TOA 900 SERIES II
Operating Instructions
MIXER PREAMPLIFIER
M-900MK2
THE LIGHTNING FLASH WITH
ARROWHEAD WITHIN A TRIANGLE IS
INTENDED TO TELL THE USER THAT
PARTS INSIDE THE PRODUCT AR E 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.
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.
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.
TOA Corporation
Contents
General description
Features
Nomenclature
Front panel
Rear panel
Input connections
Output connections
Muting and remote volume control connection
Rack mounting
Operation
Volume adjustment
Tone control adjustment
Installation
Servicing
Specifications
Appearance
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— 2 —
General Description
The TOA M-900MK2 Mixer Preamplifier controls and mixes up to eight independent input signals and
delivers up to +20 dBm of output power. Optional plug-in modules are available for use with the M-900MK2 to
provide versatility for a wide choice of operating applications. Edge connectors on the rear of the unit permit
the selection from a wide range of the TOA plug-in modules.
The mixer preamplifier has a balanced and transformer-isolated output for operation with 600 ohms or 150
ohms loads.
Other features include a tone defeat switch, muting functions, remote master volume control and connections
for another mixer preamplifier or mixer power amplifiers A-903MK2, A-906MK2 and A-912MK2.
Features
1. 8-channel mixer preamplifier
2. Wide frequency response : 20~20,000 Hz ± 1 dB
3. Low distortion and noise level
4. Parallel operation of two mixer preamplifiers.
5. Bass and Treble controls
6. Tone defeat switch
7. Remote master volume control
8. A full range of plug-in modules
9. Balanced and transformer-isolated output of 150/600 ohms.
10. Portable or rack mounting type
— 3 —
Nomenclature
< Front Panel >
Power Switch
Applies line power. Two-position push button
switch for on/off modes.
Power Indicator LED
Green LED lights when the power is switched
"ON".
Signal Indicator LED
Green LED lights when more than —30 dB signal
level is fed to the inputs by means of the input
and master volume controls.
Normal Indicator LED
Yellow LED lights when fed to the proper signal
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.
Input Volume Controls
Adjust gain of input #1 ~ #8 respectively.
Bass Control
Modifies bass response. Turn clockwise to boost,
counter-clockwise to attenuate the bass
response. Tone is flat at center.
Treble Control
Modifies treble response. Turn clockwise to
boost, counter-clockwise to attenuate the treble
response. Tone is flat at center.
Tone Switch
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.
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 —
< Rear Panel >
AC Power Cord
Connects to power source.
AC Outlet (Unswitched)
Provides AC power for auxiliary equipment with
power consumption of up to 500W.
Output terminals
Connect to power amplifier.
Module Input Ports
Accepts optional PLUG-IN MODULES.
Module selection is determined by application.
For details, refer to Plug-in Module Instruction
Manual.
AUX Out
Provides connections for a booster amplifier or
tape recorder.
The input impedance of the equipment should be
of more than 10k ohms.
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.
The input impedances of the equipment to be
connected here should be of more than 10k
ohms.
Remote Volume Control Terminals
Connecting a 10k linear taper potentiometer
across these terminals will allow remote control
of preamplifier output.
Mute terminals
Mutes input signals fed to plug-in modules
employing muting function by short-circuiting at
these terminals.
— 5 —
Input Connections
These 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
Connect power amplifier(s) to the output terminal of M-900MK2.
Select 600-ohm or 150-ohm connection, provided at the output terminal to match the input impedance of
amplifier(s).
600-ohm connection
150-ohm connection
AUX Out
For this connection, use RCA phone jack with shielded cable.
Hot
Earth
External equipment such as tape recorder, etc.
Hot
Common
Earth
Hot
Common
Earth
— 6 —
Muting and Remote Volume Control Connection
POTENTIOMETER
10k OHMS
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.
Remove 4 screws securing case.
Amplifier
PF-511 perforated panel (1-unit size)
If two or more units are mounted in an equipment rack, provide
space for ventilation. The perforated panel PF-511 (optional) is
recommended for this purpose.
MB-25B
Fix the brackets with attached 4 screws. The length
of screws should not exceed 12mm (1.2").
— 7 —
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.
with high humidity or dust levels.
with high ambient temperatures.
CAUTION : Do not remove the case or you may encounter an electric shock.
susceptible to vibration.
with poor ventilation.
adjacent to heat-generating equipment.
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.
— 8 —
Specifications
Type
Rated Output
Power Band Width
Frequency Response
Total Hamonic Distortion
Inputs
Input Sensitivity/Impedance
Outputs
Output Regulation (1 kHz)
Signal to Noise Ratio
(Band Pass 20 ~20,000 Hz)
Tone Controls Centered
Tone Contols
Controls
Indicators
Protection
8-channel mixer preamplifier
+4 dBm, +20 dBm (max.)
30 ~20,000 Hz, +20 dBm 0.5% THD
25 ~20,000 Hz, +18 dBm 0.5% THD
20 ~20,000 Hz, ± 1 dB
0.01% 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
Main : Balanced, 150/600 ohms
Aux : Unbalanced, 10k ohms, 0 dBm
Less than 1 .5 dB, no load to full load
Master volume min : 90 dB
Master volume max : 77 dB
Bass: ± 10 dB at 100 Hz, Treble : ± 10 dB at 10 kHz
8 Input gain controls 1 Master gain control
1 Bass tone control 1 Treble control
1 Power ON/OFF switch 1 Tone defeat switch
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 .................. Card-edge connector
Bridging, Aux output ............... RCA phono jack
Connectors
Power Consumption
Temperature Range
Dimensions (W) x (H) x (D)
Weight
Color
Standard Accessories
Other Features
Specifications are subject to change without notice.
Output ..................................... Screw-terminal strip
Mute, Remote VR ................... Screw-terminal strip
AC power cord/plug ................ SJT, 3-prong type
AC outlet ................................. 3-pin grounding type
18W
-10°C~+60°C(12°F~140°F)
420 x 99.1 x 307.5 mm (16.5 x 3.9 x 12.1 in.)
5.3 kg(11.7lb.)
Black
4 Volume control covers (YA-920)
Output disconnected for approx. 5 seconds after switching power on.
— 9 —
Appearance
< Front View >
< Rear View >
< Top View >
< Side View >
— 10 —
TOA Corporation
KOBE, JAPAN
PRINTED IN T AIWA N
133-12-115-50
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