Toa A-901A Instruction Manual

3 Low distortion and noise level
4 Excellent output regulation
5 Bass and treble controls on Input #1 and Program Input
6 Incorporated muting circuit
7 Self-protecting circuitry design
8 A full range of plug-in modules
9 Varied output impedances; 4 and 8 ohms, 25 and 70 volts
10 Clipping indicator
11 Compactness and lightweight
12 Portable or rack-mounting type
The TOA A-901A Mixer Power Amplifier controls and mixes up to
three independent input signals. Producing 10 watts of power, the
A-901A has ideal flexibility for small sound reinforcement systems.
Optional accessory modules are available for use with the A-901 A to
provide versatility for a wide range of operating applications. Edge
connectors on the rear of the unit permit the selection of TOA plug-
in modules : The H-01 series, H-02 series and H-03 series Micro-
phone Preamplifiers, the E-01 Mag. Phono Preamplifier, the X-01
series Auxiliary Preamplifiers for high-level sources, the B-01 series
Bridging Transformers for bridging high-impedance lines, the L-01
series Line Matching Transformers for matching 600-ohm lines, the
I-01 Paging Input for combining with TOA Intercom Systems
EXES-1000, EXES-5000 and EX-16, and the S-01, S-02 and S-03
Tone Signal Generators for generating attention-getting signals and
1kHz sine wave for testing within the total system. Other features
include a muting function. Sources fed to Program Input and
Input 1 are simultaneously muted by short-circuiting at MUTE
TERMINAL on the rear. Accordingly, Input 2 can have priority.
The TOA A-901 A Mixer Power Amplifier has transformer-
isolated 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-901 A can be rack mounted by using the MB-920 Rack-
mounting Bracket Accessory.
TOA Corporation
133-02-735-OA
Printed in Japan
2 Wide frequency response; 20 — 20,000 Hz, ±1dB
1 3-channel mixer power amplifier
TOA NEW 900 SERIES
MIXER POWER AMPLIFIER
Operation Instruction Manual
A-901A
General DescriptionFeatures

Item
1
2
3
4
5
6
Name
POWER ON-OFF
SWITCH
POWER
INDICATOR
(LED)
MAX. OUTPUT
INDICATOR
(LED)
VOLUME
CONTROL for
INPUT #2
VOLUME
CONTROL for
INPUT #1
PROGRAM
INPUT VOLUME
CONTROL
Function/Description
Applies line power. Two-position
pushbutton switch for on-off modes.
Illuminates when power is on.
Green light-emitting diode.
Turns to red when the output
exceeds just above the power rating.
If continuous clipping prevails,
appropriate volume controls should
be adjusted until indicator remains
extinguished.
Adjusts gain of INPUT #2.
Turn clockwise (CW) to increase gain.
Adjusts gain of INPUT #1.
Turn CW to increase gain.
Adjusts gain of PROGRAM INPUT.
Turn CW to increase gain.
Item
1
2
3
4
5
6
7
8
9
10
11
Name
AC POWER
SUPPLY CORD
AC FUSE
(250V, 0.75A)
OUTPUT
TERMINALS
MODULE INPUT
PORT (INPUT #2)
MODULE INPUT
PORT (INPUT #1)
PROGRAM
INPUT
INPUT LIMIT
VOLUME
CONTROL
TREBLE
CONTROL
BASS CONTROL
MUTE
TERMINAL
EARTH
TERMINAL
Function/Description
Connects to power source.
Protects amplifier from excessive
current drain. Replace only with same
type fuse. Refer to qualified service
personnel if fuse blows repeatedly.
Provide connections for speakers.
(See page 2)
Accepts one plug-in input module
accessory. Module selection is
determined by application.
Serves as auxiliary input to accept SCA
tuner, etc.
Preadjusts gain of PROGRAM INPUT
to limit excessive input.
Adjusts treble response on PROGRAM
INPUT and INPUT #1. INPUT #2 is
not influenced by this treble control.
Turn clockwise (CW) to boost and
counterclockwise (CCW) to attenuate
high frequency. Tone is flat at center.
Adjusts bass response on PROGRAM
INPUT and INPUT #1. INPUT #2 is
not influenced by this bass control.
Turn CW to boost and CCW to
attenuate low frequency. Tone is flat
at center.
By short-circuiting at this terminal the
signals fed to PROGRAM INPUT and
INPUT #1 are muted simultaneously.
The signals fed to INPUT #2 are not
muted.
Normally connects to a record
player's ground.
-1-
TOA NEW 900 SERIES
Front Panel Controls and Features
Rear Panel Controls and Features

