Toa A-706, A-724, A-901A, A-903MK2, A-906MK2 User Manual
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TOA Electronics Amplifier Guide
8
VOL
REMT
OUT
IN/
BRG
OUT
AMP
PRE
IN
AMP
PWR
OUT
AUX
MUTE
MUTE
GND
60W
60Hz
120V
COM
DIRECT
25V
70V
UNSWITCHED AC 120V 60Hz
MAX 500W 4A
AC
PROTECT
POWER
PEAK
NORMAL
SIGNAL
MASTER
OFF
TONE DEFEAT
TREBLE
BASS
INPUT 8
INPUT 7
INPUT 6
INPUT 5
INPUT 4
INPUT 3
INPUT 2
INPUT 1
ON
OFF
LOW CUT
OFFONON
PROGRAM
10
MIC
0
TEL
10
10
AUX
10
MODULE
SIGNAL
POWER
ON
OFF
PEAK
HOT
COM
120V 60Hz
120V 50Hz
UNSWITCHED
150W
MAX 500W
CLASS 2 WIRING
PROGRAM
OUTPUT 120W
COM
OUTLET
4A
BREAKER
COM
70V
25V
OUTPUT 1W
RESET
PUSH
HOT
TEL
COM
10
NC
RESET
MUTE
COM
MOH
600
MIC
COM
UNIT
4A
BREAKER
HOT
PUSH
OUTPUT 1W
SENSE
BASS
10
AUX
PREAMP
10
MOH
OUT
MUTE
TREBLE
POWER
IN
MODULE
PAGE
BGM
COM
HOT
INPUT LEVEL
LOW CUT
-20dBV
OFF
ON
INPUT
DC FUSE
DC FUSE
250V 8A
250V 8A
250V 7A
AC FUSE
S.
LISTED
COMMERCIAL
AUDIO EQUIP.
111J
OU
0dBV
NOR
PO
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ON
OUT
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BRG
OUT
AMP
PRE
IN
AMP
PWR
OUTPUT 1W
BASS
10
AUX
PREAMP
MOH
OUT
MUTE
TREBLE
POWER
IN
MODULE
PAGE
BGM
8
VOL
REMT
MUTE
MUTE
GND
60W
60Hz
120V
COM
DIRECT
25V
70V
UNSWITCHED AC 120V 60Hz
MAX 500W 4A
AC
120V 60Hz
MAX 500W
UNSWITCHED
120V 50Hz
150W
DIRECT
4õ 8
MIC
0
UNSWITCHED AC 120V 60Hz
MAX 500W 4A
70V
25V
õ
COM
120V
AC
60Hz
60W
UNIT
BREAKER
4A
PROGRAM
G COM
OUTPUT 120W
COM
4õ
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RESET
HOT
25V
CLASS 2 WIRING
NORMAL
INPUT 5
SIGNAL
INPUT 4
LOW CUT
ONONOFF
OFF
POWER
PEAK
ON
OFF
BGM
INPUT 3
TONE DEFEAT
MODULE
0 10
MUTE
MODULE
A0B
PAGE
TREBLE
AUX
- +
PREAMP
POWER
OUT
IN
MOH
10
0
10
4A
G
600
MIC
COM
MOH
COM
õ G
INPUT 2
TREBLE
AUX
10100
SENSE
PUSH
RESET
0
10
BASS
NC
HOT
0
- +
MUTE
OUTPUT 1W
0
INPUT 1
BASS
REMT
VOL
MUTE
1
MUTE
2
GND
PROGRAM
0 10
OUTLET
BREAKER
TEL
HOT
G
COM
OUTPUT 1W
COM
70V
8õ
INPUT 6
INPUT 7
INPUT 8
PWR
AMP
IN
PRE
AMP
OUT
BRG
IN/
OUT
SIGNAL
MASTER
PROTECT
AUX
OUT
PWR
AMP
IN
PRE
AMP
OUT
BRG
IN/
OUT
PEAK
POWER
ON
OFF
POWER
IN
BGM
DC FUSE
250V 8A
DIRECT
4õ 8
UNSWITCHED AC 120V 60Hz
MAX 500W 4A
70V
25V
õ
COM
120V
AC
60Hz
60W
DC FUSE
250V 8A
AC FUSE
250V 7A
MUTE
10
0
A0B
BASS
TREBLE
0
- +
- +
OUTPUT 1W
MOH
PREAMP
OUT
MODULE
PAGE
AUX
R
LISTED
COMMERCIAL
AUDIO EQUIP.
