ALLEN & HEATH GL2800 User Manual

GL2800 User Guide 25
GL2800 Applications and Operating Tips
The following is a collection of brief descriptions, application notes,
hints and tips to help the operator understand some of the technical
terms referred to, and to get the most out of the uniquely capable
GL2800 live sound mixing console. They are written as a concise
reference to spark your imagination to creatively and effectively deal
with the many challenges now faced in modern day mixing.
Gain Structure The term used to describe the gain (level)
matching of the signal through the audio system chain. Each item in
the equipment chain has its own optimum (‘nominal’) operating level
determined by its electrical circuits. If you overload it with a signal that
is too high then its output tries to produce more voltage than its power
rails can provide resulting in harsh sounding distortion as the audio
signal is ‘clipped’. If you work with a signal that is too low then you
are likely to hear the residual hiss of the circuits as the ‘noise floor’ is
amplified along with the signal. The optimum operating level is the
point at which the signal is high enough above the noise floor so that
the hiss is not heard (good ‘signal-to-noise’ ratio, the SNR), yet
provides enough space (‘headroom’) before clipping to allow for the
louder, dynamic musical moments without distortion. ‘Dynamic range’
specifies the maximum range between noise floor and clipping. It is
the sum of the SNR and headroom. The larger the figure the better…
less noise, more headroom, more forgiving to wide ranging signals.
A microphone produces a very tiny signal, for example -50dBu (a few
millivolts). This should be amplified by the channel preamp to the
optimum operating level of the console circuits, around 0dBu
(0.775V), well clear of the noise floor (typically less than -90dBu), and
with good headroom (typically clipping at greater than +20dBu). With
a channel routed at unity gain from preamp input to main output, the
GL2800 boasts a massive 116dB dynamic range. The signal can
pass through many stages which affect its level within the console; the
channel, its EQ, fader, pan, a group mix and its fader, on to the main
LR mix with its master fader, through the matrix, and of course any
inserted equipment. The output XLR provides the professional
standard +4dBu (1.23V) nominal level to the next stage in the audio
chain, typically a speaker processor such as limiter or crossover, or
straight to the amplifier. The amp boosts this signal to tens of volts to
move the speaker cones so producing the audible sound.
To get the best performance from your system, it is important that you
set up the gain structure correctly within the console and also within
and between the connected equipment. Ideally, each circuit should
be set to clip at the same time if the signal became too hot, in other
words each would have similar headroom relative to its nominal
operating level. The resulting dynamic range is the difference
between the highest noise floor and the lowest headroom through the
system. The performance is only as good as the weakest link.
The GL2800 provides comprehensive metering to check every
point within the console signal path. Use the channel meters and
PFL/AFL system to set the gains and mix levels to average around ‘0’
meter reading with usual peaks around ‘+6’. Reduce the gain if the
red ‘+16’ or ‘PK’ indicator lights.
Use the equipment meters to set each item within the system path to
operate at its nominal level. We advise that the speaker processor or
amplifier trims are set so that the console outputs can drive up to their
nominal ‘0’ level. It is a common mistake to set amplifier trims to
maximum sensitivity when this results in the console master faders
being operated at very low positions, with low meter readings, and
reduced dynamic range and therefore audible residual system hiss.
+1
+3
+6
-12
-16
-9
-6
-3
-1
-20
0
+9
-30
-40
-50
-60
-70
-80
-90
+12
+16
+20
SIGNAL-TO-NOISE RATIO
DYNAMIC RANGE
HEADROOM
CLIPPING
NOISE
NORMAL OPERATING RANGE
SIGNAL
!
☺ A search on the Internet
can reveal a host of additional
information on setting correct
gain structure and many other
audio topics and educational
resources.

ALLEN & HEATH GL2800 Specifications

General

Direct Outputs	Yes, on mono channels
Effects	None built-in
Type	Analog
Channels	24, 32, or 40
Stereo Channels	4
EQ	4-band EQ
Phantom Power	+48V globally switchable
Dimensions	Varies by model
Weight	Varies by model
Inputs	Mic/Line inputs on mono channels, stereo line inputs on stereo channels
Outputs	Main L/R, Groups, Matrix, Aux
Faders	100mm
Auxiliary Sends	10 aux sends
Groups	8 groups
Power Supply	Internal power supply with external backup option

Summary

Limited One Year Warranty

Conditions Of Warranty

Important Safety Instructions

Safety and Operation Guidelines

Covers cautions, risks, grounding, water/moisture, ventilation, heat, servicing, power, and cord routing.

