Toa A-903A, A-906A, A-912A Operating Instructions Manual
Operating Instruction Manual
TOA NEW 900 SERIES
MIXER POWER AMPLIFIER
Features
General Description
A-903A
A-906A
A-912A
1 6-channel mixer power amplifier
2 Wide frequency response; 20 — 20,000Hz, ±1dB
3 Low distortion and noise level
4 Excellent output regulation
5 Bass and treble controls
6 Bridging input/output
7 Signal processing input/output
8 Self-protect ing circuitry design
9 Varied output impedances; 4 and 8 ohms, 25 and 70 volts
10 A full range of plug-in modules
11 Portable or rack-mounting type
The TOA A-903A, A-906A and A-912A Mixer Power Amplifiers
control and mix up to six independent input signals. The A-903A
deli vers up to 30 wa tts of output power, t he A-906A 60 watts and
the A-912A 120 watts. Optional accessory modules are available for
use with th e A903A, A-906A and A-91 2A to provide versatility for
a wide range of operating applications. Edge connectors on the rear
of the unit permit the selection of the TOA plug-in modules : The
H-01 series, H-02 series and H-03 series Microphone Preamplifiers,
the E-01 and E-11 Mag. Phono Preamplifiers, the X-01 series and
X-11 series Auxiliary Preamplifiers for high-level sources, the B-01
series and B-11 series Bridging Transformers for bridging highimpedance lines, the L-01 series Line Matching Transformers for
matching 600-ohm lines, I-01 Paging Input for combining with TOA
Intercom Systems EXES-1000, EXES-5000 and EX-16, T-01 series
Line Outputs for matching 600-ohm lines and the S-01, S-02 and
S-03 Tone Signal Generators for generating attention-getting signals
and 1 kHz sine wave for testing within the total system. Other
features include a muting function. Sources fed to particular input
module accessories are muted by short-circuiting at MUTE
TERMINALS on the rears. To perform this function, Module E-11,
X-11 series or B-11 series is required.
The TOA A-903A, A-906A and A-912A Mixer Power Amplifiers
have output terminals to match 4- or 8-ohm speaker systems, or
speaker distribution systems may be connected to the 25- or 70-volt
terminals. The A-903A, A-906A and A-912A can be rack mounted
by using Rack-mounting Bracket accessories MB-921 (for A-903A)
or MB-931 (f or A-9 06A and A - 912A). The PF-911 Perforated Panal
(1.73 inches, 1 rack unit) accessory provides suitable ventilation,
finished in color to match the A-903A, A-906A and A -912A.
Toa Electric Co., Ltd.
KOBE, JAPAN
TOA NEW 900 SERIES
Front Panel Controls and Features
A-903A
Item
1
2
3
4
5
6
7
Name
POWER ON-OFF
SWITCH
METER
INPUT VOLUME
CONTROLS
BASS CONTROL
TREBLE CONTROL
TONE SWITCH
MASTER VOLUME
CONTROL
A-906A, A-912A
Function/Description
Applies line power. Two-position push button
switch for on-off modes.
Indicates the output level of the amplifier. At rated
output, it shows 0 VU (at continuous sine-wave
signal input).
When power is turned on, meter illuminates.
Adjust gain of INPUT #1 – #6 respectively.
Adjusts bass response.
Turn cl o c kw i se ( CW ) to boost and counterclockwise
(CCW) to attenuate the bass response. Tone is flat
at center.
Adjusts treble response.
Turn CW to boost and CCW to attenuate the treble
response. Tone is fla t at center.
Selects IN/DEFEAT of the BASS and TREBLE
Cont rols . When this button is depressed (
BASS and TREBLE Controls are active. ( I N )
Whe n pressed again (
make tone flat. (TONE DEFEAT)
Adjusts overall gain of unit.
), they become i nactive to
), the
Block Diagram
— 1 —
Rear Panel Controls and Features
A-903A
Item
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Name
AC POWER
SUPPLY CORD
AC OUTLET
(Unswitched)
AC FUSE
OUTPUT FUSE
OUTPUT TERMINALS
MODULE INPUT
PORTS
LOW-CUT SWITC H
LINK SWITCH
AUX OUT
POWER AMP IN
PREAMP OUT
BRI DG IN G INPUT/
OUTPUT
MUTE TERMINAL
EARTH TERMINAL
A-906A, A-912A
Function/Description
Connects to power source.
Provides AC power fo r auxiliary equipment with
power consumption of up to 500W.
Prevents excessive current flow.
AC FUSE 250V 2A 250V 3A 250V 5A
OUTPUT FUSE 250V 3A 250V 6A 250V 10A
Connect to speakers.
Accept PLUG-IN MODULES which are optionally
available. Module selection is determined by
application.
Cuts off unnecessary low frequency.
Disconnects between preamplifier and power amplifier
when this switch is turned to the "OUT" side, and
other equipment can be connected.
Provides connections for a booster amplifier or a tape
recorder. The input impedances of the equipment
should be of more than 10k ohms.
When using this terminal, set LIN K SWITCH to "OUT"
position.
Connects to a signal processing equipment such as a
limiter, an equalizer etc. The input impedances of the
equipment should be of more than 600 ohms.
In this case, the LI NK SW should be set in the "OUT"
position.
