ALLEN & HEATH GR8A Manuel utilisateur

8 Channel Amplifier

GR8A

USER GUIDE

Publication AP4298

2 GR8A USER GUIDE

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.

Any changes or modifications to the equipment not approved by Allen & Heath

could void the compliance of the equipment and therefore the users authority to

operate it.

GR8A User Guide AP4298 Issue 2.

Manufactured in the United Kingdom by

Allen & Heath Limited

Kernick Industrial Estate, Penryn, Cornwall, TR10 9LU, UK

http://www.allen-heath.com

Limited One Year Warranty

This product has been manufactured in the UK by ALLEN & HEATH and is

warranted to be free from defects in materials or workmanship for a 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 or

its authorised agent as soon as possible for repair under warranty subject to the

following conditions

Conditions Of Warranty

The equipment has been installed and operated in accordance with the

instructions in this User Guide

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.

Any necessary adjustment, alteration or repair has been carried out by ALLEN &

HEATH or its authorised agent.

The defective unit is to be returned carriage prepaid to ALLEN & HEATH or its

authorised agent with proof of purchase.

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.

GR8A USER GUIDE 3

WARNING TO THE USER, INSTALLATION ENGINEER

Allen & Heath warns that any unauthorised changes or modifications

to the GR8A unit may invalidate the legal compliance of the unit and

could void the user’s authority to operate the equipment.

DO NOT REMOVE THE MAINS EARTH CONNECTION

To ensure your safety the mains earth is connected to the chassis

through the power lead. Do not remove this connection.

CONTENTS

Warranty............................................................................... 2

Safety Warnings................................................................... 3

Welcome to the Allen & Heath GR8A .................................. 4

General Precautions ............................................................ 4

Specifications....................................................................... 5

Front Panel Controls ............................................................ 6

Rear Panel Controls and Connectors .................................. 7

Installation............................................................................ 9

Operation ........................................................................... 10

Block Diagram.................................................................... 11

SAFETY WARNING!

Mains electricity is dangerous and can kill. Mains

voltage is present within the GR8A.

Do not remove the top cover. There are no user

serviceable parts inside the unit. Refer servicing

to qualified service personnel only.

To avoid the risk of fire, replace the mains fuse

only with the correct value and type as indicated

on the rear panel.

4 GR8A USER GUIDE

Welcome to the Allen & Heath GR8A

The GR8A is one of a range of architectural sound products in the Allen & Heath Contractor Series. It

is an 8 channel audio power amplifier designed to work with multi-output zoning mixers such as the

Allen & Heath GR05, GR1, DR128 and DR66. Modern amplifier technology has enabled the GR8A to

achieve multi-channel high power output in a relatively small case size. Much time and effort has been

invested into making the GR8A an excellent performing, reliable and cost effective solution wherever

multi-channel audio is required. The GR8X transformer rack option is available from Allen & Heath to

enable the amplifier to drive 70V or 100V loudspeaker systems.

This user guide presents a quick reference to the function and application of the GR8A. We

recommend that you read this guide fully before starting. Whilst we believe the information presented 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.

Main Features

•8 Independent audio power amplifiers in a 2U chassis with removable rack ears

•60W per channel into 4 ohms, 40W into 8 ohms

•Outputs bridgeable for 120W into 8 ohms

•Balanced XLR inputs with common mono/stereo source switching in groups of four

•Speaker outputs on Phoenix type removable screw terminal connectors

•3 Colour input signal metering

•Selectable output monitoring on headphones or local speaker

•Full output protection and 3 speed fan cooled temperature management system

•Battery power backup facility

•Remote output ‘standby’ control per channel

Service And Technical Support

Under normal operating conditions the GR8A does not require user maintenance or calibration apart

from occasional vacuuming of the air intake filter should it become ingrained with dust.

To avoid damage to internal components by mishandling and/or misconnection, service

work should be referred only to technically competent personnel.

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 information on our product range,

assistance with your technical queries or simply to chat about audio matters. To help us provide the

most efficient service please keep a record of the serial number, date and place of purchase to be

quoted in any communication regarding this product.

General Precautions

Your GR8A is ruggedly constructed to give many years of reliable operation. However, you will extend

the life of the amplifier and preserve its cosmetics by applying these simple common sense

precautions:

Avoid storing or using the amplifier in conditions of excessive heat or cold, or in positions where it is

likely to be subject to vibration, dust, smoke, dirt or moisture. Do not use any liquids to clean the

control surface of the unit. Use a soft dry brush or dry lint-free cloth. Check the air intake dust filter

regularly and vacuum from the outside to remove dust build up as necessary. Avoid using the amplifier

close to strong sources of electromagnetic radiation such as video monitors, mains and high power

electric cabling.

