ALLEN & HEATH WZ20:8:2, Service Manual

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ALLEN & HEATH 2E-8SM
3
TECHNICAL DESCRIPTION
The ALLEN & HEATH MixWizard WZ 20:8:2 is a dedicated 8-track rack mount or desk standing mixer with 8 mono
inputs and 6 stereo inputs. All mono input channels have a 4 band 2-sweep EQ with 6 individual aux sends and Direct
output. The 6 stereo inputs have a 2 band EQ with 2 stereo cue/aux sends and 2 mono aux sends. The 8 tape return inputs
have individual level and pan controls with a stereo cue facility . In addition the
MixWizard WZ 20:8:2 also has extensive
talkback facilities and an internal 1kHz sinewave oscillator for level checking The internal power supply unit is located
in the rotating connector module.
CONSTRUCTION
All metal chassis for 19" rack mount in 10U space. Comprises a 16swg steel front panel housing individual channel
circuit assemblies interconnected by means of soldered copper wire busbars. The connectors are housed in a rotating
connector module for either rack or desk mounted applications. Access to the channel internal assemblies is by removal
of the 18swg folded steel base. Access to the connectors and power supply components is by removal of the rear cover
of the connector module without the need to remove the console base. The channel assemblies may be removed for
servicing.
THE CIRCUIT COMPONENTS
The MixWizard WZ 20:8:2 is manufactured using high performance industry standard linear op-amp and discrete
semiconductor circuit devices. In particular the switches and potentiometers have proven to be durable and problem free.
When operated correctly the normal performance of the unit introduces no noticeable audio signal degradation.
AUDIO INPUTS AND OUTPUTS
All XLR connector inputs and outputs are balanced (differential) with high impedance inputs and low impedance
outputs. To use these with unbalanced equipment the -ve signal should be linked to 0V in the cable or input connector.
All unbalanced connections are line level 3-pole TRS ¼" jack sockets. All outputs are low impedance and thus capable
of driving several high impedance inputs simultaneously. All inputs and outputs are in phase.
THE PFL SYSTEM
The console PFL switches send pre-fade signals to the PFL mix bus. These signals are switched with 4053 CMOS gates
located on the RIGHT circuit board (PCB No: AG2939). The supply for the 4053 is ± 8V DC and is derived locally from
the ±16V. The gates are switched when a PFL switch is selected.
EARTHING THE AUDIO SYSTEM
The console chassis is connected to mains earth via the mains power cable. Console audio 0V is also connected to chassis.
FOR SAFETY REASONS NEVER REMOVE THE EARTH WIRE FROM THE MAINS PLUG.
Multiple earth paths cause earth (ground) loops which may result in audible hum and interference. These may be avoided
by making sure that there is only one path to earth from each piece of equipment, disconnecting audio cable screens at
one end if necessary.
INTERCONNECTIONS
Where possible use balanced connections for the CHANNEL inputs, AUX/CUE SENDs, and both L/R outputs to
minimise noise pick-up. Avoid running audio cables near to mains or lighting cables, thyristor dimmer units or power
supplies etc. These may cause audible hum and buzz. The use of low impedance sources significantly reduces
interference pick-up. Check the cables for correct wiring to avoid problems with phase reversal and unreliable
connection. The
MixWizard WZ 20:8:2 follows the convention for XLR pin 2 and jack tip = signal hot (+).
ALWAYS USE BALANCED CABLES WHEN CONNECTING TO PHANTOM POWERED MICROPHONES.
WHEN USING NON-PHANTOM POWERED OR UNBALANCED MICROPHONES OR UNBALANCED LINE
SOURCES, MAKE SURE THAT THE +48V IS DISABLED TO PREVENT ACCIDENTAL DAMAGE.
INDIVIDUAL CHANNELS CAN HAVE +48V DISABLED, REFER TO THE LINK OPTIONS SECTION IN THE USER
GUIDE OR SERVICE MANUAL.
If ground loops cause problems, connect the cable screen at one end only. Balanced outputs may be connected to
unbalanced inputs and vice versa by linking the signal cold (-) to 0V ground.