MPA-101 100-Watt  (320-2039)       Connections        Faxback Doc. # 14622
PA Amplifier

CONNECTING INPUT SOURCES

You can connect optional components (such as microphones, tuners,
turntables, or CD players) to your amplifier to expand your system.  To
prevent hum and other noise, use low-capacitance shielded cable.  Your
local Radio Shack store carries a wide selection of audio components and
connecting cable.

Before you make any connections, be sure the POWER switch is in the out
position and the AC power cord is not plugged in.

Connecting Microphones

You can connect up to four high- or low-impedance microphones to the 
amplifier's unbalanced or balanced MIC 1 - MIC 4 inputs.  The unbalanced 
inputs require a microphone cord that has a 1/4-inch plug, and the
balanced inputs require a microphone cord that has a 3-pin XLR connector.

Notes:  If a microphone cord is longer than 20 feet, we recommend that you
        use the amplifier's balanced inputs to reduce signal hum.

        If you connect a microphone to the unbalanced, 1/4-inch jack and a 
        microphone to the balanced 3-pin XLR connector, the microphone you 
        connect to the unbalanced, 1/4-inch jack has priority.

        If you connect a microphone to the MIC 4 microphone jack (either
        the balanced 3 pin XLR connector or the 1/4-inch jack, set
        PHONE/MIC 4 to MIC 4

Wiring XLR Microphone Connection: 1 = bare  2 = white  3 = black

Connecting a Turntable

You can connect a low level audio input source (such as a magnetic
cartridge turntable) to the amplifier's L and R PHONO jacks.

Note:  If you connect a low level audio input source to the PHONO jacks,
       set PHONO/MIC 4 to PHONO.

To avoid a low frequency hum, connect your turntable's ground wire
(usually black or green) to the amplifier's GND screw.

Connecting an Auxiliary Sound Source

You can connect any high-level sound source, such as a CD player, tape
deck, or tuner, to the amplifier's CD/AUX jack.

Connecting the MIX BUS jack

You can connect another MPA-101 to this one to double the size of your PA
system.  This lets you use up to eight microphones (or six microphones and
two turntables), and two auxiliary sound sources.

Use a shielded cable when phono plugs at each end to connect the
amplifiers.  Connect the cable between the two amplifiers' MIX BUS jacks. 
For the best results, do not use a cable longer than 6 feet.

Connecting an Equalizer

You can connect an equalizer or other external signal processor to the 
amplifier's EQ IN/OUT jacks.

Note:  You can also connect a tape deck to the EQ OUT jacks for recording.

CONNECTING THE SPEAKERS

You can connect one or more 4-, 8- or 16-ohm speakers to the amplifier,
with or without transformers.  To ensure equal volume from each speaker,
all the connected speakers should have the same impedance rating.

Proper phasing is important when you use more than one speaker in the same
room or area.  Out-of-phase speakers can lose up to one-half of their 
potential volume, and can have a significantly decreased bass effect.

Most speakers 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 -.

Determining Total Speaker Impedance

Before you connect speakers to the amplifier, you must determine the total
speaker impedance.

Caution:  A total speaker impedance higher than 16 ohms or lower than 4
          ohms can damage your amplifier or speakers.

In determining the total speaker impedance, you must first determine if
you are connecting the speakers in series, parallel, or a serial/parallel 
combination.

Note:  For the best results when connecting speakers (in series or
       parallel), only use speakers having the same impedance.

       Speakers are connected in series when the first speaker's positive 
       terminal is connected to the next speaker's negative terminal.

       Determine the total speaker impedance of speakers you want to
       connect in series by adding up the individual impedances of all the
       connected speakers. For example, if you want to connect two 8-ohm
       speakers in series, add 8 (the impedance of one speaker) plus 8
       (the impedance of the other speaker) for a total speaker impedance
       of 16 ohms 

       Speakers are connected in parallel when all the speakers' negative
       terminals are connected together and all their positive terminals
       are connected together.

       Determine the total speaker impedance of speakers you want to
       connect in parallel by dividing the impedance of one speaker by the
       number of speakers.

       For example, if you plan to connect two 8-ohm speakers in parallel,
       divide 8 (the impedance of one speaker) by 2 (the number of
       speakers) for a total speaker impedance of 4 ohms.

       If you are connecting more than two speakers using only series or
       only parallel connections, the total impedance might exceed the
       amplifier's maximum impedance (16 ohms) or fall below its minimum
       impedance (4 ohms).

For example, if you connect four 8-ohm speakers:

-- In series, the total impedance is 32 ohms (8 + 8 + 8 + 8 = 32).
   This exceeds the maximum rating.

-- In parallel, the total impedance is 2 ohms (8 / 4 = 2).
   This falls below the minimum rating.

You can achieve a proper total impedance by combining series and parallel
connections.