Do not remove the service cover. There are no user serviceable parts inside. All the controls and

installation settings for the unit are accessible from the outside.

GR8A USER GUIDE 5

Specifications

Connections

Input x8............................................ Balanced XLR pin 2 hot

Speaker x8 ......2 pin Phoenix type pluggable screw terminal

Headphones ........................................ TRS tip left, ring right

Monitor........ Unbalanced TRS tip signal, ring, sleeve ground

Remote standby ........................................ 9 pin D connector

Battery backup.........................4 pin Phoenix type pluggable

AC mains input ....................................................... 3 pin IEC

Input source selection

Independent........................................One input per channel

Common mono.................................Input1 to 1-4 and/or 5-8

Common stereo................Input1/2 to 1/2,3/4 and/or 5/6, 7/8

Input sensitivity for max power ...............................+4dBu

Input impedance................................................> 20k ohms

Input signal meters........................3 colour led per channel

Source ........................................................Post level control

Green..................................................... 140mW into 4 ohms

Amber ......................................................... 10W into 4 ohms

Red.......................................................Approaching clipping

RMS output power per channel

Unbridged............................................ 60 Watts into 4 ohms

Unbridged............................................ 40 Watts into 8 ohms

Bridged .............................................. 120 Watts into 8 ohms

Peak transient power

Unbridged................................................. 130W into 4 ohms

Bridged ..................................................... 250W into 8 ohms

Slew rate................................................................... 10V/uS

Frequency response ...................20Hz to 20kHz +0/-0.5dB

Total Harmonic Distortion

6W into 8 ohms @ 1kHz.............................................. 0.03%

Signal to noise ratio

Relative to 60W into 4 ohms ......................................-100dB

Stand by .................................Separate control per channel

Control.........................Switch common +15V to channel pin

Attenuation ...................................................................-80dB

Inter-channel Crosstalk............relative to 60W into 4 ohms

@ 1kHz......................................................................< -70dB

@ 10kHz....................................................................< -60dB

Protection

Outputs..................................Short circuit, thermal, overload

Power up........................................... 2 second auto standby

Temperature.......... Sensing fan – stop, medium, high speed

Temperature indicator.............. 3 colour – green, amber, red

AC power requirement

Moulded plug to IEC lead supplied (country dependent)

Internally wired for country... 100, 110, 120, 220 or 240V.AC

Operating frequency ............................................... 47-63 Hz

Quiescent................................................................ 50 Watts

Maximum............................................................... 500 Watts

Mains fuse................................................T6.3A 250V 20mm

Battery backup requirement

24V battery x2 ......................................................... 10A max

Dimensions

19” rack mount .......................................482 x 380 x 88 (2U)

Desk mount....................................................440 x 380 x 92

Weight

Unpacked...........................................................12kg (26lbs)

Packed ..................................................................13kg (29lb

6 GR8A USER GUIDE

Front Panel Controls

POWER switch Turns the amplifier on or off. I = on, 0 = off.

TEMP indicator Shows the status of the amplifier temperature

management system:

Green Low temperature Amplifier on, cooling fan stopped

Amber Medium temperature Cooling fan running at slow speed

Red High temperature Cooling fan running at fast speed

SIG indicators Each channel has a 3-colour indicator to monitor the

output signal level:

Green Signal present Turns on at 140mW into a 4 ohm speaker.

Amber Medium level Turns on at 10 watts into a 4 ohm speaker.

Red Signal peak Turns on just before clipping

STANDBY indicators Each channel has a red indicator that lights when

it is in standby mode with its output stage muted. All channels are held in

standby mode for a few seconds when you switch the unit on. This

prevents thumps in the speakers while the power rails stabilise. Selected

channels can be put into standby mode using the rear panel REMOTE

STANDBY connector switching facility.

BRIDGE MODE indicators Each pair of channels has a green indicator

that lights when it is configured for bridged operation using the rear panel

OUTPUT MODE switches.

LEVEL controls Each channel has a rotary control that adjusts its level

from fully off to maximum sensitivity. In bridged mode the odd numbered

channel control sets the overall level and the even numbered control is not

used. Use the level controls to match the amplifiers to the connected

source equipment, set maximum volume allowed, or adjust the balance

between different outputs. Blanking plugs are provided for situations

where tamper-proof level setting is required. Simply set the level, pull off

the knob and push in the blanking plug. The level can be adjusted without

refitting the knob by pulling out the plug and using a small slotted

screwdriver to turn the control shaft.

