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Grounding Techniques
Hum and buzz are the biggest enemies you face when interconnecting
a large number of different pieces of equipment to a central audio mixer.
This is because each piece of equipment may operate at a marginally
different voltage (this difference is called
potential
) and, when two
devices at slightly different potential are physically connected with
audio cabling, the end result can be nasty, extraneous noise (mind you,
connecting two devices at
very
different potential can result in a major
electrical shock!).
However, there are several steps you can take to avoid grounding
problems. First, assuming you have an isolated electrical circuit that
can handle the electrical demands of your mixer and all connected
audio equipment (these needs will usually be modest), you should
always plug your mixer and all connected equipment into the same
circuit. If possible, nothing else but this equipment should be connected
to that circuit. If you can’t do this, at least avoid plugging your mixer and
audio equipment into the same circuit that is already powering things
like heavy machinery, air conditioners, heaters, refrigerators, washing
machines, neon signs or fluorescent light fixtures. One particular culprit
that will almost certainly create problems is the standard light dimmer
(the kind that uses silicon controlled rectifiers). Where low-level lighting
is desired, use incandescent fixtures with autotransformer-type dimmers
(sometimes called
Variacs
) instead—these cost considerably more than
the standard dimmer you’ll find at your local hardware store, but are well
worth the extra expense.
If you hear hum or buzz from a device that uses an external two-prong
AC/DC adapter (such as the MIXPAD), you can try reversing the plug in
the socket. If that doesn’t work, you may need to physically ground that
device’s chassis by connecting a wire (called a
strap
) from it to a
grounded piece of metal. Some pieces of equipment have a screw-type
ground post to which the strap can be connected; if not, you can attach
some kind of metallic binding post to the case itself. If you are using
rack-mounted audio devices and are experiencing hum or buzz, there’s
a simple test to determine the source of the problem: while keeping all
devices powered on and connected with audio cabling, physically
remove each device, one by one, from the rack. If the hum disappears
when a particular device is removed, you’ll know that device is probably
the culprit.