Avoiding Ground Loop Noise - Alesis Studio 32 Reference Manual

Avoiding ground loop noise

In today's studio, where it seems every piece of equipment has its own computer
chip inside, 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. While there are methods to
virtually eliminate ground loops and stray radio frequency interference, most of the
professional methods are expensive and involve installing a separate power source
just for the sound system. Alternatively, here are some easy helpful hints that a
professional studio installer might use to keep those stray hums and buzzes to a
minimum.
1 KEEP ALL ELECTRONICS OF THE SOUND SYSTEM ON THE SAME AC
ELECTRICAL CIRCUIT. Most stray hums and buzzes happen as a result of
different parts of the sound system being plugged into outlets of different AC
circuits. If any noise generating devices such as air conditioners, refrigerators,
neon lights, etc., are already plugged into one of these circuits, you then have a
perfect condition for stray buzzes. Since most electronic devices of a sound
system don't require a lot of current (except for power amplifiers), it's usually
safe to run a multi-outlet box or two from a SINGLE wall outlet and plug in all
of the components of your system there.
2 KEEP AUDIO WIRING AS FAR AWAY FROM AC WIRING AS POSSIBLE.
Many hums come from audio cabling being too near AC wiring. If a hum occurs,
try moving the audio wiring around to see if the hum ceases or diminishes. If
it's not possible to separate the audio and AC wiring in some instances, make
sure that the audio wires don't run parallel to any AC wire (they should only
cross at right angles, if possible).
3 TO ELIMINATE HUM IF THE ABOVE HAS FAILED:
A) Disconnect the power from all outboard devices and tape machines except
for the Studio 32 mixer and control room monitor power amp.
B ) Plug in each tape machine and outboard effects device one at a time. If
possible, flip the polarity of the plug of each device (turn it around in the
socket) until the quietest position is found.
C) Make sure that all of the audio cables are in good working order. Cables
with a detached ground wire will cause a very loud hum!!
D) Keep all cables as short as possible, especially in unbalanced circuits.
If the basic experiments don't uncover the source of the problem, consult your dealer
or technician trained in proper studio grounding techniques. In some cases, a "star
grounding" scheme must be used, with the Studio 32 at the center of the star
providing the shield ground on telescoping shields, which do NOT connect to the
chassis ground of other equipment in the system.
Studio 32 Reference Manual
Hooking It Up
27