ALLEN & HEATH XONE:DB4 Guide de l'utilisateur télécharger pdf (Page 44)

Allen & Heath 44 XONE:4D User Guide

The connection to earth (ground) in an audio system is important for

two reasons:

SAFETY - To protect the operator from high voltage electric shock,

and

AUDIO PERFORMANCE - To minimise the effect of earth (ground)

loops which result in audible hum and buzz, and to shield the audio

signals from interference.

For safety it is important that all equipment earths are connected to

mains earth so that exposed metal parts are prevented from carrying

high voltage which can injure or even kill the operator. It is

recommended that a qualified system engineer check the continuity of

the safety earth from all points in the system including microphone

bodies, turntable chassis, equipment cases, and so on.

The same earth is also used to shield audio cables from external

interference such as the hum fields associated with power transformers,

lighting dimmer buzz, and computer radiation. Problems arise when the

signal sees more than one path to mains earth. An ‘earth loop’ (ground

loop) results causing current to flow between the different earth paths.

This condition is usually detected as a mains frequency audible hum or

buzz.

To ensure safe and trouble-free operation we recommend the following:

Have your mains system checked by a qualified electrician. If

the supply earthing is solid to start with you are less likely to experience

problems.

Do not remove the earth connection from the console mains

plug. The console chassis is connected to mains earth through the

power cable to ensure your safety. Audio 0V is connected to the

console chassis internally. If problems are encountered with earth loops

operate the audio ‘ground lift’ switches on connected equipment

accordingly, or disconnect the cable screens at one end, usually at the

destination.

Make sure that turntables are correctly earthed. A chassis earth

terminal is provided on the console rear panel to connect to turntable

earth straps.

Use low impedance sources such as microphones and line level

equipment rated at 200 ohms or less to reduce susceptibility to

interference. The console outputs are designed to operate at very low

impedance to minimise interference problems.

Use balanced connections for microphones and mix output as

these provide further immunity by cancelling out interference that may

be picked up on long cable runs. To connect an unbalanced source to a

balanced console input, link the cold input (XLR pin 3 or jack ring) to 0V

earth (XLR pin 1 or jack sleeve) at the console. To connect a balanced

XLR output to unbalanced equipment, link the cold output to 0V earth

at the console.

Use good quality cables and connectors and check for correct

wiring and reliable solder joints. Allow sufficient cable loop to prevent

damage through stretching.

If you are not sure ... Contact your service agent or local Allen &

Heath dealer for advice.

EARTHING

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ALLEN & HEATH XONE:DB4 Guide de l'utilisateur Page 44

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