22
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 mar-
ginally 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 hard-
ware store, but are well worth the extra expense.
Three-prong plugs (such as the one used by the S83/S63) should always be used as is; don’t use
adapters to lift the ground (unless you’re using a “star ground network”—see below). If you hear hum or
buzz from a device that uses a two-prong plug (or an external two-prong AC/DC adapter), 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 such as rack ears.
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
that device is the culprit.
We also recommend that you use balanced audio cabling and connectors wherever possible. The
S83/S63 provides electronically balanced inputs for all line channel inputs. The wiring diagram in the
“Connecting The S83/S63” section of this manual shows how 1/4” TRS (Tip/Ring/Sleeve) connectors
should be wired for use with these inputs and outputs.
In addition, you can minimize possible interference by planning your audio, electrical, and computer cable
runs so that they are as far apart from one another as possible and so they don’t run parallel to one
another. If they have to cross, try to ensure that they do so at a 90° angle (that is, perpendicular to one
another). In particular, try to keep audio cabling away from external AC/DC adapters
If you’re using the S83 or S63 in a fixed location such as a recording studio, you may want to invest the
time and money into creating a star ground network. This is by far the best technique for avoiding
grounding problems. It involves using a formidable ground source such as a cold water pipe or a copper
spike driven into the earth. A thick grounding cable is connected to that source and is then brought to a
central distribution point; from there, individual cables are connected to each piece of equipment. This
setup also requires that you lift the ground plug of all three-prong AC connectors, so there is the possibili-
ty of danger if it is done incorrectly. We strongly recommend that you contract with a qualified profes-
sional to carry out this or any kind of electrical work.
Another, less common problem you may encounter is that of oscillation (a ringing tone), which, apart from
being annoying, is potentially dangerous to your speakers. This is generally caused either by poor out-
side wiring or by returning a signal out of phase (most commonly from an outboard signal processor). If
audible oscillation occurs, try isolating each input signal by turning down all other inputs. If one signal
alone is causing the problem, you should be able to eliminate the oscillation by reversing that signal’s
phase (many signal processors have a switch that allows you to do this).
Содержание S63, S83
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