Radio Shack MPA-125 User Manual
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MPA-125 100-Watt PA Amplifier
Owner’s Manual
Please read before using this equipment.
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ˆ
Contents
Features .................................................................................................................................. 3
Preparation ............................................................................................................................. 4
Presetting the Controls ...................................................................................................... 4
Presetting Audio Input Devices .................................................................................. 4
Presetting the Amplifier .............................................................................................. 4
Mounting the Amplifier ...................................................................................................... 5
Placing the Speakers ........................................................................................................ 5
Connections ............................................................................................................................ 5
Connecting Input Sources ................................................................................................. 5
Connecting Microphones ........................................................................................... 5
Connecting a Turntable .............................................................................................. 6
Connecting an Auxiliary Sound Source ..................................................................... 7
Connecting the MIX BUS Jack ................................................................................... 7
Connecting an Equalizer ............................................................................................ 7
Connecting the Speakers .................................................................................................. 8
Determining Total Speaker Impedance ...................................................................... 8
Preparing the Speaker Wire ....................................................................................... 9
Connecting Only One Speaker .................................................................................. 9
Connecting Two Speakers In Series .......................................................................... 9
Connecting Two Speakers In Parallel ...................................................................... 10
Connecting Four Speakers In Series/Parallel Combination ..................................... 10
Connecting Speakers with Transformers ................................................................. 11
Connecting Power ........................................................................................................... 12
Using Your Amplifier ........................................................................................................ 12
Safety Indicators ............................................................................................................. 13
Monitoring the Sound Sources ........................................................................................ 13
Listening Safely ....................................................................................................... 13
Using an Equalizer .......................................................................................................... 13
Using the Feedback Filter ............................................................................................... 14
Troubleshooting ................................................................................................................... 15
Care and Maintenance ......................................................................................................... 16
Replacing the Fuse ................................................................ .. ....................................... 17
The FCC Wants You to Know ......................................................................................... 17
Specifications ....................................................................................................................... 18
©
2000 Tandy Corporation.
RadioShack and RadioShack.com are trademarks used by Tandy Corporation.
2
All Rights Reserved.
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ˆ
Features
Your RadioShack MPA-125 100-Watt PA
Amplifier gives you the versatility and power
you need in a professional sound system. Its
wide frequency response easily handles amplification of voice and music. Use it in meeting halls and auditoriums, at sports events, in
schools, and in the office for paging systems
– anywhere you need to deliver special announcements with excellent sound.
Your amplifier includes these features:
100-Watt Output
— provides powerful audio
output for many types of sound installations.
60–25000 Hz Frequency Response
— provides wide-ranging response for true audio
reproduction.
Lighted VU Meter
— measures the amplifi-
er’s output in decibels.
Two Mounting Options
— you can mount
the amplifier in a standard-sized audio equipment rack or on a desk, shelf, or table.
Clipping Indicator
— lights when a sound
source signal exceeds its mixing control setting.
Overload Protection
— automatically interrupts the amplifier’s power and lights an indicator if the amplifier gets too hot due to
power overload.
Master Volume Control
— lets you adjust
the overall sound level.
EQ IN/OUT Switch
— lets you connect and
use an equalizer with the amplifier.
Push-Terminal Connectors
— let you easi-
ly connect wires directly to the amplifier.
Five Individual Source Mixing Controls
—
let you mix connected sound sources individually or all at the same time.
Feedback Filter
— lets you control audio
feedback.
Read this manual carefully. It describes vari-
ous speaker connections to help you select
the best arrangement for your amplifier and
connected equipment, and explains how to
use the amplifier.
WARNING:
ard, do not expose this product to rain or moisture.
o reduce the risk of fire or shock haz-
T
CAUTION
RISK OF ELECTRIC SHOCK.
DO NOT OPEN.
CAUTION:
ELECTRIC SHOCK, DO NOT REMOVE
COVER OR BACK. NO USER-SERVICEABLE
PARTS INSIDE. REFER SERVICING TO
QUALIFIED PERSONNEL.
TO REDUCE THE RISK OF
!
Four Microphone Input Jacks
— you can
connect up to four balanced or unbalanced
microphones to the amplifier.
CD/Auxiliary Input Jack
— you can connect
a variety of audio input sources for music
and special effects.