This terminal is used as a mixing bus. Mixina is achieved
when the similar terminal of another amplifier is
connected to this terminal. The output level taken from
this terminal is independent of the MASTER VOLUME
CONTROL, BASS and TREBLE CONTROLS so that the
terminal can also be used as recording output. The
input impedances of the equipment to be connected
here should be of more than 10k ohms.
With modules employing muting function, which are
optionally available, the input signals fed to the
modules are muted by short-circuiting at this terminal.
Normally connects to a record player's ground.
(A-903A) (A-906A) (A-912A)
— 2 —
TOA NEW 90 0 SERIES
Input Connections
This unit has six INPUT PORTS for PLUG-IN MODULES. Select
the desired ones for each application.
Plug the modules into INPUT PORTS, sliding them between the
guide rails, and secure each with two screws.
When not all INPUT PORTS are occupied, cover the vacant
PORTS with blank panels, and secure them with screws.
PLUG-IN MODULES are provided in the following:
Balanced low impedance microphone
premp module (with presettable low-cut
filter, high-cut filter and gain controls)
Balanced low impedance microphone
preamp module (wit h presettable low-cut
filter and gain controls)
Equalized mag. phono preamp. module
(with presettable gain control)
Unbalanced high impedance auxiliay
preamp module (with presettable
gain control)
Balanced 10k
Balanced 600
transformer module
Balanced paging input module
(with presettable gain control and MUTE Delay)
Balanced 600
(with presettable gain cont rol)
Signal tone generator module
(with presettable output level control)
1kHz sine wave
Yelp and buzzer
One-tone chime and co ntinuous one-tone chime
*With H-21 , H-22 and X-21 modules employing volume remote
control functions, connecting a potentiometer (10k ohms) to the
terminal of any of these modules permits the sound volume to be
remotely controlled by means of the connected potentiometer.
* H-31 and H-32 modules incorporate muting functions. If a switch
is connected to MUTE TERMINAL on the rear panel of the ampl i-
fier and closed, these input signals can be passed through. When
the switch is opened, the input signal is muted.
* E-11, X-11, B-11 and L-11 modules incorporate muting functions.
If a switch is connected to MUTE TERMINAL on the rear panel
of the amplifier and closed, these input signals can be muted.
* L-41 incorporates signal activated muting function. Incoming
input signal causes mute terminal to be grounded.
* T-01 is used to feed out mixed signals to external equipment.
*T-01 should be inserted o nly in INPUT POR T #5 or #6.
(See PLUG-IN MODULES for details)
bridging transformer module
line matching
line output module
H-01,
H-02,
X-01,
L-01,
H-21,
H-31
H-22,
H-32
E-01,
E-11
X-11,
X-21
B-01 , B-11
L-11,
L-41
T-01
I-01
S-01
S-02
S-03
Output Connections A-903A
The speaker outputs of the amplifier are 4
70V
(167
Connect speakers to one of these outputs.
Class 2 wiring may be used.
Since these outputs consist of 4
transformer (matching transformer) and direct output of 8
connecting method differs in each case.
See the following diagrams.
Note: Impedances indicated below imply total speaker system
When connecting speakers to any one of the outputs of 4
or 70V
(BALANCED TRANSFORMER OUTPUT);
Note:
In this case, the LOW-CUT SWITCH should be in "CUT" posi-
tion. This amplifier is characteristically flat even in the low
frequency range. Therefore, in TRANS OUTPUT, the acoustic
effect and frequency-response characteristics may be altered.
In TRANS OUTPUT, cut off unnecessary low frequency to
obtain the best acoustic condition.
When connecting speakers to the 8
(UNBALANCED DIRECT OUTPUT);
).
, 25V and 70V via the output
(load) impedances.
output.
8
,
, 25V (21
) and
, the
,25V
— 3 —-
Output Connections P-906A, P-912A
Installation
, 8
The speaker outputs of the amplifier are 4
Connect speakers to one of these outputs.
Class 2 wiring may be used.
Since these outputs consist of 8
transformer (matching transformer) and direct output of 4
connecting method di ffers in each case. See the following diagrams:
Note: Impedances indicated below imply total speaker system
(load) impedances.
When connecting speakers to any one of the outputs of 8
or 70V (BALANCED TRANSFORMER OUTPUT);
(A-906A)
(A-912A)
, 25V and 70V via the output
, 25V and
70V.
, the
, 25V
Do not block cover ventilation holes.
The amplifier should not be placed in areas;
1 with poor ventilation.
2 exposed to direct sunlight.
3 with high ambient temperature or adjacent to heat-generating
equipment.
4 with high humidity or dust levels.
5 susceptible to vibration.
Note:
When the temperature of heat sink exceeds 105°C, the protection circuit is activated and the output is disconnected from the
circuit. The signal automatically begins to be output as the
temperature goes down. In such a case, confirm whether or not
unit is overloaded or operated on an excessive output.
Note:
In this case, the LOW-CUT SWITCH should be in "CUT" position. This amplifier is characteristically flat even in the low
frequency range. Therefore, in TRANS OUTPUT, the acoustic
effect and frequency-response characteristics may be altered.
In TRANS OUTPUT, cut off unnecessary low frequency to
obtain the best acoustic condition.
When connecting speakers to the 4
DIRECT OUTPUT);
(A-906A, A-912A)
output. (UNBALANCED
— 4 —
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