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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.
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.
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).
TO ELIMINATE HUM IF THE ABOVE HAS FAILED:
1. Disconnect the power from all outboard devices and
tape machines except for the Smashup, the mixer and
control room monitor power amp.
2. 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.
3. 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!!