Allen&Heath PA20-CP User Manual

PA-CP Series

Powered Mixer

USER GUIDE

Publication AP4956

Limited One Year Warranty

This product is warranted to be free from defects in materials or workmanship for period of
one year from the date of purchase by the original owner.

To ensure a high level of performance and reliability for which this equipment has been
designed and manufactured, read this User Guide before operating.

In the event of a failure, notify and return the defective unit to ALLEN & HEATH Limited or
its authorised agent as soon as possible for repair under warranty subject to the following
conditions

Conditions Of Warranty

1. The equipment has been installed and operated in accordance with the instructions in
this User Guide.

2. The equipment has not been subject to misuse either intended or accidental, neglect,
or alteration other than as described in the User Guide or Service Manual, or approved
by ALLEN & HEATH.

3. Any necessary adjustment, alteration or repair has been carried out by ALLEN &
HEATH or its authorised agent.

4. This warranty does not cover fader wear and tear.

5. The defective unit is to be returned carriage prepaid to ALLEN & HEATH or its
authorised agent with proof of purchase.

6. Units returned should be packed to avoid transit damage.

In certain territories the terms may vary. Check with your ALLEN & HEATH agent for any
additional warranty which may apply.

This product complies with the European Electromagnetic
Compatibility directives 89/336/EEC & 92/31/EEC and the
European Low Voltage Directives 73/23/EEC & 93/68/EEC.

This product has been tested to EN55103 Parts 1 & 2 1996 for use in
Environments E1, E2, E3, and E4 to demonstrate compliance with the
protection requirements in the European EMC directive 89/336/EEC. During
some tests the specified performance figures of the product were affected. This
is considered permissible and the product has been passed as acceptable for
its intended use.

Allen & Heath has a strict policy of ensuring all products are tested to the latest
safety and EMC standards. Customers requiring more information about EMC
and safety issues can contact Allen & Heath.

NOTE: Any changes or modifications to the console not approved by Allen &
Heath could void the compliance of the console and therefore the users
authority to operate it.

PA-CP Series User Guide AP4956 Issue 4

Copyright © 2005 Allen & Heath Limited. All rights reserved

Whilst we believe the information in this guide to be reliable we do not assume
responsibility for inaccuracies. We also reserve the right to make changes in
the interest of further product development.

Allen & Heath Limited
Kernick Industrial Estate, Penryn, Cornwall, TR10 9LU, UK

http://www.allen-heath.com

2 PA-CP User Guide

Important Safety Instructions – Read First

Read instructions: Retain these safety and operating instructions for future reference. Heed all

warnings printed here and on the console. Follow the operating instructions
printed in this User Guide.

Do not open: There are no user serviceable parts inside. Refer any service work to

competent technical personnel only.

Power sources: Connect the console to mains power only of the type described in this User

Guide and marked on the rear panel. The power source must provide a good
ground connection.

Power cord: Use the power cord with sealed mains plug appropriate for your local mains

supply as provided with the console. If the provided plug does not fit into your
outlet consult your service agent. Route the power cord so that it is not likely to
be walked on, stretched or pinched by items placed upon or against it.

Grounding: Do not defeat the grounding and polarisation means of the power cord plug.

Do not remove or tamper with the ground connection in the power cord.

Ventilation: Do not obstruct the ventilation slots or position the console where the air flow

required for ventilation is impeded. If the console is to be operated in a rack
unit or flightcase ensure that it is constructed to allow adequate ventilation.

Moisture: To reduce the risk of fire or electric shock do not expose the console to rain or

moisture or use it in damp or wet conditions. Do not place containers of liquids
on it which might spill into any openings.

Heat: Do not locate the console in a place subject to excessive heat or direct sunlight

as this could be a fire hazard. Locate the console away from any equipment
which produces heat such as power supplies, power amplifiers and heaters.

