Alesis ADAT-HD24 FirePort 1394, Reference Manual

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chapter 10 • troubleshooting
ADAT HD24 Reference Manual
93
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 helpful hints that professional studio
installers use to keep those stray hums and buzzes
to a minimum.
¾
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.
¾
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).
¾
TO ELIMINATE HUM IF THE ABOVE HAS
FAILED:
A) Disconnect the power from all outboard
devices and tape machines except for the
ADAT HD24, the 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 mixer 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.
Line Conditioners and Protectors
Although the HD24 is designed to tolerate typical
voltage variations, in today’s world the voltage
coming from the AC line may contain spikes or
transients. These can cause audible noises, and
they can stress your gear and, over time, possibly
cause a failure. There are three main ways to
protect against this, listed in ascending order of
cost and complexity:
• Line spike/surge protectors. Relatively
inexpensive, these are designed to protect
against strong surges and spikes, acting
somewhat like fuses in that they need to be
replaced if they’ve been hit by an extremely
strong spike.
• Line filters. These generally combine
spike/surge protection with filters that
remove some line noise (dimmer hash,
transients from other appliances, etc.). A
good example is the Isobar™ series from
Tripp Lite.
• Uninterruptible power supply (UPS). This is
the most sophisticated option. A UPS
provides power even if the AC power line
fails completely. Intended for computer
applications, a UPS allows you to complete
an orderly shutdown of a computer system in
the event of a power outage. In addition, the
isolation it provides from the power line
minimizes all forms of interference—spikes,
noise, etc.