This unit has two inputs for PLUG-IN MODULES and a program
input.
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.
INPUT MODULES are provided in the following:
H-01 , H-02, H-03, E-01, X-01 , B-01, L-01, S-01, S-02, S-03
* See PLUG-IN MODULES for details.
PROGRAM INPUT CONNECTION
RCA Phono Plug
Hot
Shield
Earth
Input source such as tape
recorder or SCA tuner
MUTE SWITCH CONNECTION
Connect a remote switch for MUTING to the MUTE TERMINAL.
Output transformer taps provide connections for 4-ohm and 8-ohm
speakers, plus 70-volt (490-ohm) and 25-volt (62-ohm) speaker dis-
tribution outlets. Class 2 wiring may be used. Connect to the
terminal of desired impedance and terminal COM (common).
Note: Impedances indicated above imply total speaker
system impedances.
-2-
When all connections are completed, turn power switch on. The
POWER INDICATOR (LED) lights green.
ADJUSTMENT OF VOLUME
Adjust the individual input volume controls to obtain the desired
operating level for respective inputs. If the output level is excessive,
the MAX OUTPUT INDICATOR (LED) will momentarily light, in
which case the gain of corresponding input should be reduced until
this light no longer goes on.
ADJUSTMENT OF TONE QUALITY
The tone quality of INPUT #2 is unadjustable but that of INPUT
#1 and PROGRAM INPUT is adjustable.
Adjust the tone quality using the BASS and TREBLE CONTROLS
(preadjustable) on the rear panel. Each of the controls provides
frequency-response characteristics of boost and attenuation. Normal
or flat response is obtained at center position. Turn CW to boost
response.
Do not block the cover ventilation holes.
The A-901 A should not be placed in areas;
1
2
3
4
5
with poor ventilation.
exposed to direct sunlight.
with high ambient temperature or adjacent to heat-generating
equipment.
with high humidity or dusty levels.
susceptible to vibration.
MUTE
TERMINAL
EARTH
Remote switch
Input Connections
Operation
Output Connections
Installation
CAUTION
Modules should not be inserted or
removed while the A-901 A is turned on.
CAUTION
Do not remove the case, or you may en-
counter an electric shock.

To mount the A-901A in a standard 19-inch equipment rack, use
the MB-920 Rack-mounting Bracket accessory.
Remove 4 screws securing case.
MB-920 (Silver)
(OPTION)
Fix MB-920 with attached 4 screws.
The length of the screws should not exceed 12mm (1/2 inches).
YA-910 (Black)
(OPTION)
Unpacking
Upon receipt of the amplifier shipment, please inspect for any
damage incurred in transit. If damage is found, please notify your
local TOA representative and the transportation company
immediately.
State date, nature of damage, whether any damage was noticed on
the shipping container, prior to unpacking. Please give waybill
number of shipping order.
-3-
Failure
Should amplifier fail, contact your nearest TOA authorized con-
tractor or service center.
TOA NEW 900 SERIES
Rack Mounting
Block Diagram A-901A
Volume Control Cover
Servicing