111J
REMT
VOL
MUTE
1
MUTE
2
GND
LOW CUT
INPUT LEVEL
ON
OFF
0dBV
-20dBV
INPUT
HOT
COM
Guide
TOA Electronics Amplifier Guide
Table of Contents
Introduction............................................................................................................................................................................1
Chapter 1: Selecting An Amplifier......................................................................................................................2
Sound Sources..........................................................................................................................................2
Speaker Requirements........................................................................................................................2
System Function......................................................................................................................................2
Chapter 2: Amplifier Basics......................................................................................................................................4
Signal Flow..................................................................................................................................................4
Audio Levels...............................................................................................................................................8
Impedance................................................................................................................................................10
Chapter 3: Amplifier/Speaker Matching.....................................................................................................11
Low Impedance Systems................................................................................................................11
High Impedance (70.7/25 Volt) Distributed Line Systems.....................................12
How to Design a High Impedance Distributed System...........................................13
Chapter 4: Wiring..........................................................................................................................................................14
Low Level and Line Level Wiring..............................................................................................14
Twisted Pair Wiring..............................................................................................................15
Shielded and Unshielded Cable.................................................................................15
Balanced and Unbalanced Lines...............................................................................15
Transformer Isolation.........................................................................................................16
Speaker Level Wiring.........................................................................................................................16
Minimizing Line Loss..........................................................................................................16
Troubleshooting Guide...............................................................................................................................................17
Load T roubleshooting......................................................................................................................17
Power Tap to Impedance Conversion Chart....................................................................17
TOA Amplifier Overview............................................................................................................................................18
TOA Amplifier Comparison Chart...............................................................................................................21-22
Appendix A: Wire Size Charts.............................................................................................................................A-1
Appendix B: Power Consumption & Thermal Dissipation...........................................................A-2
TOA Electronics Amplifier Guide
TOA Electronics Amplifier Guide
Welcome to the TOA Amplifier Guide!
TOA has been pro viding complete sound systems sinc e 1934. After our first U.S.sales office was established in 1974, our TA-900 Series mixer/amplifiers quickly gained recognition for their unmatched
combination of flexibility,reliability,and performance. Since that time,T O A has steadily expanded and
improved our line of amplifiers,mixer/amplifiers,and associated electronics. The TOA 900 Series,now
in its 3rd generation of product design,is renowned for its flexible modular architechture ,elegant simplicity of operation,and bulletproof reliability. The new BG-M Series builds further on our tradition by
offering the flexibility of a module port in a package that is remarkably affordable without sacrificing
either performance or reliability. With six distinct series of amplifiers and mixer/amplifiers to choose
from,plus a range of mixers,signal processors,and now network audio,TOA offers the most comprehensive line of audio electronics for systems contractors.
The TOA Amplifier Guide is a sound system design tool aimed at helping system designers,sales staff,
installers and end users select the right amplifiers and accessories for their applications. I t includes a
review of the basic concepts of audio amplification,such as signal flow,levels,and impedance,plus
useful references such as thermal dissipation,power consumption and line loss charts,as well as tips
for troubleshooting (including impedance measurement). Further information on speaker system
design and speaker selection and placement may be found in the TOA Speaker Guide,available for
download at www.toaelectronics.com.
Disclaimer: This design guide does not cover all of the general concepts underlying sound system design
and installation, which would require several hundred pages. This guide is not meant to replace the participation of an experienced consultant or engineer.
