ALLEN & HEATH XONE 02, Service Manual

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8 XONE:02 Service Manual
Earthing
The connection to earth (ground) in an audio system is important for two reasons:
1 . SAFETY - To protect the operator from high voltage electric
shock, and
2. 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 the 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.
•
Deal with ground loops Should you experience hum or buzz caused by ground loops,
check first that each piece of equipment has its own separate path to ground. If so,
operate ground lift switches on connected equipment in accordance with the instruction
manuals. Alternatively disconnect the cable screen at the destination end only. This
breaks the offending loop while still maintaining the signal shielding down the length of
the cable.
•
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 the microphone and main outputs as these provide
further immunity by cancelling out interference that may be picked up on long cable runs.
Refer to the cable drawing for information on how to connect balanced and unbalanced
equipment.
•
Route cables to avoid interference To avoid interference pickup keep audio cables
away from mains power units and cables, thyristor dimmer units or computer equipment.
Where this cannot be avoided, cross the cables at right angles to minimise interference.
•
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.