Avoiding Ground Loops - Alesis ADAT-XT20 Reference Manual

Chapter 1: Setting Up
When AC currents are suspect of being highly unstable in VAC and Hz, a
professional power conditioner should be used.
Alesis cannot be responsible for problems caused by using the XT20 or any
associated equipment with improper AC wiring.
A
VOIDING
8
G
ROUND
In today's studio, where it seems every piece of gear has a computer in
it, there are many opportunities for ground loop problems to occur. These
show up as hums, buzzes, or sometimes radio reception and can occur if a
piece of equipment "sees" two or more different paths to ground, as
shown below.
shielded
cable
Device A
path 1
path 2
One path goes from device A to ground via the ground terminal of the
three-conductor AC power cord, but A also sees a path to ground through
the shielded cable and AC ground of device B. Because ground wires
have a small amount of resistance, small amounts of current can flow
through ground and generate a voltage along the cable shield. This
signal may end up getting induced into the hot conductor.
The loop can also act like an antenna into which hum is induced, or can
even pick up radio frequencies. Furthermore, many components in a
circuit connect to ground. If that ground is "dirty" and contains noise, it
might get picked up by the circuit. Ground loops cause the most prob-
lems with high-gain circuits, since massive amplification of even a
couple millivolts of noise can give an audible signal.
Most ground loop problems can be solved by plugging all equipment into
the same grounded AC source. However, it is important to make sure
that the AC source is not overloaded and is properly rated to handle
the gear plugged into it.
For really tough cases, you may need to break the connection that causes
the loop condition. If your circuits are balanced, one way to do this is to
simply break the shield of the shielded audio cable at some point,
usually by disconnecting it from ground at one jack. (The other end
L
OOPS
Device B
To AC power service
ADAT XT20 Reference Manual