Type
Output Power
Power Band Width
Frequency Response
Total Harmonic Distortion
Inputs
Input Sensitivity/Impedance
Outputs
(Transformer- isolated)
Output Regulation (1 kHz)
Signal to Noise Ratio
(Band Pass 20 - 20,000 Hz)
Tone Controls Centered
Tone Controls
Controls
Indicators
Protection
Connectors
Power Consumption
Temperature Range
Dimensions in mm (inches)
(high) x (wide) x (deep)
Weight (without input modules)
Color
Standard Accessory
Other Features
3-channel mixer power amplifier
10 watts RMS
50 - 20,000 Hz 2% THD
20- 20,000 Hz, ±1 dB
0.1% at 1 kHz, rated output
Two Input Ports: Each port accepts any input module
except T-01, which cannot be used. (T-01: Line Output Module)
One Program Input
Input Ports #1 & #2: 100 mV/10k ohms
Program Input : 100 mV/50k ohms
Balanced 4,8 ohms, 25 & 70 volts
Less than 2.0 dB, no load to full load
All gain controls max.: 82 dB
Bass; ±10dB at 100 Hz: Treble; ±10dB at 10k Hz
Controls affect only input port #1 and program input.
2 Input gain controls
1 Program gain control
1 Program gain limit control
1 Bass tone control
1 Treble tone control
1 Power ON/OFF switch
1 Power LED 1 Max. output LED
Self-protection, with 1 AC fuse
Inputs #1 and #2
Program input
Output
Mute
AC power cord/plug
Card-edge connector
RCA phono jack
Screw terminal strip
2P socket
SJT, 3-prong type
AC 120 volts, 60 Hz, 30 watts
-10°C to +60°C (12°F to 140°F)
101 (3.98") x 250 (9.84") x 245 (9.65")
Rack-mounting space size "2U" (3.46")
3.9 kg (8.6 Ibs.)
Silver
1 Mute terminal plug
Program input and input port #1 muted simultaneously.
* Specifications are subject to change without notice.
- 4 -
Specifications A-901A

(OPTION)
The TOA PLUG-IN MODULES are suitable for TOA 900 SERIES
MIXER POWER AMPLIFIERS A-901A, A-903A, A-906A, and
A-912A MIXER PREAMPLIFIER M-900A, and POWER AMPLI-
FIERS P-906A, P-912A and P-924. Owing to wide selection of
MODULES, the desired applications will be obtained. The various
types of connectors can also meet the needs of equipment to be
connected. MICROPHONE PREAMPLIFIER H-01 series, H-21 and
H-31 incorporates controls for high-cut, low-cut and gain, H-02
series, H-22, H-32 and H-03 series controls for low-cut and gain.
A gain control is built in MAG. PHONO PREAMPLIFIERS E-01
and E-11 series, AUXILIARY PREAMPLIFIERS X-01 and X-1 1
series and X-21, PAGING INPUT I-01 and LINE OUTPUT T-01
series. T-01 series is an output module with transformer, serving
as a line output for recording, etc..
PAGING INPUT I-01 is specially designed to associate with TOA
INTERCOM SYSTEMS. It accepts paging signals from the intercom
station.
A group of special signal generating modules is also available for
catching-attention before announcement and testing within the total
system. ALL PLUG-IN MODULES have handles on their front for
easy insertion and removal.
Features:
1. Wide dynamic range
2. Low noise and distorition
3. Wide frequency response
4. Built-in remote volume control circuit (available for models
having 20's in its model number such as H-21)
5. Built-in muting circuit to mute incoming signal when MUTE
TERMINAL is grounded, (available for modules having 10's in
its model number such as X-11)
6. Built-in muting circuit to deliver output signal when MUTE
TERMINAL is grounded, (available for modules having 30's in
its model number such as H-31)
7. Built-in signal activated muting function (L-41)
8. Presettable gain control (except for B-01 , B-11 , L-01 and L-11)
9. Microphone modules furnished with tone controls (H-01 , H-02,
H-21 , H-22, H-31, H-32 and H-03)
-5-
(INPUT CONNECTIONS, T-01 OUTPUT CONNECTION)
Plug-in Modules and Accessories
TOA NEW 900 SERIES

