Connecting Mains Power; Earthing - ALLEN & HEATH XONE 62 Service Manual

Connecting Mains Power

USER
AC MAINS IN ~
0
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Earthing

The connection to earth (ground) in an audio system is important for two reasons:
1. SAFETY - To protect the operator from high voltage 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 sound engineer check the continuity of the
safety earth from all points in the system including microphone bodies, turntable chassis,
guitar strings, connector cases, equipment panels 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 the 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.
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 where possible 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.
XONE:62 Service Manual
MONO OUT Read the SAFETY INSTRUCTIONS printed at
the front of this Service Manual. Check that the
BOOTH AUX OUT
correct mains lead with moulded plug has been
L L
supplied with the console. The power supply
accommodates mains voltages within the range
100-240V without changing any fuses or settings.
R R
CLEAN FEED
It is standard practice to turn connected power
SERIAL No:
amplifiers down or off before switching the
FUSE
console on or off. Ensure that the IEC mains
plug is pressed fully into the rear panel socket
before switching on.
A chassis earth terminal is
15