MONITOR switch 8 Position switch to select one of the 8 amplifier

outputs as the monitor source for headphones or local speaker. This lets

you check the selected amplifier from its speaker terminals attenuated

through a series resistor to match the sensitivity of the headphones.

PHONES socket Plug in headphones to listen to the selected monitor

source. This is a TRS jack socket wired for standard stereo headphones.

The selected channel is monitored in mono.

SENS switch Adjusts the monitor output to match the sensitivity of the

connected headphones. This is an underpanel tamperproof switch to

prevent accidental operation. Use a pen or similar pointed object to

change its setting. The output level is increased when the switch is in its

pressed position.

GR8A USER GUIDE 7

Rear Panel Controls and Connectors

MAINS INPUT The GR8A AC mains voltage setting is factory wired

according to country of order. An IEC power lead with moulded plug

suitable for your mains outlet is supplied with the unit.

Check that the mains voltage marked on the rear panel

matches your local supply.

Read and heed all the warnings printed on the rear panel and

at the start of this user guide.

BATTERY INPUT An emergency back-up supply such as battery or UPS

is a common requirement for public announcement installations. The

GR8A has a 4way Phoenix type pluggable screw terminal input to connect

two 24V DC batteries for back-up power in the event of a loss of mains

supply. Use heavy gauge wire and observe the correct polarity according

to the legend printed above the connector. A mating connector is provided

with the unit.

SIGNAL INPUTS Each channel has a 3-pin female XLR chassis socket

input. These are electronically balanced and wired pin 2 = hot. Input

sensitivity is +4dBu for rated power output. Good quality 2 core screened

signal cable should be used for these inputs to avoid signal degradation or

interference pickup over long cable runs. Use balanced connections

where possible.

INPUT MODE switches Three tamperproof underpanel switches

configure the inputs to allow different combinations of common input

sourcing. Use these when you have one or two sources feeding several

channels. This eliminates the need for custom multi-plug input cables.

8 Independent No common sourcing

4 way mono Input 1 to channels 1–4. 5-8 independent

8 way mono Input 1 to channels 1–8

2 way stereo Input 1 (L), 2 (R) to channels 1/2, 3/4

4 way stereo Input 1 (L), 2 (R) to channels 1/2, 3/4, 5/6, 7/8

MONITOR TRS output with tip = signal, ring and sleeve = ground.

Follows the source selected on the front panel MONITOR switch to feed a

small local loudspeaker or monitoring system as an alternative to the

headphones. The speaker voltage is reduced through a series resistor to

prevent overload. Further attenuation may be needed if this output is to

feed an external amplifier or other line level equipment input.

8 GR8A USER GUIDE

REMOTE STANDBY 9-pin D-type female connector can be wired to

external switches to remotely mute individual channels. Any combination

of channels can be muted at the same time. Putting a channel into

standby mutes its output driver stage. To mute a channel simply switch its

connector pin to the common (+15V) pin. Do not connect the common pin

to any other equipment. The front panel STANDBY indicator lights to warn

that the channel is muted. Use shielded cable for long cable runs.

SIGNAL OUTPUTS These are the amplifier outputs that connect to the

speaker terminals. Each has a 2-way Phoenix type pluggable screw

terminal connector. Mating plugs are provided with the unit. Use suitable

gauge speaker wire, ensure reliable connections and observe the correct

polarity according to the legend printed above the connector. The

following connections are typical.

OUTPUT MODE switches The GR8A amplifier outputs can operate non-

bridged (independently) or be bridged in pairs according to the setting of

the tamperproof underpanel mode switches. Press the switch to select

bridge mode using a pen or similar pointed object. This configures two

amplifiers to work together into one speaker. Use bridge mode when you

need a lot more amplifier power to drive a single speaker.

BRIDGE MODE Use the odd numbered channel input and controls. The

even numbered input is disabled. You should blank off the unused level

controls using the plugs provided. The front panel BRIDGE indicator lights

to show the pair of channels is bridged. If you are using remote standby

switching for the bridged pair make sure you switch them both together.

TRANSFORMER OPTION The high quality GR8X transformer option is

available separately from Allen & Heath to convert the amplifier outputs to

drive 70V or 100V speaker lines. Alternatively, any standard 70V or 100V

line transformer of suitable power rating and quality to match the amplifier

may be used.

To avoid damage to the amplifier make sure you do not

connect a combined speaker impedance of less than 4 ohms in

single mode, or less than 8 ohms in bridge mode.

To avoid damage to the speakers do not drive the amplifier

into clipping or feed it with a previously clipped signal.

Do not use bridge mode when using the amplifier with a 70V

or 100V line transformer.