Environment: Protect from excessive dirt, dust, heat and vibration when operating and

storing. Avoid tobacco ash, drinks spillage, and smoke, especially that
associated with smoke machines.

Handling: To prevent damage to the controls and cosmetics avoid placing heavy objects

on the control surface, scratching the surface with sharp objects, or rough
handling and vibration. Protect the controls from damage during transit. Use
adequate packing if you need to ship the unit. To avoid injury to yourself or
damage to the equipment take care when lifting, moving or carrying the unit.

Servicing: Switch off the equipment and unplug the power cord immediately if it is

exposed to moisture, spilled liquid, objects fallen into the openings, the power
cord or plug become damaged, during lightening storms, or if smoke, odour or
noise is noticed. Refer servicing to qualified technical personnel only.

Installation: Install the console in accordance with the instructions printed in this User

Guide. Do not connect the output of power amplifiers directly to the console.
Use audio connectors and plugs only for their intended purpose.

Important Mains Plug Wiring Instructions

The console is supplied with a moulded mains plug fitted to the AC mains
power lead. Follow the instructions below if the mains plug has to be replaced.

The wire which is coloured Green/Yellow or Green must be connected to the
terminal in the plug which is marked with the letter E or with the Earth symbol.

This appliance must be earthed.

The wire which is coloured Blue or White must be connected to the terminal in
the plug which is marked with the letter N.

The wire which is coloured Brown or Black must be connected to the terminal
in the plug which is marked with the letter L.

PA-CP User Guide 3

Introduction

Welcome to the Allen & Heath PA Series professional audio mixing system. This user guide describes
the functions of the powered PA-CP models and also provides tips and reference information to help
you get the best from your system. We know you want to get started right away. For this reason we
have kept the guide concise and to the point. We recommend you read it through first. However, if
even that is too much then at least read the QUICK START page before you plug up and go. For
further information on the basic principles of audio system engineering and mixing technique please
refer to one of the specialist publications available from bookshops and audio equipment dealers.
Further training is available using the many seminars and courses available in audio engineering and
related subjects.

We are able to offer further product support through our world-wide network of approved dealers and
service agents. You can also access our Web site on the Internet for full company and product
information. To help us provide the most efficient service please keep a record of your console serial
number, and date and place of purchase to be quoted in any communication regarding this product.

The guide is structured for all levels of user. A brief description
of the controls and technical reference information is available
for experienced engineers who want to get started quickly. For
those of you who want to learn more about the basics of live
sound engineering we have included useful blocks of
information and tips.

Description Control and connector functions are briefly

described together with related technical specifications.

 Information Where you see this symbol you will find an

explanation or background information on a particular topic.

☺ Tips for the user Where you see this symbol you will find

tips and information on using a particular function.

Warnings For your own safety and to prevent damage

to equipment make sure you read and adhere to all warnings.

