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More About the Theory of Grounding
Careful grounding procedures are essential for proper opera-
tion, not only of the mixer, but of the entire audio system.
Many
grounding
techniques
exist, and certainly there are
several
ways
to
achieve
a satisfactorily
grounded
audio
system. Several books have been written on the subject. For
further
information,
consult
the
following
sources:
THE
AUDIO
CYCLOPEDIA
by
Howard M. Tremaine
(Pub.
Howard W. Sams);
SOUND
SYSTEM
ENGINEERING
by
Don and Carolyn
Davis (Pub Howard W. Sams); GROUND-
ING AND SHIELDING
IN INSTRUMENTATION
by Ralph
Morrison (Pub. John Wiley & Sons).
Ground loops (also called "hum loops"), are often caused by
multiple
paths from equipment grounds to the AC main
ground
(or "earth" ground). Ground
loops tend to induce
hum and allow noise to develop in an audio system. In severe
instances, equipment may begin to oscillated due to ground
loops. This oscillation can cause distortion and even damage
to amplifiers and
loudspeakers.
One way to avoid ground
loops is to make sure that there is just one path to the AC
ground
(earth
ground)
for the entire audio
system.
One
popular method, though not necessarily the best or only one,
is to cut the shield ground of XLR-type connector cables at
the input side of the cable. Another technique is to ground
all shields at one piece of equipment, typically the mixer,
and to cut the shields at the other ends of the cables. (With
unbalanced phone jack cables, the shield must be connected
at both ends.)
|
Connect the mixer to the power mains ONLY AFTER CON-
FIRMING
THAT
THE
VOLTAGE
AND
LINE FREQUEN-
CY ARE CORRECT.
(By ail means, USE
A VOLTMETER
. it can save your equipment and the show.) It is also a
good idea to check for proper polarity in the AC outlet. The
Power switch on the mixer should be Off before connecting
the mixer to the mains. As a further precaution, disconnect
the mixer from the mains while audio cables are being
installed.
|
WARNING
Mixer Placement
In any audio system installation, governmental and insurance underwriters' electrical codes must
be observed. These codes are based on safety, and may vary in different localities; in all cases, local
codes take precedence over any suggestions contained
in this manual. For this reason, Nippon-
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