Allen&Heath WZ14-4-2 - Manual (Page 9)

WZ14:4:2 U SER G UIDE 9
C
ONNECTING
M
AINS
P
OWER
Refer to the SAFETY WARNING on page 3 of the User Guide.
Check the voltage indicated on the rear panel is the same as
the mains supply in your area. Check that the correct mains
lead with moulded plug has been supplied with your console.
Read and understand the warnings and instructions printed on
the rear panel and reproduced here.
It is standard practice to turn connected power amplifiers down
or off before switching the console on or off. Ensure that the
IEC mains plug is pressed fully into the rear panel socket
before switching on.
E
ARTHING
The connection to earth (ground) in an audio system is important for two reasons:
1. SAFETY - To protect the operator from high voltage shock associated with the AC mains
supply feeding the system, and
2. AUDIO PERFORMANCE QUALITY - 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, guitar strings, multicore
cases, equipment panels ...
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:
• 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. It is
useful to carry ground lift cable adapters such as short XLR male to female leads with pin
1 disconnected.
• Avoid running audio cables next to mains, computer or lighting cables, or near
thyristor dimmer and power supply units. If unavoidable, cross these at right angles.
• Use low impedance sources such as microphones 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
console output to an unbalanced destination, link the cold output to 0V earth at the
console.
• Use professional quality cables and connectors and check for correct wiring and
reliable solder joints.
• If you are not sure ... Have your system checked by a competent engineer, or contact
your local Allen & Heath agent for advice.