Applications
Module
Types
Low Z MIC
with Low & High filters H-01 series
Low Z MIC
with Low & High filters
and remote volume
control facilities
H-21
Low Z MIC
with Low & High filters
and MUTE
H-31
Microphone Preamplitier
Low Z MIC
with Low-cut filter H-02 series
Low Z MIC
with Low-cut filter and remote volume
control facilities
H-22
Low Z MIC
with Low-cut filter
and MUTE
H-32
High Z MIC
with Low-cut filter H-03 series
Mag. Phono
Preamplifier
E-01 series
Auxiliary
Preamplifier
X-01 series
with remote volume
control facilities X-21
Bridging
transformer
B-01 series
Line Matching
Transformer
L-01 series
with Signal Activating
Mute
L-41
Paging Input I-01
Tone Signal
Generator
1 kHz Sine Wave
Buzzer/Yelp
One Tone
Chime
Continuous Chime
S-01 S-02
S-03
Source
Impedance
Input Sensitivity
for Rated Output (100 mV)
Balanced 200 ohms
nominal 1.0 mV adjustable 0.25~25 mV
Unbalanced 50k ohms
nominal 3.2 mV
adjustable 0.8~8.0 mV
Unbalanced
50k ohms
nominal 3.2 mV
adjustable 2.0~5.0 mV
Unbalanced
220k ohms
nominal 100 mV
adjustable 100~3,200 mV
Balanced
10k ohms
125 mV
Balanced 600 ohms
125 mV 125
mV
Min. 15 mV to activate mute function
Balanced 600 ohms
nominal 3.2V
adjustable 3.2~10V
Gain
nominal 40 dB
adjustable 52~32 dB
nominal 30 dB
adjustable 42~22 dB
nominal 34 dB
adjustable 34~26 dB
nominal 0 dB
adjustable 0~—30dB
–1dB –2dB
nominal — 30 dB adjustable — 30~—40 dB
Specifications
Max. Before Clip
into 10k-ohm load
at less than 0.5% THD
(1
kHz)
Output Voltage:
S-01, S-02, S-03
Frequency
Response
±1dB
6.3V(
+
16
dBv)
25~20,000 Hz
6.3V(+16dBv) 20~20,000 Hz 6.3V(+16dBv)
RIAA
Equalized
6.3V(+16dBv) 20~20,000 Hz
20~20,000 Hz 20~20,000 Hz
500~20,000 Hz Low-cut 250 Hz
0.5 V (–6dBv)0.5% THD
1 V peak to peak
1V peak to peak
Noise level
equivalent
input noise
or S/N
Signal
Muting
Level
Remote volume
control range
Use 10k ohms
potentiometer
0~—60
dB
60 dB
-126
dBm
200 ohms
terminated
0~–60dB
60 dB
S/N 70dB
S/N 70dB
S/N 90dB
0~–60
dB
S/N 80 dB S/N 80 dB S/N 80 dB
Controls
pre-
settable
Weight
(max.)
105 gr
(3.71
oz)
1-Low
cut
1-High cut 1-Gain
100 gr
(3.53
oz)
105 gr (3.70 oz) 100 gr
(3.53
oz)
1-Low
cut
1-Gain
95 gr
(3.35
oz)
105 gr
(3.70
oz)
1-Low
cut
1-Gain
60 gr
(2.12
oz)
1-Gain
50 gr
(1.76
oz)
70 gr
(2.47
oz)
1-Gain
65 gr
(2.29
oz)
90 gr
(3.17
oz)
90 gr
(3.17
oz)
1- Sensitivity
95 gr
(3.35
oz)
1-Mute 1-Gain
100 gr
(3.53
oz)
1-Output
55 gr
(1.94
oz)
1-Output
60 gr
(2.12
oz)
1-Output
70 gr
(2.47
oz)
Connector
H-01F H-01M H-01P
H-02F
H-02M
H-02P
H-03P
X-01F X-01P
B-01F B-01P
L-01F L-01P
H-01S
H-21S
H-31S
H-02S
H-22S
H-32S
H-03R E-01R E-01S
X-01R X-01S
X-21S
B-01S
L-01S
L-41S
I-01S
S-01S S-01S S-03S
FORNT PANEL CONTROLS AND FEATURES
Modules with built-in controls are provided in the following five
types.
-6-
GAIN CONTROL SENSITIVITY
CONTROL (L-41S)
NOMINAL POSITION
MARK
This adjusts gain. Turn clockwise (CW) to increase and counterclockwise (CCW)
to reduce gain. Set the gain as low as possible, thereby,
noise can be reduced, and the maximum
permissible input level is raised.
This adjusts sensitivity for muting other
modules having MUTE function. Turn
CW to raise and CCW to lower sensitivity. Setting position should depend on the equipment connected with L-41S.
The left figure shows nominal setting of controls.
LOW-CUT FILTER
CONTROL
330Hz, 6dB/oct
(max. attenuation)
MUTE DE LA Y
CONTROL (I-01S)
HIGH-CUT FILTER
CONTROL
4.2kHz, 6dB/oct
(max. attenuation)
This provides flat characteristics at full
CW position and attenuation in low
frequency by turning CCW. Adjust it to
obtain proper tone quality. With low-cut,
tone becomes clear.
This adjusts MUTE delay time which is
the duration from signal input to its output. Turn CW to shorten and CCW
to lengthen the time.
This provides flat characteristics at full
CW position and attenuation in high
frequency by turning CCW. Adjust it to obtain proper tone quality. With high-
cut, tone becomes soft.
- 7 -
* 0 dBv= 1 volt * Specifications are subject to change without notice.
SPECIFICATIONS IN COMMON
Load impedance :10k-ohms
Mounting : Card-edge connector
Dimensions in mm (inches) : 78(3.07)x35(1.38)x88(3.46)
(H) x (W) x (D)
+ 2
dBm.
XLR-3-13(F)
Type
XLR-3-14(M)
Type
Phone Jack
(P)
RCA Phono
Jack (R) 3P Screw
Terminal(S) 5P Screw
Terminal
(S)
TOA NEW 900 SERIES
Plug-in Modules