General Precautions

Handling, Environment, and Maintenance

Advice on preventing damage, environmental protection, cleaning, lifting, transport, and hearing protection.

Mains Plug Wiring

Instructions for replacing the mains plug, including wire colour codes.

Panel Layouts

The Range

Rear Panel Connectors

Introducing the GL2800

Key Features

Lists the main capabilities and specifications of the GL2800 console.

Installing the Console

Placement and Ventilation

Advice on console placement, ventilation, and avoiding electromagnetic interference.

Connecting Power

Power Supply Connection

Instructions for connecting the console's power supply unit (RPS11).

Backup Power Supply

Information on connecting an optional backup power supply for redundancy.

Grounding

Importance of grounding for safety and audio performance to prevent shock and hum.

Audio Connections

Connector Types

Explains common audio connectors and their wiring for the console.

Audio Connections - Balanced and Unbalanced

The Console Connectors

Channel and Master Connectors

Details on Mono/Stereo MIC/LINE IN, MIC OUT, INSERT, DIRECT OUT, STEREO RETURN, and TB/GEN OUT.

Operating Modes

FOH and Monitor Mode Configurations

Explains FOH mode (groups/LR main) and Monitor mode (auxes main, M engineer's wedge).

The MONO Input Channel

MONO Channel Controls and Functions

The STEREO Input Channel

Stereo Channel Controls and Functions

Explains MIC INPUT, STEREO LINE INPUT, EQ, AUX SENDS, BAL, MUTE, PFL, METER, ROUTING, and FADER.

The STEREO Return Channel

Stereo Return Controls and Functions

Covers ST1, ST2 INPUTS, AUX SENDS, MUTE, PFL, ROUTING, and FADER.

The GROUP / AUX Masters

Group and Aux Master Controls

Details AUX MASTERS, AUX AFL, REV mode, GRP to LR/M, PAN, MUTE, and GROUP AFL/FADER.

Mute, Aux 9-10, and L-R-M Masters

Master Section Controls

Covers AUX 9-10 MASTER, REV mode, AUX MUTE, LR to M, METERS, LR MASTERS, M MASTER, and WEDGE mode.

12x4 MATRIX

Matrix Inputs and Controls

Explains EXT IN, GRP 1-8, L,R,M inputs and LEVEL, MUTE controls for the matrix.

2-TRACK REPLAY and CONSOLE MONITOR

Monitoring Functions

Covers console monitor, headphone sockets, stereo monitoring, and monitor selection.

TALKBACK and SIGNAL GENERATOR

Talkback and Signal Controls

Explains TALKBACK enable, TALK latch mode, and SIGNAL GENERATOR controls.

Applications and Operating Tips

Gain Structure Explained

Detailed explanation of signal gain matching for optimal performance and dynamic range.

Using the Oscillator / Noise Generator

Mixing with Faders or Gain Controls

Using PFL / AFL

Tech Talk - Decibels

Using Inserts

Console Operation Basics

Dual Functionality

FOH vs. Monitor Mode Configurations

Details the key differences in operation and control routing between FOH and Monitor modes.

Applications for the Matrix

Matrix Use Cases

Covers mono recording, stereo recording, remote broadcast, zone feeds, delay fill speakers, and hearing assist.

Recording and Monitor Mixes

IEM Mixes and Recording Setup

How to create IEM mixes with ambience and set up for recording with GL2800.

Aux Send Settings

How to configure aux sends as pre or post fader for different routing needs.

Sub Mixes and Direct Outputs

Mix and Aux-Fed Subs

Methods for driving PA sub-bass speakers with dedicated mixes.

Direct Output Usage

How to use direct outputs for recording or monitor sends.

Stereo Channel and Mute Group Usage

Stereo Channel Flexibility

Details on the unique flexibility of full-feature stereo channels and their configurations.

Mute Group Functionality

How to use mute groups for simultaneous channel muting.

Specifications

Performance Specifications

Detailed electrical performance metrics including input/output levels, noise, and EQ.

Mechanical Specifications

Physical dimensions, weight, and model variations of the GL2800.

Connections

Connection Details and Part Numbers

Summary of input/output connections, specifications, and part numbers for accessories.

System Block Diagram

User Options

Configuring Internal Options

Steps for accessing and configuring internal jumpers for alternative settings.

User Option Settings

Channel and Return Jumper Settings

Details on specific internal jumper settings for Aux pre/post EQ, direct output, and channel aux settings.

Talkback and Output Options

Configuration for Talkback mic +48V and return aux pre/post settings.

Output Balance and Sys-Link Options