Model

Serial Number

Place of Purchase

Date of Purchase

4 PA-CP User Guide

Contents

 Information

Phantom power................................................13

Balanced and unbalanced connections .........13

The mic preamp ...............................................14

The HPF (high pass filter) ................................14

The mono channel equaliser ...........................15

Pre and post-fade aux sends...........................16

Effects sends....................................................16

Foldback sends................................................16

The dB fader scale ........................................... 17

The dB explained .............................................17

PFL explained ..................................................17

The stereo channel equaliser ..........................19

Wet and dry effects signals .............................20

Effects processing engines .............................22

AFL explained ..................................................24

Gain structure................................................... 24

Sub bass speakers ..........................................25

The amplifier design philosophy .....................26

Constant power explained ...............................26

Front-of-house and foldback monitors............27

Different amplifier configurations..................... 27

Why the parametric output equaliser .............. 27

TRS jack ...........................................................28

Line level...........................................................28

Impedance balanced outputs ......................... 28

SPDIF explained...............................................30

Main Topics

Important Safety Instructions ............3

Overview............................................ 6

The PA Range....................................7

Key Features......................................7

Panel Layout...................................... 8

Quick Start......................................... 9

Installing the Console......................10

Mains Power and Earthing ..............11

Cable and Connector Information...12

The MONO Channel........................ 13

The Mono Equaliser ........................ 15

The STEREO Channel.....................18

The Stereo Equaliser....................... 19

☺ Tips for the user

Working with different channel sources .......... 13

Setting the channel gain ..................................13

Using the HPF (high pass filter) ...................... 14

Using the channel equaliser ............................15

Using more than one effects unit ....................16

Setting up a foldback monitor mix ..................16

Using channel pan ........................................... 17

Using the channel faders .................................17

Using PFL .........................................................17

Using the stereo channels ...............................18

Mixing two stereo signals into the channel.....18

Sending ST1(3) direct to LR ............................18

Using the stereo channel equaliser.................19

Effects in the monitors .....................................21

Using the FX channel PFL ...............................21

Using the effects ..............................................22

Checking the gain structure ............................24

Using PFL and AFL ..........................................25

Using the AB output equalisers....................... 27

Using line level signals ....................................28

Using balanced or unbalanced connections..28

Working with powered speakers .....................29

Choosing headphones ....................................29

Connecting SPDIF ...........................................30

Patching in speaker processors ......................30

No amplifier output? ........................................31

How to check speaker polarity ........................31

The EFFECTS Channel ................... 20

MIDI and the Effects ........................23

The MASTER Controls.....................24

The AMPLIFIERS .............................26

Amplifier Source Select ................... 27

AB Output Equaliser........................27

The MASTER Connectors ...............28

Specifications .................................. 32

System Block Diagram.................... 33

Fitting the PA12-CP Rack Ears........ 34

Cue Sheet........................................ 35

PA-CP User Guide 5

Overview

PA Series consoles provide all the tools you need to run a small PA system in an easy ‘walk up and

go’ format. You simply plug in your microphone and line sources and connect to the speakers. All the
control and processing you need to run a small PA system is built into the console.

Two powered models are available. The PA12-CP has 8 mono and 2 dual stereo channels. The
PA20-CP has 16 mono and 2 dual stereo channels. Both are portable and include protective side
trims and front carry handles. The PA12-CP can be mounted in a standard 19” rack or plinth by
removing its trims and fitting optional rack ears provided.

The two amplifiers can be configured in several different ways according to your PA requirements. For
example, you may run a stereo house system without monitors, or a mono system with additional
musicians monitor speaker, or you may connect to externally powered house speakers and use the
internal amplifiers for two independent monitor speakers. The additional mono line output can be
used, for example, to feed a sub bass amplifier/speaker system or another listening zone.

The power amplifier is without doubt the most critical device in the audio signal path. It converts a
reservoir of power derived from the mains supply into amplified sound. The PA-CP amplifier is a third
generation design that has been rigorously field tested both for absolute reliability and sound quality. It
uses a solid, no-nonsense 1.6kW linear power supply and bi-polar assisted MOSFET Class AB
amplifier design. The unique Allen & Heath constant power system ensures that all the available power
is converted into useable speaker power so achieving the full 500W per side into 4 ohms or 8 ohms.
Full protection is provided including isolating relays, short circuit and over current protection, output
sensing clip limiter, and twin fan thermal management.

We recognise the importance of accurate equalisation both for creative sound processing and for
dealing with problems such as feedback and room resonance. The channel strip features a powerful 4
band EQ with two mids, one with swept frequency. We have chosen to include 4 band semi­parametric rather than traditional graphic EQ on the amplifier channels. These provide far greater
accuracy and therefore less colouration of the sound. Our ‘EQ Visualiser’ software is available to help
you learn how the parametric controls affect the frequency response.

Years of designing mixers and listening to our customers has resulted in a control surface that presents
a well thought out set of functions including many innovative touches that make the job of mixing a
simple pleasure. Notable features include individual phantom power, space saving dual stereo inputs,
standby and BGM (background music) modes, built-in digital effects processor, lamp connector,
selectable sub filter, recording source selector and even an SPDIF digital output.