References: For more in-depth coverage of sound system design principles,we recommend the following two excellent books:
Sound System Engineering, S econd Edition, Don & Carolyn Davis, 1975, 1987 by Howard Sams & Co.
ISBN:0-672-21857-7
Handbook for Sound Engineers:Third Edition,Glen Ballou,Editor,2001,Butterworth & Heinemann. ISBN:
0-240-80454-6
Acknowledgements
Thanks to Steve Mate,Lucas Marciniak,and Martin Gonzalez in the TOA Product Support Group for
their invaluable support and contributions to this project,and to Geraldine Vargas for designing the
layout. This guide is dedicated to the memory of my late father,whose amp-building projec ts on the
kitchen table gave me a love for the smell of solder,and whose demonstrations of loudspeaker sensitivity gave me a love for the art of sound system design.
David Menasco
Product Application Specialist
TOA Electronics,Inc.
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TOA Electronics Amplifier Guide
Chapter 1: Selecting An Amplifier
Amplifiers are the heart of any sound system. In addition to providing the audio power for a system,
amplifiers may also incorporate the input mixing and control functions vital to a system’s operation
(such an amp is called a mixer/amplifier). Selecting the right amplifier or mixer/amplifier for a job
means choosing a set of features and characteristics suited to meet the customer’s needs. The main
characteristics of an amplifier or mixer/amplifier include:The number and type of input channels,the
number of busses (signal paths) and output channels,and the amount of output power per channel.
Dimensions,weight and other basic parameters may also be important,depending on the installation.
Features needed for a job may include: Auto-muting (e.g.voice-over-music),remote volume control,
transformer-isolated inputs/outputs, phantom power, bass/treble controls, multi-level muting, rack
mounting,equalization,or any of a number of other special purpose features.
When selecting an amplifier,there are three key questions to consider:
1. What sound sources will be used?
2. What speakers will it be driving?
3. How does the client or end user need the system to operate?
Answers to these questions will dictate what characteristics and features are needed. Below is a more
detailed look at each question.
Sound Sources
One of the first questions you will need to answer,at least in general, is what sound sources will be
used in the system. Will the system be used with microphones? A CD player? A telephone exchange?
Due to standardization,many sources can be treated similarly — for example,CD and DVD players,
VCRs and computer sound cards all provide unbalanced line level outputs,usually with a similar output level,and thus may be treated the same in the design phase. But it is still important to know how
many such sources you will have,and what other sources may also be used.
Speaker Requirements
Two more key questions when selecting an amplifier is how much power is needed,and what kind of
load (impedance) the speakers will present — and here,the answers will depend on the type of speakers used. It is usually preferable to select the speakers,or at least the general type of speak ers,before
selecting the amplifier. Please refer to the TOA Speaker Guide for information on selection and placement of speakers. Once the type of speakers has been determined,it will be possible to choose an
amplifier with adequate power and an appropriate output impedance. See Chapter 3
“Amplifier/Speaker Matching”for discussions of impedance,power levels,and 70.7V/25V line operation.
System Function
The paramount rule of sound system design is almost too obvious,and yet it is all too often overlooked: it is important to let the system design be guided by the needs of the client or end user,and
the function they need the system to fill. For example,if they need the mic to automatically mute the
music,you will need a mixer/amplifier that includes this feature. O ften,the user won’t be very
TOA Electronics Amplifier Guide
3
specific until after the system is installed and they try to make it work. The designer’s job includes asking enough questions in the beginning to make sure the design will meet the client’s needs. As a
start, imagine yourself in the place of your client, using the system, and asking questions such as
“where will this go?”and “how will this work?” Experience helps a lot in this process,but installers and
designers of all levels of experience can save time and headaches by asking some basic questions at
the outset.
Visit us at
www.toaelectronics.com
to download the
TOA Speaker Design Guide!
