Archive of the former Yahoo!Groups mailing list: 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