The name Allen & Heath is well regarded in the professional audio world. The standards applied to our
top end consoles also apply to the PA Series. High grade circuits and components, 100mm Alps
faders, individual vertical circuit cards with sealed potentiometers nutted to the panel, solid grounding
with internal copper buss and steel chassis construction are just a few of the qualities that put this
powered mixer into a class of its own. Our objective was to provide a truly professional solution for
small system mixing. We hope you enjoy using your PA Series console.

6 PA-CP User Guide

The Range

PA20-CP

16 mono MIC/LINE channels

2 dual stereo LINE channels

PA12-CP

8 mono MIC/LINE channels

2 dual stereo LINE channels

Both Models

LR main output

Mono output summed from LR

4 Auxes – 2 pre-fade foldback, 1 post-fade aux, 1 post-fade effects

External stereo effects input to sum with internal effects

AB amplifiers with slave output and amplifier breakpoint inputs

2-Track input for monitor and BGM replay

2-Track recording with analogue and digital SPDIF outputs

Headphones monitor

Key Features

• Constant power amplifier for 2x 500W into 4 or 8 ohms

• Semi-parametric output EQ for more accurate frequency control

• 4 Band channel EQ with swept high mid and 250Hz low mid

• Built-in stereo digital effects with external summing and MIDI control

• SPDIF digital audio output

• Dual stereo channels for summed or 4 independent inputs

• Standby and post-LR BGM operating modes

• Switchable sub bass filter on mono output

• Individual +48V phantom power switching

• 100mm faders, mutes and inserts throughout

Accessories

Rack Ears

A pair of metal ears to replace the
trims and fix the console into a 19”
rack or custom furniture.

PA EQ Visualiser

Runs on a PC to display how the
parametric output EQ affects the
frequency response

