MPA-250 250-Watt Stereo Public Address Amplifier
(320-2004)                 Connections                Faxback Doc. # 51681

Connecting an Input Source

You can connect a component such as an audio mixer or preamplifier to the 
inputs on the back of your amplifier.  Each input (labeled INPUT and INPUT 
MONO) has a balanced and unbalanced jack.  You need a shielded cable with 
a 1/4-inch (6.35-mm) phono plug to connect to an unbalanced jack or a 
cable with an RCA plug to connect to a balanced jack.  To prevent hum and 
other noise, use low-capacitance shielded cable.  Your local RadioShack 
store carries a wide selection of audio components and cable.

CAUTIONS:  You can connect audio mixers or preamplifiers to either the
           balanced or unbalanced jacks.  Do not connect input sources to
           both jacks at the same time.

           Before you make any connections, be sure POWER on the front of
           the amplifier is off and the AC power cord is not plugged in.

Unbridged Connection

If you are connecting more than one speaker on the same channel (unbridged 
connection), connect your audio mixer's or preamplifier's left and right 
output jacks to the INPUT R and INPUT L jacks on the back of the 
amplifier.  Then, make sure STEREO/MONO on the back of the amplifier is 
set to STEREO.

Bridged Connection

If you are connecting high-power speakers that can handle a power output 
of 350 watts (bridged connection), connect your audio mixer's or 
preamplifier's output jack to the INPUT MONO or INPUT L jack on the back 
of the amplifier.  Then, make sure STEREO/MONO on the back of the 
amplifier is set to MONO.

Grounding the Input Source

To avoid a low frequency hum, connect your audio mixer's or preamplifier's 
ground wire (usually black or green) to the GND terminal on the back of 
the amplifier.

Connecting Speakers

You can connect one or more 4-, 8-, or 16-Ohm speakers to the amplifier.  
You can also bridge the amplifier's channels.  This lets you use the 
amplifier with only one channel that produces a total of 350 watts.

The amplifier has two channels: A and B.  If you connect two pairs of 
speakers, follow these guidelines:

  Speakers connected to the same channel (A or B) are part of a pair and
  must be of the same impedance.

  Speakers connected to different channels (A or B) are not part of a pair
  and can be different impedances.

Most speaker terminals are color-coded or have a mark that indicates the 
terminal's polarity.  Usually, terminals with positive polarity are red or 
have a plus symbol (+), and terminals with negative polarity are black or 
have a minus symbol (-).  Phasing is correct when you connect (+) to (+)
and (-) to (-).

Preparing the Speaker Wires

Use the shortest length of wire possible to connect the speakers.  After 
placing the speakers, use this table to determine the wire length and 
choose the appropriate gauge.

     WIRE LENGTH       WIRE GAUGE

     25 feet or less   18 gauge
     Over 25 feet      16 gauge

To prepare the speaker wire, remove about 1 inch of insulation from the 
end of the speaker wire you are connecting to the amplifier.  Then twist 
the exposed wire to secure all of the wire strands.

Unbridged Connection

Use this connection if you are connecting more than one speaker on the 
same channel or if you do not have high-power speakers.

1.  Connect the speaker wires to the corresponding left and right
    speaker's positive (+) and negative (-) terminals.

2.  Connect the other end of the left and right speaker's positive (+) and
    negative (-) wires to the amplifier's corresponding SPEAKERS LEFT and
    SPEAKERS RIGHT terminals for each channel.

    To connect speaker wires to the amplifier, turn the knob on the
    terminal counterclockwise until it stops, insert the bare wire inside
    the space between the knob and the amplifier, then turn the knob
    clockwise until it stops, to secure it.

3.  Make sure STEREO/MONO is set to STEREO.

Bridged Connection

Use this connection only if you have high-power speakers that can handle a 
power output of 350 watts.

IMPORTANT:  For a bridged connection, do not connect any speaker wires to
            the black SPEAKERS terminals.

1.  Connect the speaker wires to the speaker's positive (+) and negative
    (-) terminals.

2.  Connect the other end of the speaker's positive (+) and negative (-)
    wires to the amplifier's red SPEAKERS LEFT  and SPEAKERS RIGHT
    terminals.

    Note:  SPEAKERS RIGHT (+) on the amplifier is used as a negative (-)
           terminal for a bridged connection.

3.  Make sure the STEREO/MONO is set to MONO.

Using the Switched AC Outlet

The amplifier's switched AC outlet provides a source of 120 V, 60 Hz power 
for audio equipment you connect to it.  POWER on the amplifier turns both 
the amplifier and the audio equipment connected to this outlet on or off.

Connected Power

To connect the amplifier to power, plug the attached power cord into a 
standard AC outlet.

your amplifier's fuse (located on the amplifier's back panel) protects the 
amplifier from voltage surges.  If the amplifier does not work when you 
press POWER, check the fuse.  If it is blown, see "Replacing the Fuse" in 
Faxback Doc. # 51683 to replace it.

(EB 3/4/99)