- 8-
TOA NEW 900 SERIES
Block Diagrams (Plug-in Modules)

H-31 and H-32 (with mute)
Connections
Remoto switch
Mute
Terminal
Operation
A built-in MUTE circuit of the A-901A mutes signals fed to both
PROGRAM INPUT and INPUT PORT #1 at the same time when
the above remote switch is closed.
Ensure that the INPUT PORT #2 is used when mounting the
H-31 or H-32 on the A-901A. Closing the remote switch causes
signals fed to the H-31 or H-32 to be supplied to the power
amplifier stage.
(While the switch is opened, the signals are attenuated.)
Performance of the MUTE circuit
MUTE Terminal
Opened
Closed
Signals fed to
INPUT PORT #2
with H-31 or H-32
Attenuated(Muted)
Supplied to the
power amp stage
Signals fed to
PROGRAM INPUT
and INPUT PORT #1
Supplied to the
power amp stage
Attenuated (Muted)
L-41 (with signal activated muting facilities)
When this module accepts the input signal, the mute terminal is
grounded automatically without connection of the remote switch
to the MUTE TERMINAL. As a result, signals fed to both PRO-
GRAM INPUT and INPUT PORT #1 are muted.
Ensure that the INPUT PORT #2 is used when mounting the
L-41 on the A-901. When installed into INPUT PORT #1,it does
not work.
H-21, H-22 and X-21 (Remote volume control facilities)
Connections
Potentiometer
10k
Remote
volume
control
Input Connection
Operation
Preset the gain control of module and the input volume control of
the corresponding input so that an appropriate sound level may be
obtained through the remote volume control.
CAUTION
Use the potentiometer of 10K ohms.
Make wiring lest the interference from external noise
should occur.
- 9 -
S-01 (1,000Hz SINE WAVE)
Connections
Remote switch
It is operated by closing the remote
switch.
S-02 (YELP AND BUZZER)
Connections
Yelp signal
Remote switch
Buzzer signal
Each signal is generated by closing cor-
responding remote switch.
Remote switch
S-03 (ONE-TONE CHIME AND CONTINUOUS ONE-TONE
CHIME)
CONNECTIONS
One-tone chime
Remote switch
By closing the remote switch, chime
sounds once.
Continuous one-tone chime
Remote switch
By closing the remote switch, one-tone
chime sounds continuously during the
closure of the switch.
Operation and Connections (Plug-in Modules)

Schematic
A-901A
TOA NEW 900 SERIES