AL4061 Lamp

Plug-in XLR gooseneck lamp to
illuminate the control surface

PA-CP User Guide 7

5

0

-5

20

-5
10

30

10

40

MIC

50

LINE

12kHz

-15

600

350Hz 7k

60Hz

63-5-10

100Hz

+15

1k5

+15-15

+15-15 -15

25

3k

FB1

+6O

O OO

FB2

+6O

O

AUX

+6OO

=

PAN PAN

RL L

LINE

12kHz

-5
10

00

MIC

-5-10

-15

600

350Hz

-15

60Hz

-15+15-15

FB1

FB2

OO

AUX

OO+6OO

OO

0

-5

20

-5

30

0

MIC

50

LINE

-10

254063

100Hz

12kHz

+15

1k5

-15

3k

600

350Hz

7k

-15

+15

250Hz250Hz250Hz

-15

+15 +15

60Hz

FB1

+6 +6OO

FB2

+6 +6OO

AUX

+6 +6OO

=

PAN

R RL

0

-5

20

10

-5

1k5

=

30

100Hz

+15

7k

+15

+15-15+15

+6OO+6

1010

40

50

2563

3k

12kHz

60Hz

-10

0

5

-30

10

OO

9-10
LR

-10

0

-20

5

-30

10

OO

+15

-15

+6

OO OO

+6OO OO

+6

OO OO

=

RL L R

12kHz

60Hz

-10

0

-20-20

5

-30

OO

10

11-12

LR

-10

0

-20

5

-30

OO

10

-15

+15

-15+15-15

+15

+6

+6

OO+6OO

+6

+6

=

REVERB

HALL 1

HALL 2

ROOM 1

ROOM 2

ROOM 3

PLATE 1

PLATE 2

PLATE 3

30

20Hz

30

20Hz

-10

OO

OO +6

OO +6

70

100 200

120Hz

200

parametric output equaliser

70

100

200

120Hz

200

+10-10 -10

0

3

10

EFFECTS

DELAY 1

DELAY 2

CH / RM 1

CH / RM 2

CHORUS

FLANGER

ROTARY

PHASER

500 2k5

1k

1k

2k 10k

500Hz

500

1k

1k

500Hz

2k

+10 +10-10

MIN

7k

2k5

1k5

2k5

1k5

-10 +10

10k

MIN

20k

+10-10

7k

20k

MAX

LIM

SIG

SPK
OFF

TMP

SPK
OFF

SIG

LIM

FB1LFB1

L R+RFB2

MIN

MAX

3

5k

+10-10+10-10+10-10

2k5

5k

10k

7

+6OO

POST-LR
PRE-LR

TO

MAX

+6OO

POST-LR FADER

PK ! PK !

PK !

PK ! PK !

STEREO STEREO STEREO

PK !

8 PA-CP User Guide

Quick Start 

6

1 Ensure your safety First read and understand the Important Safety Instructions printed earlier.
Make sure that all your equipment is set for your local mains supply voltage and correctly grounded to
ensure your safety. Check that the console rear panel ON/OFF switch is in its out position (off). Plug in
the mains power using the power cord supplied with the console. Do not turn anything on until you
have checked your wiring and control settings. Also make sure the ventilation slots on the front and
rear are not obstructed in any way.

2 Set all controls to their starting position Set the AMPLIFIER levels, channel FADERS, GAINS,
FB, AUX and FX sends, MONO OUT and 2TRK to LR level controls minimum (anti-clockwise). Set PAN
and all EQ controls centre. Set all switches up or out. Make sure the 48V switches next to the MIC
inputs are in the up position. Check that the recessed panel switches are up (flush with the panel).
Use a pen or pointed object to operate these. Starting with the controls set in this way prevents any
unexpected surprises when you switch the system on.

3 Configure the system Decide how you wish to use the amplifiers. Set the AMP A and B source
switches for stereo, mono + monitor, or 2x monitor operation. These switches are recessed to avoid
accidental operation once set. A good starting point is the default stereo operation (both switches up).

4 Connect the loudspeakers Check that the loudspeaker cables are correctly connected at the
speaker end. Plug your speakers into the rear panel A and B Speakon™ connectors. Push the plugs
into the sockets and twist them into their locked position. Use 4 ohm or 8 ohm speakers. Do not use
bridged operation. Set the rear panel CONSTANT POWER slide switch to the correct position for the
speakers used.

5 Plug in a music source Plug a CD player or similar test source into the ST3 inputs on the last
stereo channel. Check that the recessed switch below its GAIN control is flush with the panel. This
routes the ST3 input to the stereo channel.

6 Turn the system on Press the ON/OFF switch to apply power to the console. The front panel
blue power LED lights and you should hear the speaker relays click in after one or two seconds. You
may also hear air movement as the internal fans start up. The meters and several other LED indicators
may pulse as the power rails stabilise. This is quite normal.

7 Adjust the levels and route the signal to the outputs Press the stereo channel PFL button.
Adjust the ST3 GAIN control until the main meters read around ‘0’. Release PFL and raise the channel
and LR faders to their ‘0’ positions. Next, gradually raise the AMP A and B LEV trim controls. You
should hear the music in the speakers. With the meters averaging ‘0’ to ‘+6’ adjust the amplifier LEV
trimmers for the loudest volume you expect from the system. That gets the gain structure about right.

8 Experiment with the system Use the music source to experiment with the EQ and internal
effects. Plug a microphone into one of the mono channels. Make sure the channel is muted when you
plug or unplug microphones, or when you switch 48V phantom power on or off. To find out more
about each control continue to read through the rest of this guide. HAPPY MIXING !

Important Note about Hearing : To avoid damage to your

hearing do not operate any sound system at excessively high volume. This
also applies to any close-to-ear monitoring such as headphones and IEM.

!

Continued exposure to high volume sound can cause frequency selective or
wide range hearing loss.

