment
all powered from a pair of power strips plugged into the same UPC, which is
plugged into a 3 prong outlet.  (Er, except for the cable modem box, which
is powered from another outlet and has the network wire plugged into the
computer.)  With everything off (except a Waldorf Pulse and possibly the
computer itself-- I forget), every once in a while I hear an intermitten
60hz hum coming from one of the speakers (a powered Mackie).  Its most
likely something like some electrical appliance in the house kicking in, but
I don't know what.  I would have imagined that the UPC would prevent this by
cleaning up the power, but that would appear to not be the case.  Any ideas
what might be happening?  The sound is so quiet I don't even notice it when
things are on and running; its not a problem, so I've never bothered to
investigate.  I'm just curious.  :)

--PBr

-----Original Message-----
From: J. Larry Hendry [mailto:jlarryh@...]
Sent: Tuesday, February 13, 2001 6:00 PM
To: motm@yahoogroups.com
Subject: [motm] Ground Loops - ANSWERS


George, and others,
What used to happen in some older gear and gear with polarized plugs but no
ground is that the neutral sometimes got case connected or otherwise signal
connected by the manufacturer or some other person thinking this was a good
idea.  Non-isolated neutrals are one of the biggest causes of what is called
ground hum or ground loop.  Here is what happens: