Operating Instructions
TOA 900 SERIES II
MIXER POWER AMPLIFIER
A-903MK2
A-906MK2
A-912MK2
THE
LIGHTNING
FLASH
WITH
ARROWHEAD WITHIN A TRIANGLE IS
INTENDED TO TELL THE USER THAT
PARTS INSIDE THE PRODUCT ARE A
RISK OF ELECTRIC SHOCK TO
PERSONS.
TO REDUCE THE RISK OF ELECTRICAL
SHOCK, DO NOT REMOVE COVER.
NO USER SERVICEABLE PARTS INSIDE.
REFER SERVICING TO QUALIFIED
SERVICE PERSONNEL.
THE EXCLAMATION POINT WITHIN A
TRIANGLE IS INTENDED TO TELL
THE
USER
THAT
IMPORTANT
OPERATING
AND
SERVICING
INSTRUCTIONS ARE IN THE PAPERS
WITH THE APPLIANCE.
Please follow the instructions in this manual to obtain the optimum results from this unit.
We also recommend that you keep this manual handy for future reference.
TOA Corporation
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General Description
The TOA A-903MK2, A-906MK2 and A-912MK2 Mixer Power Amplifiers control and mix up to eight
independent input signals. The A-903MK2 delivers up to 30 watts of output power, the A-906MK2 60 watts
and A-912MK2 120 watts.
Optional plug-in modules are available for use with these mixer power amplifiers 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 mixer power amplifiers have output terminals to match 4- or 8-ohm speaker systems, or speaker
distribution systems may be connected to 25- or 70-volt terminals, and can be rack mounted by using
optional rack mounting bracket MB-25B. The optional perforated panel PF-511 provides suitable ventilation,
finished in color to match the mixer power amplifiers.
Features
1. 8-channel mixer power amplifier
2. Wide frequency response : 20~20,000 Hz 1 dB
3. Low distortion and noise level
4. Remote master volume control
5. Excellent output regulation
6. Bass and treble controls
7. Bridging input/output
8. Self-protection circuitry design
9. Signal processing input/output
10. Varied output impedances : 4 ohms, 8 ohms, 25 and 70 volts
11. A full range of plug-in modules
12. Portable or rack mounting type
–3–
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Nomenclature
Front Panel
Power Switch
Input Volume Controls
Adjust gain of input #1 ~#8 respectively.
Applies line power. Two-position push button
switch for on/off modes.
Bass Control
Modifies bass response. Turn clockwise to boost,
counter-clockwise to attenuate the bass
response. Tone is flat at center.
Power Indicator LED
Green LED lights when the power is switched
"ON".
Signal Indicator LED
Treble Control
Modifies treble response. Turn clockwise to
boost, counter-clockwise to attenuate the treble
response. Tone is flat at center.
Green LED lights when more than –30 dB signal
level is fed to the inputs by means of the input
and master volume controls.
Tone Switch
Normal Indicator LED
Yellow LED lights when fed to the proper signal
Selects ON/OFF of the BASS and TREBLE
controls. When slided to OFF, BASS and
TREBLE controls are active. When slided to ON,
they become inactive to make tone flat.
level.
Peak Indicator LED
Red LED lights when amplifier approaches
clipping level. If steady lit, the input level control
should be turned down until the LED flashes only
intermittently.
Low-Cut Switch
Cuts off unnecessary low frequency.
Master Volume Control
Adjusts overall gain of the unit.
Protection Indicator LED
Remains lit for about 5 seconds after power
switch is turned ON.
–4–
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Rear Panel
AC Power Cord
Preamp Out
Connects to power source.
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.
AC Outlet (Unswitched)
Provides AC power for auxiliary equipment with
power consumption of up to 500W.
Bridging Input/Output
This terminal is used as a mixing bus. Mixing is
achieved when the similar terminal of another
amplifier is connected to this terminal. The output
level taken from this terminal is independent of
Master Volume Control, Bass and Treble
Controls so that the terminal can also be used as
recording output.
Output terminals
Connect to speakers.
Impedance Select Switch
Selects the desired impedance.
Enables unbalanced output of low impedance
when this switch is set to "DIRECT".
The input impedances of the equipment to be
connected here should be of more than 10k
ohms.
Module Input Ports
Accepts optional PLUG-IN MODULES.
Module selection is determined by application.
For details, refer to Plug-in Module Instruction
Manual.
Remote Volume Control Terminals
Connecting a 10k linear taper potentiometer
across these terminals will allow remote control
of preamplifier output.
AUX Out
Provides connections for a booster amplifier or
tape recorder.
Mute terminals
Mutes input signals fed to plug-in modules
employing muting function by short-circuiting at
these terminals.
The input impedance of the equipment should be
of more than 10k ohms.
Power Amp In
Connect to accessory equipment.
–5–
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Input Connections
There are eight INPUT PORTS for PLUG-IN MODULES.
Select the desired modules for each application. Plug the modules
into the INPUT PORTS.
Slide them between the guide rails and secure with two screws.
CAUTION : Modules should not be inserted or removed while
the amplifier is turned on.
Cover unoccupied INPUT PORTS with blank panels. Secure blank panels with screws.
Output Connections (A-903MK2)
The speaker outputs of the amplifier are 4 ohms, 8 ohms, 25V and 70V.
Connect speakers to any one of these outputs.
Class 2 wiring may be used.
There are two types of output;
4 ohms, 25V and 70V via output (matching) transformer
8-ohm direct output.
The connecting method differs in each case. Refer to the following diagrams.
Note : Impedances indicated below imply total speaker system (load) impedances.
To connect speakers to outputs of : 4 ohms, 25V or 70V (BALANCED OUTPUT)
(A-903MK2)
167-ohm
70V line
21-ohm
25V line
4-ohm
Loosen the screw.
Place the impedance switch in 4-ohm position.
Tighten the screw.
Note : Low-cut switch should be in "CUT" position.
Cut off unnecessary low frequency in TRANS OUTPUT to obtain best acoustic condition. The
900MK2 series amplifiers are characteristically flat even in the low frequency range. Thus, in TRANS
OUTPUT the acoustic effect and frequency-response characteristics may be altered.
–6–
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To connect speakers to 8-ohm output (UNBALANCED DIRECT OUTPUT)
(A-903MK2)
8-ohm
Loosen the screw.
Place the impedance switch in 8-ohm position.
Tighten the screw.
Output Connection (A-906MK2/A-912MK2)
The speaker outputs of the amplifier are 4 ohms, 8 ohms, 25V and 70V.
Connect speakers to any one of these outputs.
Class 2 wiring may be used.
There are two types of output ;
8 ohms, 25V and 70V via output (matching) transformer
•4-ohm direct output.
The connecting method differs in each case. Refer to the following diagrams.
Note : Impedances indicated below imply total speaker system (load) impedances.
To connect speakers to outputs of : 8 ohms, 25V or 70V (BALANCED OUTPUT)
(A-906MK2/A-912MK2)
83-ohm(A-906MK2)/
41-ohm(A-912MK2)
70V line
10.4-ohm(A-906MK2)/
5.2-ohm(A-912MK2)
25V line
8-ohm
Loosen the screw.
Place the impedance switch in 8-ohm position.
Tighten the screw.
Note : Low-cut switch should be in "CUT" position.
Cut off unnecessary low frequency in TRANS OUTPUT to obtain best acoustic condition. The
900MK2 series amplifiers are characteristically flat even in the low frequency range. Thus, in TRANS
OUTPUT the acoustic effect and frequency-response characteristics may be altered.
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To connect speakers to 4-ohm output (UNBALANCED DIRECT OUTPUT)
(A-906MK2/A-912MK2)
4-ohm
Loosen the screw.
Place the impedance switch in 4-ohm position.
After all connections are made, tighten the screw.
Muting and Remote Volume Control Connection
POTENTIOMETER
10k OHMS
MUTE 2
MUTE 1
Remote volume control connection limiting
front panel master volume control range.
Rack Mounting
To mount the amplifier in a standard 19" equipment rack, use the optional MB-25B rack mounting bracket.
MB-25B
Remove 4 screws securing case.
Fix the brackets with attached 4 screws. The length
of screws should not exceed 12mm (1/2").
Amplifier
PF-511 perforated panel (1-unit size)
Use the perforated panel PF-511 to provide space for ventilation,
when two or more units are mounted in an equipment rack.
Contact your local TOA dealer for the perforated panel PF-511.
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Operation
After all connections are made, turn power switch ON, illuminating the Power Indicator LED. The amplifier
comes into operation approximately 5 seconds after the power is turned on.