Preparing the Speaker Wire

Use the shortest length of wire possible to connect the speakers.  After 
placing the speakers, determine the wire length and choose the appropriate
gauge size:

Wire Length       Wire Gauge
25 feet or less   18-gauge
Over 25 feet      16-gauge

Note:  If you connect speakers without transformers, the speaker wire
       should be no longer than 50 feet.

To prepare the speaker wire, remove about 1 inch of insulation from each
end of the speaker wire.  Then twist the exposed wires to secure all of
the wire strands.

To connect speaker wire to the amplifier, press down the appropriate push
terminal lever on the amplifier and insert the end of the wire into the 
terminal's hole.  Then release the lever to secure the wire.

Connecting Only One Speaker

Connect the speaker's negative (-) terminal to the amplifier's COM
terminal.  Then connect the speaker's positive (+) terminal to the terminal
that matches the speaker's impedance (4 Ohms, 8 Ohms, or 16 Ohms).

Connecting Two Speakers in Series

Follow these steps to connect speakers in series.

1.  Connect the left speaker's positive (+) terminal to the right
    speaker's negative (-) terminal.

2.  Connect the left speaker's negative (-) terminal to the amplifier's
    COM terminal.

3.  Connect the right speakers' positive (+) terminal to the amplifier's 
    4 Ohm, 8 Ohm, or 16 ohms terminal that matches the total speaker
    impedance.

Connecting Two Speakers in Parallel

Follow these steps to connect speakers in parallel.

1.  Connect both speakers' negative (-) terminals together.

2.  Connect both speakers' positive (+) terminals together.

3.  Connect both speakers' negative (-) terminals to the amplifier's COM
    terminal.

4.  Connect the speakers' positive (+) terminals to the amplifier's 4 Ohm, 
    8 Ohm, or 16 Ohms terminal that matches the total speaker impedance.

Connecting Four Speakers in Series/Parallel Combination

Follow these steps to combine series and parallel connections.

1.  Group the four speakers into two pairs.

2.  Connect each pair of speakers in series.  If you connected 8-ohm
    speakers, the total impedance of each pair is 16 Ohms (8 + 8 = 16).

3.  Connect the two pairs of speakers in parallel.  If you connected 8-ohm
    speakers the total impedance of both pairs is 8 ohms (16 / 2 =8).

    Note:  If each of the four speakers is 8 ohms, the total speaker
           impedance of the combined series/parallel connection described
           above is also 8 ohms.  Likewise, the total speaker impedance is
           4 or 16 ohms if the speakers are 4 or 16 ohms, respectively.

4.  Connect the speakers' negative (-) terminals to the amplifier's COM 
    terminal.

5.  Connect the speakers' positive (+) terminals to the amplifier's 4 ohm, 
    8 ohm, or 16 ohms terminal that matches the total speaker impedance.

Connecting Speakers with Transformers

For the best results when you connect two or more speakers to your system,
you can use a line transformer (such as Cat. No. 32-1031, not supplied)
for each speaker.

Transformers offer these advantages:

*  You can connect speakers with different impedances without causing 
   differences in output between the speakers.

*  You can add or remove a speaker from the system without having to 
   recalculate the entire system's impedance.

*  You can reduce signal loss when you use speaker wire over 50 feet long.

Line transformers have several connectors called taps.  The primary taps
(on one side of the transformer) are the inputs and are rated in watts.
The secondary taps (on the opposite side of the transformer) are the
outputs and are rated in ohms.

Cautions:  Before you connect the speakers, be sure the total wattage of
           the primary tap you intend to use does not exceed the
           amplifier's maximum 100-watt output rating.

           Avoid multiple connections to the amplifier's 70V and COM
           terminals.

Follow these steps to connect speakers with transformers

1.  Connect a wire from the amplifier's 70V terminal to the transformer's 
    desired primary tap (10, 5, 2.5, 1.25 or 0.62 watts).

    Note:  Usually, each speaker in a system uses the same wattage tap.
           If you want a particular speaker to have a higher volume level,
           use a higher wattage tap on its transformer.

2.  Connect a wire from the amplifier's COM (common) terminal to the C
    (common) tap on the transformer's primary side.

3.  Connect a wire from the speaker's positive (+) terminal to the
    transformer's secondary tap that matches the speaker's total impedance
    (4 ohms, 8 ohms, or 16 ohms).

4.  Connect a wire from the speaker's negative (-) terminal to the C
    (common) tap on the transformer's secondary side.

CONNECTING POWER

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

Your amplifier's fuse (located on the amplifier's back panel) protects the
amplifier from voltage surges.  If the PROTECTION indicator does not light
when you press POWER, check the fuse.  

Note:  The PROTECTION indicator turns off after a few seconds.


(SP/ir-08/31/95)

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