4

PA-CP User Guide 9

Installing the Console

The PA Series is portable and designed for stand alone operation. The smaller PA12-CP model can
also be 19” rack mounted by replacing the trims with the rack ears provided. Either way, ensure
adequate ventilation around the unit and heed all warnings regarding mains power safety and earthing.

1 Carry Handle Metal handle for lifting and carrying the
console. The weight is centrally distributed. Lift the console by
holding the handle securely in the middle. To prevent damage
to the controls, carry it with the control surface away from you.

The console is necessarily heavy due to the high

power amplifiers built in. To avoid injury to yourself or
damage to the equipment always ensure you are correctly
positioned and grip securely when lifting, moving or
transporting the unit.

2 Feet Protective rubber feet are fitted to both the base and
the rear of the console so that it can be positioned for stand
alone operation or on the floor while it is being carried. This
avoids damage to the mounting surface and console parts.

3 Front and Side Trims The front armrest, carry handle and
side trims offer both protection and style to the console. They
can be easily removed for fitting the metal ears provided when
you want to permanently mount the console in a 19” rack or
plinth. This option only applies to the smaller PA12-CP model.
Instructions for fitting the rack ears is provided later in this user
guide. The console can be rack mounted in either of two
positions as described below.

4 Rack Position 1 Shows the ears fitted for top of rack
mounting. The controls are angled upwards above the rack for
easier access during operation. This position may also be
preferred when the console is mounted in a desk or other
furniture. 10U rack space is required. Allow additional space
for access to the rear panel connectors.

5 Rack Position 2 Shows the ears fitted for front of rack
mounting. The controls are flush with the rack and connectors
angled slightly back. 11U rack space is required. This allows
space for cables to be routed into the rack, and for the console
lamp to be accessed.

6 Ventilation and Cooling The console uses a twin fan
thermal management system to control the operating
temperature of the built-in 1kW power amplifiers. Air is drawn
in from the front and expelled from the rear. The fans run at
low speed when cool, medium speed on reaching 35 degrees
C, and fast speed at 50 degrees C. The unit shuts down safely
in thermal protect mode in the unlikely event that excessive
temperature is reached.

Do not obstruct the front or rear ventilation slots or

position the console where air flow required for ventilation
is impeded. The console must not be operated in any carry
or flight case that obstructs these slots. Ensure adequate
air flow when rack or plinth mounting the console.

7 Console Lamp Plug in a 4-pin XLR 12V gooseneck lamp
designed for this purpose. The right angled type is
recommended. A low or high intensity bulb up to 400mA
maximum can be used. Only one lamp may be connected.

10 PA-CP User Guide

Mains Power and Earthing

Q

N

F

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.

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

AVIS: RISQUE DE CHOC ELECTRIQUE - NE PAS OUVRIR.

DO NOT OBSTRUCT VENTILATION OPENINGS.
NO USER SERVICEABLE PARTS INSIDE.

WARNING: TO REDUCE THE RISK OF ELECTRIC SHOCK
DO NOT EXPOSE THIS APPARATUS TO RAIN OR MOISTURE.
THIS APPARATUS MUST BE EARTHED BY THE POWER CORD.
RISK OF HAZARDOUS ENERGY! MAKE PROPER SPEAKER CON
SEE OPERATING MANUAL BEFORE USING.

CAUTION: FOR CONTINUED PROTECTION AGAINST RISK OF FIRE
ATTENTION: REMPLACER LE FUSIBLE AVEC UN DES MEMES CARACTERISTI

FUSE

100-240V T10A L

CONSTANT POWER SWITCH

8 OHMS4 OHMS

ON/OFF

0

I

ENGINEERED IN ENGLAND BY ALLEN & HEATH Ltd.

SERIAL NUMBER

MAINS INPUT

V AC ~ 47- 63 Hz

1600W MAX

REPLACE

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.

PA-CP User Guide 11