Volume Adjustment
Obtain desired output level by adjusting the individual input and master volume controls. For normal music
playing or announcement, adjust volume using their controls until the normal LED intermittently lights. Sound
quality is deteriorated when the peak LED remains lit.
Tone Control Adjustment
Set the tone switch to the OFF position. This activates the bass and treble controls. The frequency response
characteristics of each control are flat at center, boost in CW and attenuation in CCW positions. When tone
controls are unnecessary, set the tone switch to ON mode.
Installation
Never block ventilation holes.
The amplifier should never be placed in areas
exposed to direct sunlight.
susceptible to vibration.
with high humidity or dust levels.
with high ambient temperatures.
with poor ventilation.
adjacent to heat-generating equipment.
CAUTION : Do not remove the case or you may encounter an electric shock.
Note : When the temperature of heat sink exceeds 105 °C the protection circuit is activated and the output is
disconnected from the circuit. Output is automatically restored when the temperature return to normal
operating parameter.
Servicing
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.
Failure
Should amplifier fail, contact your nearest TOA authorized contractor or service center.
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Specifications
A-903MK2
A-906MK2
A-912MK2
Type
8-channel mixer power amplifier
30W RMS
Output Power
60W RMS
120WRMS
(D)20~20,000Hz, 0.5%THD
(T) 50 ~20,000 Hz, 0.5% THD
Power Band Width
(D) 20 ~20,000 Hz, 1 dB
(T) 20 ~15,000 Hz, 1 dB
(T) 20 ~20,000 Hz, +1 dB, -3 dB
Frequency Response
Total Hamonic Distortion
Inputs
0.02% at 1 kHz, rated output
Eight Input Ports : Each port accepts any input module.
One Bridging Input/Output
Input Port #1 to #8 : 100 mV/10k ohms
Bridging Input/Output: 100 mV/3.3k ohms
Input Sensitivity/Impedance
Preamp OUT/Power Amp IN
1000 mV into 600 ohms/1000 mV, 10k ohms
Main (T): 4 ohms, 25
& 70 volts, balanced
Main (D): 8 ohms,
unbalanced
Main (T) : 8 ohms, 25 & 70 volts, balanced
Main (D) : 4 ohms, unbalanced ,
Aux : 10k ohms, 1V
Outputs (T)=Transformer
(D)=Direct
Aux : 10k ohms, 1V
(D) Less than 0.5 dB, no load to full load
(T) Less than 1.0 dB, no load to full load
Output Regulation (1 kHz)
Signal to Noise Ratio
(Band Pass 20 ~20,000 Hz)
Tone Defeat SW ON
Master volume min : 90 dB
Master volume max : 77 dB
Power amplifier only : 105 dB
Tone Controls
Bass : 10 dB at 100 Hz, Treble :
10 dB at 10 kHz
8 Input gain controls
1 Bass tone control
1 Power ON/OFF switch
1 Master gain control
1 Treble control
1 Tone defeat switch
Controls
1 Low-Cut switch (60 Hz, 6 dB/octave)
Indicators
Protection
1 Power LED, 1 Protect LED, 1 Signal LED, 1 Normal LED, 1 Peak LED
Self-protection, with AC fuse (inside)
Input No.1 to No.8
Bridging, Mixer preamp. output
Power amp. input, Aux output
Output
Mute, Remote VR
AC power cord/plug
AC outlet
Card-edge connector
RCA phono jack
Connectors
Screw-terminal strip
Screw-terminal strip
SJT, 3-prong type
3-pin grounding type
180W
100W
Power Consumption
Temperature Range
60 W
-10 °C ~ +60 "C [12°F~140°F]
420 x 99.1 x 318 mm
[16.5 X3. 9X 14.1 in.]
11.4 kg [25.1 Ib.]
420 x 99.1 x 358 mm
9.6kg [21.2lb.]
Dimensions (W) x (H) x (D)
[16.5 X3. 9X 12.5 in.]
7.8 kg [17.2 Ib.]
Black
Weight
Color
4 Volume control covers (YA-920)
Output disconnected for approx. 5 seconds after switching power on.
Standard Accessories
Other Features
* Specifications are subject to change without notice.
–10–
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Appearance (A-903MK2)
Front View
420
Rear View
Top View
Side View
–11–
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Appearance (A-906MK2/A-912MK2)
Front View
420
Rear View
Top View
Side View
TOA Corporation
PRINTED IN TAIWAN
133-12-114-60
KOBE, JAPAN
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