Alesis MULTIMIX 12R, Справочное руководство

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Operating Instructions
Studio 12R Reference Manual
36
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TO ELIMINATE HUM IF THE ABOVE HAS FAILED:
A) Disconnect the power from all outboard devices and tape
machines except for the mixer and control room monitor
power amp.
B) Plug in each tape machine and outboard effect 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 these basic experiments don’t uncover the source of the problem,
consult your dealer or a 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.
Note that the Studio 12R is grounded through its AC cable. Signal
ground is connected to chassis ground, which in turn may be
grounded again by the rack rails. But since almost all of the inputs
and outputs of the Studio 12R are balanced, the ground does not
have to be made part of the signal path unless you are connecting to
unbalanced equipment. If the Studio 12R is mounted in a metal
rack, the mixer shares a common ground with the other equipment
in the same rack. In some cases (such as a star ground scheme), you
may need to use nonconductive rack rails or rack isolators to avoid
ground loops.
To avoid the possibility of electric shock, never defeat the safety
ground found on other equipment in the system. When in doubt
about proper electrical grounding schemes or the power to your
system, consult a qualified, licensed electrician.
Telescoping shield: In fixed installations using balanced outputs
where the amplifier is more than 20' from the mixer and on a
different AC power panel, it may be advisable to disconnect (or
"float") the shield at the amplifier end. This keeps the ground
potential of the amp rack from being conducted back to the mixer.
Even though the mixer-to-amp connection is balanced, any