Phones Jack
— you can connect headphones so you can hear the mixed audio in
privacy.
Features
This symbol is intended to alert you to
the presence of uninsulated dangerous voltage within the product’s enclosure that might be of sufficient
magnitude to constitute a risk of electric shock. Do not open the product’s
case.
This symbol is intended to inform you
that important operating and mainte-
!
nance instructions are included in the
literature accompanying this product.
3
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ˆ
Preparation
PRESETTING THE CONTROLS
Before you begin making connections or using your amplifier, preset the aud io input source’s
and the amplifier’s controls to avoid over-driving a channel or produci ng sudden unexpected
loud sounds.
Presetting Audio Input Devices
Set the audio input sources’ controls to these levels:
Audio Device Control Setting
Turntable Power Off
Tape Deck Power Off
CD Player Power Off
Amplifier/Receiver Power Tone Off Flat
Presetting the Amplifier
Warning:
below. After you turn on the amplifier or change the program source, adjust the control s to a
comfortable listening level.
Set the amplifier’s controls to these levels:
4
To prevent possible hearing loss, set the amplifier’s controls to the settings shown
Control Setting
POWER
POWER
MIC 1, MIC 2, MIC 3, MIC 4/PHONO, CD AUX MIN
MASTER VOLUME MIN
MIC 1
MIC 2
MIC 3
Preparation
MIC 4/PHONO
CD/AUX
Out
MASTER VOLUME
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MOUNTING THE AMPLIFIER
You can mount the amplifier in a standardsized audio equipment rack or on a desk,
shelf, or table. Be sure you place it in a location with adequate ventilation. Do not put it
on thick carpeting (which can restrict air flow)
or near a heat source such as a heat vent or
radiator (which can cause it to overheat).
ˆ
Connections
PLACING THE SPEAKERS
Speaker placement depends on your room’s
size and arrangement. We recommend you
play a wide-range recording and experiment
with speaker placement until you find the locations that result in the best sound. For the
best results, point the speakers in toward the
listeners, especially if you place speakers far
apart so their coverage areas overlap to prevent dead spots (areas not covered by the
speakers’ sound). Position the speakers
slightly above the level of the listeners’
heads (see “Connecting the Speakers” on
Page 8).
CONNECTING INPUT SOURCES
You can connect optional components such as microphones, a tuner, a turntable, or a CD player to your amplifier to expand your audio system. To prevent hum and other noise, use low-capacitance shielded cable. Your local RadioShack store carries a wide selection of audio
components and cable.
Before you make any connections, be sure
AC power cord is not plugged in.
POWER
on the front of the amplifier is out and th e
Connecting Microphones
You can connect up to four high- or low-impedance microph ones to the microphone inputs on
the back of the amplifier. Each input (labeled
and unbalanced jack. You need a microphone cord with a 1/4-inch (6.35-mm) plug to connect to
an unbalanced jack or a microphone cord with a 3-pin XLR plug to connect to a balanced jack.
MIC 1, MIC 2, MIC 3
1
/
-Inch Plug
4
3-Pin XLR Plug
Connections
MIC 4
MIC 3 MIC 2
MIC 4 MIC 3 MIC 2
, and
MIC 4
) has a balanced
MIC 1
MIC 1
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Notes:
• If your microphone’s cord is longer than 20 feet (6.01 meters), we recommend that you
connect it to a balanced jack to reduce signal hum.
• If you connect a microphone to both jacks for
you connect to the unbalanced jack has priority.
• If you connect a microphone to either
amplifier to
MIC 4
.
Connecting a Turntable
GND
PHONE/MIC 4
MIC 1, MIC 2, MIC 3
MIC 4
jack, set
Turntable
, or
PHONO/MIC 4
MIC 4
, the microphone
on the back of the
You can connect a low-level audio input source (such as a magnetic cartridge turntable) to the
L PHONO
If you connect a low-level audio input source to the
of the amplifier to
and
R PHONO
PHONO
jacks on the back of the amplifier.
PHONO
.
jacks, set
PHONO/MIC 4
on the back
To avoid a low-frequency hum, connect your turntable’s ground wire (usually black or green) to
GND
the amplifier’s
6
terminal.
Connections
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