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TOA Electronics Amplifier Guide
Chapter 2: Amplifier Basics
Important Concepts: Signal Flow, Level and Impedance
When designing and installing sound systems,mastery of some key concepts helps a great deal. A
basic understanding of signal flow,levels,and impedance can increase your efficiency on the job,and
dramatically reduce the number of costly call-backs.
Signal Flow: The Audio Chain
Signal Flow refers to the path of the sound from the source (page announcement,CD player,satellite
receiver,etc.) to the listener. This path can be very simple,using just a single source,a power amplifier,and one or more speakers,or it can be complex,having multiple sources,multiple paths,and multiple destinations,with extra processing stages. A typical paging system signal path will begin with
two or three sources — for example,background music,paging audio from the phone system,and a
microphone (see fig.1). These will be fed into a mixer ,which combines the sources into one single line .
The mixer output may be fed into an equaliz er,compressor or other processor,or directly to an amplifier. The amplifier increases the power of the signal and feeds it to the speakers. In most smaller systems, the mixer and amplifier sections are integrated in one unit, which may include a built-in or
optional processing stage,such as an equalizing module for premium spe ak ers.
Figure 1: Basic System for Paging and Background Music
Sources
PBX
Phone System
Microphone
Mixer
Music Source
Mixer/Amplifier
Σ
Processor
(optional)
Speakers
Amplifier
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TOA Electronics Amplifier Guide
Figure 2: Basic System Plus Music-On-Hold Output
More complex systems include all these same stages — sources,mixing ,processing ,amplification,and
speakers — but may add additional signal paths (called busses) so that some sources or listening
areas can be treated differently. A common addition to the typical paging system is the Music On
Hold (MOH) output bus. This bus is fed from the music input,and not affected by speaker processing
modules or by mute functions used for the overhead paging (see fig.2).TOA 900 Series amplifiers can
provide an MOH output using the T-12S module, which provides for both the music input and the
MOH output. This module also works with the 900 Series mute bus to allow for muting of the music
during paging announcements to the main output,while the separate MOH output is not muted and
receives no page announcement. TOA BG and BG-M Series amplifiers include MOH outputs as standard features.
Zone paging and multimedia systems can use additional signal paths to route sounds to different
areas (see figs.3 and 4). Figure 3 shows a typical 3-zone paging system for central mic and/or telephone paging with background music. Simple contac t closures, provided by the phone system or
contractor, are used to activate the zones in any desired combination, simultaneously muting the
background music in each activated zone. TOA BG-M Series amplifiers offer an especially economical
solution for this type of zone paging system. The background music may be from sources local to
each zone or distributed from the head-end via the MOH output.
In multimedia applications, multiple signal paths can be used to route speech and music or movie
sound to different speakers,allowing precise matching of speaker type for the intended application.
Figure 4 shows a multimedia system for a lecture hall,training room, or multi-media-ready meeting
room. This system provides for stereo playback of music sources and stereo sound for video,using a
pair of speakers which may be located flanking a fixed or retractable screen, alongside distributed
mono speech. The resulting system can provide powerful and moving reproduction of music and
movie soundtracks and clear, intelligible speech. An optional subwoofer for the music feed further
enhances the impact.
Sources
PBX
Phone System
Microphone
Mixer
Music Source
Mixer/Amplifier Speakers
Σ
Processor
(optional)
to Phone System
Music on Hold input
Amplifier
Figure 3: Three-Zone Paging System
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TOA Electronics Amplifier Guide
Sources
Phone System
Microphone
Dry Contact
Closures
(one pair
per zone)
PBX
BG-M Series
Mixer/Amplifier
Σ
Microphone
To 'Tel' Input
Music Source
Microphone
Local
Local
Speakers
Zone 1
BG-M Series
Mixer/Amplifier
Σ
Mute
Zone 2
BG-M Series
Mixer/Amplifier
To 'Tel' Input
Music Source
Microphone
To 'Tel' Input
Music Source
Local
Σ
Mute
Zone 3
BG-M Series
Mixer/Amplifier
Σ
Mute
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