NORMAL 70V or 100V TRANSFORMER OPTION BRIDGED

GR8A USER GUIDE 9

INSTALLATION

The GR8A can be rack or desk top mounted. It is supplied with rack ears

and desk feet fitted. These may be removed according to the installation

required.

RACK MOUNT The GR8A fits into a 2U space in a standard 19” rack

system. The rack should allow a minimum side to side opening of 445mm

and a depth of at least 420mm to include the connector space required.

Secure the unit into the rack using two M6 bolts on each side. These are

usually provided by the rack supplier and are typically chrome or black

bolts that seat in black plastic cups to prevent scratching the equipment

panel. If space is tight beneath the unit you can remove the plastic feet by

prizing them off. It is advisable to mount the heavier units such as

amplifiers towards the bottom of the rack. This lowers the centre of gravity

for easier handling.

DESK OR SHELF MOUNT Remove the two rack ears. Use a crosspoint

screwdriver to remove the two M4 fixing screws on each side. Make sure

the plastic feet are fitted as these protect the mounting surface from

scratching and prevent the unit sliding.

CABLE ROUTING It is well known that the majority of hum, noise and

routing problems are caused by poor connections and cables. Use high

quality cable and connectors and check for reliable soldering and

assembly. Use balanced connections and screened cables for the inputs.

If you have problems with ground loops lift the screen connection at one

end of the input cables or operate the source equipment ground lift

switches. Use adequately rated speaker wire for the outputs. Input cables

may be run together but outputs should be separated to avoid interaction

between the amplifiers. Route all input and output cables away from

mains, computer and lighting cables.

IMPORTANT WARNINGS !

When positioning the GR8A ensure that the front air intake and the

exhaust vent on the left hand side of the unit are not obstructed or

blocked.

It is normal for the amplifier to run hot when it is working hard. It is

important that air flow around the unit is not restricted. If free air

flow is restricted then additional forced cooling should be provided.

The GR8A is a heavy item. Ensure it is securely fixed where it will

not fall or slip and cause damage or injury.

To avoid damage to the internal assemblies do not fit screws or drill

holes in the sides or underside of the unit. Secure to external

brackets or fittings through the front panel rack mounting holes.

Ensure that the mains voltage setting marked on the rear panel is the

same as your local mains supply.

Do not remove the top cover. There are no user serviceable parts

inside. Refer servicing to qualified service personnel.

To ensure your safety make sure that all the chassis and metalwork

in the rack system is connected to mains earth. Use a continuity

meter to check this. Do not remove any safety earths from

equipment.

10 GR8A USER GUIDE

OPERATION

Switching On

Connect all input and output cables to the unit, ensure it is correctly

installed as described previously and that the input and bridge mode

switches are set as required. Make sure the mains voltage setting is

correct and the mains switch in the ‘0’ off position. Start with all level

controls set minimum. Ensure that all equipment connected to the

amplifier is turned on. Switch the unit on by pressing the mains switch to

its ‘I’ position. The TEMP indicator lights, changing from amber to green

after a few seconds. The fan runs briefly during this time. The STANDBY

indicators illuminate for a few seconds and then go out. This shows that

the outputs are muted while the unit powers up and stabilises.

To avoid loud thumps or damage to your speakers always turn

amplifiers on last and off first.

Setting the Level Controls

It is typical to set the amplifier level controls to maximum and adjust the

volume using the preceding mixer or other equipment controls. This is fine

if the equipment gain structure is correctly set and the preceding

equipment operating level matches the sensitivity of the amplifier. If this is

not the case you can use the amplifier level controls to correct the signal

matching. These controls can also be used to preset the maximum

volume allowed for each output, or to balance the volume between

different outputs. Remove the knobs and fit the blanking plugs provided

with the unit if you wish to lock the controls and make them tamperproof.

Metering

A 3-colour signal meter indicator is provided for each channel to monitor

the output signal level. This is off when there is no signal, green for low

levels, amber for normal levels and red as the signal approaches clipping.

It is very important not to operate the amplifier with the meter

led showing red for more than a brief instant, for example on music

peaks, as this may result in damage to the loudspeaker as the

amplifier clips the music signal. It is also important not to send the

amplifier an already clipped signal as this may also damage the

loudspeaker.

Channel Monitoring

Use headphones or a small speaker to monitor the amplifier output

signals. Select the channel you wish to listen to using the front panel

rotary switch. The signal is sourced from the speaker terminals so that

you can check the signal as it is routed to the speaker.

Fan Cooling

It is normal for the amplifier to run hot when it is working hard. The fan

switches from off to slow to fast depending on internal temperature. The

TEMP indicator lights green, amber or red accordingly.

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