Manual Samson D-1500 (page 25 of 28) (English)

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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 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 wit

h 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.

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Samson D-1500 Manual

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