Samson TM300 Specifications download pdf (Page 18)

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.

Three-prong plugs (such as the one used by the TM300) 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. 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.

We also recommend that you use balanced audio cabling and connectors wherever possible. The TM300 provides

electronically balanced inputs for all channel line inputs. The wiring diagram in the “Connecting The TM300” section

of this manual (page 10) shows how 1/4" TRS (Tip/Ring/Sleeve) and 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 external AC/DC adapters.

If you’re using the TM300 in a fixed location such as a rehearsal 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 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 incorrectly. 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 outside 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).

ENGLISH

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Samson TM300 Specifications Page 18

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