Allen&Heath PA20-CP - Manual (Page 11)

PA-CP User Guide 11
Mains Power and Earthing
Connecting Mains Power
Read the SAFETY INSTRUCTIONS printed at the front of this
user guide and on the rear panel. The power supply is wired for the local voltage required. Check that
the correct mains lead with moulded plug has been supplied with your console, and that the marked
voltage matches your local supply. Ensure that the IEC mains plug is pressed fully into the rear panel
socket before switching on.
To avoid any unexpected audible clicks or thumps
turn connected power amplifiers down or off before
switching the console or any other signal equipment on or
off. The built-in amplifiers include an automatic turn on delay
for this purpose.
Switching On Press the rear panel ON/OFF switch in. The
front panel blue power LED lights. You should hear the
speaker relays switching in after a second or two. This avoids
audible thumps while the circuits stabilise. The front panel SPK
OFF indicators light while the speakers are isolated. You may
also hear air movement as the internal fans start up. The
meters and several other LED indicators may pulse briefly.
This is quite normal.
Switching Off Release the rear panel ON/OFF switch. The
relays switch off instantly to protect the speakers from any
switch off thumps.
Earthing
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 shield
the audio 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 and instrument metal, equipment cases, rack frames, 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.
• Deal with ground loops Should you experience hum or buzz caused by earth loops, check first
that each piece of equipment has its own separate path to earth. If so, operate earth 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. For high impedance instruments use DI (direct inject)
boxes such as those readily available from most music equipment suppliers. The console outputs
are designed to operate at very low impedance to minimise interference problems.
• Use balanced connections for the microphone inputs 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 diagrams for details 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.
Use the correct cable type. 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.
CAUTION
RISK OF ELECTRIC SHOCK
8 OHMS 4 OHMS
CONSTANT POWER SWITCH
DO NOT OPEN
SERIAL NUMBER
FUSE
0
V AC ~ 47- 63 Hz
1600W MAX
MAINS INPUT
CAUTION: FOR CONTINUED PROTECTION AGAINST RISK OF FIRE
ATTENTION: REMPLACER LE FUSIBLE AVEC UN DES MEMES CARACTERISTIQ
SEE OPERATING MANUAL BEFORE USING.
NO USER SERVICEABLE PARTS INSIDE.
DO NOT OBSTRUCT VENTILATION OPENINGS.
RISK OF HAZARDOUS ENERGY! MAKE PROPER SPEAKER CONN
THIS APPARATUS MUST BE EARTHED BY THE POWER CORD.
DO NOT EXPOSE THIS APPARATUS TO RAIN OR MOISTURE.
AVIS: RISQUE DE CHOC ELECTRIQUE - NE PAS OUVRIR.
WARNING: TO REDUCE THE RISK OF ELECTRIC SHOCK
100-240V T10A L
ENGINEERED IN ENGLAND BY ALLEN & HEATH Ltd.
REPLACE F
ON/OFF
I