Radio Shack MPA-50 User Manual

MPA-50 40-Watt PA Amplifier

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Owner’s Manual

Please read before using this equipment.

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Contents

Features ................................................................................................................... 3

Preparation .............................................................................................................. 4

Presetting the Controls ....................................................................................... 4

Choosing a Location .................... .... ... ....................................... ... ...................... 4

Placing the Speakers .......................................................................................... 4

Making Connections ............................................................................................... 5

Speakers .................................................................................................................. 6

Speaker Phasing ................................................................................................ 6

Determining Total Speaker Impedance .............................................................. 6

Connecting Speakers .................. .... ... ... ... ....................................... ... .... ... ......... 7

One Speaker ................................................................................................ 8

Two or More Speakers Without Transformers .......... ................................... 8

Multiple Speakers with Transformers ......................................................... 10

Controls and Operation ........................................................................................ 12

Troubleshooting .................................................................................................... 13

Care ........................................................................................................................ 14

Replacing the Fuse ............. ... ... ... .... ...................................... .... ....................... 14

Specifications .......................... .......................... ...................... ....................... ....... 15

2000 Tandy Corporation.

©

RadioShack and RadioShack.com are trademarks used by Tandy Corporation.

All Rights Reserved.

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Features

Your RadioShack MPA-50 40-Watt PA
Amplifier gives you 40 watts of solid
power for your public address (PA) sys­tem. The built-in three-band equalizer
enables you to tailor the sound to fit your
environment. Its wide frequency re­sponse easily handles amplification of
voice and music.

Its other features include:
Built-In Mixer and Preamplifier — pro-

duce the best output possible, even with
low-level audio input.

Microphone Jacks — let you connect
up to two high- or low-impedance micro­phones.

Input Jacks — let you connect auxiliary
equipment, such as a CD player, tape
deck, or receiver, for music and special
effects.

Spring-Loaded Terminals — make
speaker connection easy.

Your amplifier is ETL listed to UL stan­dards and meets all applicable FCC
standards.

WARNING:

shock hazard, do not expose this product to
rain or moisture.

CAUTION:

OF ELECTRIC SHOCK, DO NOT
REMOVE COVER OR BACK. NO USER­SERVICEABLE PARTS INSIDE. REFER
SERVICING TO QUALIFIED PERSON­NEL.

To reduce the risk of fire or

CAUTION

RISK OF ELECTRIC

SHOCK. DO NOT OPEN.

TO REDUCE THE RISK

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.

!

Master Volume Control — lets you ad-

just the overall sound level.
Individual Microphone Controls — let

you separately adjust the volume of
each microphone.

Auxiliary Volume Control — lets you
adjust the volume of the connected
equipment.

Priority Terminals — let you connect
an optional switch to cut out all other au­dio input sources and give priority to
only the

MICROPHONE 1

input.

This symbol is intended to
inform you that important oper-

!

ating and maintenance instruc­tions are included in the
literature accompanying this
product.

3Features

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Preparation

PRESETTING THE
CONTROLS

Warning:

amplifier could damage your hearing or
the speakers connected to the amplifi­er’s output.

To avoid accidentally overdriving a
channel or prematurely amplifying an
audio input, set all the amplifier’s front­panel controls to their lowest settings.

To avoid sudden audio from the input
sources, be sure all audio devices are
turned off before you connect them to
the amplifier.

A sudden high output from the

CHOOSING A LOCATION

Choose a location with adequate venti­lation. Do not place the amplifier on thick
carpeting or cushions (which can restrict
the air flow) or near a heat so urce, such
as a heat vent or radiator (which can
cause the amplifier to overheat).

Notes:

• Place the speakers so they are
mounted slightly above the listeners’
heads and pointed toward them.

• When using more than one speaker,
overlap the projection areas of the
speakers to prevent “dead” spots.

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.

4

Preparation

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Making Connections

Important: Connect all auxiliary equipment and speakers before connecting power.

PHONO L (Left) and R (Right) Input
Jacks — Connect a turntable with a

magnetic cartridge. To avoid distortion,
do not connect a high-level audio input
source to these jacks. Even though the
amplifier has
output from the amplifier is monaural.

AUX/CD L and R Input Jacks — Con­nect any high-level sound source (such
as a tape deck, CD player, receiver, or a
turntable with a ceramic or crystal car­tridge). To connect a stereo source, use
shielded audio cable (available at your
local RadioShack store); however, the
amplifier’s output is monaural.

GROUND Screw — Connect the
ground wire (usually black or green)
from your turntable to this screw to avoid
a low-frequency hum. You can also use
this screw to ground any other system
connection.

and R input jacks, the

L

PHONO/AUX/CD Switch — Select the

input source. Even if you connected
auxiliary equipment to both the
and

AUX/CD

only one source at a time.
Speaker Push Terminals — Press the

appropriate tab to open a terminal. In­sert the end of a speaker wire into the
opening, then release the tab to close
the terminal and secure the wire (see
“Connecting Speakers” on Page 7).

PRIORITY Terminals — To allow

CROPHONE 1

connect an SPST (single-pole, single­throw) switch to the amplifier’s
terminals using normal two-conductor
wire (switches and wire are available at
your local RadioShack store). Refer to
the switch’s manual for connection a nd
usage instructions.

AC Power Cord — To use AC power,
plug this cord into an AC outlet.

input jacks, you can use

to override all other inputs,

PHONO

MI-

PRIORITY

5Making Connections