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23
Grounding Techniques
Hum and buzz are the biggest enemies you face when
interconnecting a large number of different pieces of
equipment to one another. This is because each piece
of equipments common reference point (ground)
may operate at a marginally different voltage (this dif-
ference is called potential) and, when two devices at
slightly different potential are physically connected
with audio cabling, the end result can be nasty, extra-
neous 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 electri-
cal demands of all connected audio equipment (these
needs will usually be modest), you should always
plug 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 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 fix-
tures. 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 auto-
transformer-type dimmers (sometimes called Variacs)
instead—these cost considerably more than the stan-
dard dimmer you’ll find at your local hardware store,
but are well worth the extra expense.
Three-prong plugs (such as the one used by the
D1500) should always be used as is; don’t use adapters.
If you are using rack-mounted audio devices such as
the D1500 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, that device is the culprit.
We also recommend that you use balanced audio
cabling and connectors wherever possible. D1500 pro-
vides electronically balanced inputs and outputs. The
diagram on pg. 24 shows how XLR 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 exter-
nal AC/DC adapters.
If your D1500 is 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 possibility of danger if it is done incor-
rectly. We strongly recommend that you contract with
a qualified professional 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 having an out of phase signal (most
commonly from an outboard signal processor). If audi-
ble oscillation occurs, you should be able to eliminate
the problem by reversing that signal’s phase (many sig-
nal processors have a switch that allows you to do this).
Using the D1500 with a Patchbay
If you are using the D1500 with an audio patchbay
(such as S patch or S patch plus), you may find it advan-
tageous to connect its inputs and outputs directly to
a pair of patch points. This way, you can opt to route
signal to the equalizer from any source. For example,
in a recording environment where you are using the
D1500 to “tune” the room, you may typically want to
have the control room outputs routed to the equalizer
inputs and the equalizer outputs routed to the power
amplifier(s) driving the control room speakers. For
maximum convenience and flexibility, we recommend
that you half-normal these connections to the D1500
patchpoints, so that the routing will automatically be
made unless a patch cable is inserted. If a different
signal (such as a bus output or insert) needs to be sub-
stituted, you can then override the half-normalled con-
nection simply by inserting a patch cable.