MOTM

----- Original Message ----- 
From: GeorgeK <george.kisslak@...>
To: <motm@yahoogroups.com>
Sent: Sunday, February 11, 2001 4:43 PM
Subject: [motm] Ground Loops


Well, I just finished building my first modules, the 900, 120, 420 
and 320, and amazingly everything seems to work (and looks great 
too!)  What a sweet filter the 420 is!  (In just a few more days, my 
girl gets some flowers, and I get some sound sources - my 2nd order's 
in!)

I've run into a little problem, however.  When the 900 power supply 
is installed into a rack with the modules and is powered on, I begin 
to pick up some minor 60hz hum; not much, but enough to ruin the dark 
background - Bummer.  (FYI, the rack is wood frame with metal rails.  
A mixer is in a separate all-metal rack.  Everything is plugged into 
the same power strip.  Patch cords are shielded)  I pick up hum 
regardless of which jack/module I plug into.  I visually checked all 
coax solder joints and ground wires; everything looks ok.  Funny 
thing is that even when I disconnect all of the modules' power cables 
from the 900, I still pick up hum whenever the 900 is on.  There's no 
hum when the 900 is not in the rack, whether connected to and 
powering the modules or not.

Is appears the AC ground is part of the common ground with the 
modules when installed in a rack with metal rails.  This is by 
design, correct?  Is it possible that the mixer being in a separate 
rack is a problem?  If anyone on the list has some insight, that 
would be great.

Cheers,
George