MPA-46 (320-2042) Installation Faxback Doc. # 7709
PLACING THE AMPLIFIER
Before you use your amplifier, be sure you choose a location with adequate
ventilation. Do not place the amplifier on thick carpeting (which can
restrict the air flow) or near a heat source, such as a heat vent or
radiator (which can cause the amplifier to overheat).
PRESETTING THE CONTROLS
Setting the Amplifier
Warning: A sudden high output from the 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 the amplifier's controls to the
levels shown before you connect the AC power cord or turn on
power.
Setting the Input Sources
To avoid sudden audio from the input sources, set their controls to the
levels shown before you connect their output jacks to the amplifier's
input jacks.
Audio Device Control Setting
Turntable Power OFF
Tape Deck Power OFF
CD Player Power OFF
Amplifier/Receiver Power OFF
Tone FLAT
CONNECTING AUDIO COMPONENTS TO THE AMPLIFIER
You can connect optional audio components (such as microphones, tuners,
turntables, or CD players) to your amplifier to expand your system. Your
local Radio Shack store carries a wide selection of audio components, and
speakers.
Caution: Make all the connections to the amplifier and speakers before
connecting and turning on power.
Connecting Microphones
You can connect a microphone to one or both of the amplifier's MIC 1 and
MIC 2 input jacks. The microphone(s) can be high or low-impedance and
must have a 1/4-inch plug.
Connecting a Turntable
You can connect an audio input source, (such as a ceramic cartridge
turntable or CD player), to the amplifier's L and R PHONO jacks.
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 Audio Source
You can connect an auxiliary audio input source (such as a tape deck, CD
player, or tuner) to the amplifier's L and R AUX.CD Jacks.
Connecting the Priority Terminals
You can connect a SPST (single-pole, single throw) switch to the
amplifier's PRIORITY terminals.
A switch connected to the PRIORITY terminals gives priority to the MIC 1
input by disabling all other inputs. This is ideal for paging or making
loudspeaker announcements.
You can use normal two-conductor wire up 200 feet long to connect the SPST
switch. Your local Radio Shack store sells several SPST switches and the
appropriate wire for this connection. Refer to the switch's owner's
manual for specific connection instructions.
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.
Typical Coverage
Single Speaker (Narrow Coverage)
Two Speakers (Wide Area Coverage)
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 as follows:
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.
CONNECTING THE SPEAKERS
Determining Total Speaker Impedance
Caution: A total speaker impedance that is higher than 16 ohms or lower
than 4 ohms can damage your amplifier or speakers.
Before you connect speakers to the amplifier, you must determine the total
speaker impedance. In determining the total speaker impedance, you must
first determine if you are connecting the speakers in series, parallel, or
a series/parallel combination.
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 (see
"Connecting Speakers in Series").
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 number of speakers) for a total speaker
impedance of 4 ohms (see "Connecting Speakers in Parallel").
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 = 32). This
exceeds the maximum rating.
-In parallel, the total impedance is 2 ohms (8 divided by 4 = 2).
This falls below the minimum rating.
You can achieve a proper total impedance by combining series and parallel
connections (see "Connecting Four Speakers in Series/Parallel
Combination").
Making the Speaker Connections
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 (+ to + and - to -) 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 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 -.
Remove about 1 inch of insulation from the end of each wire. Then twist
the exposed wire to secure all its strands.
Connect the speaker wire to the amplifier and the speaker(s) by pressing
down on the appropriate push terminal lever and inserting the end of the
twisted 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 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 speakers' negative (-) terminal to the amplifier's
COM terminal.
3. Connect the right speakers' positive (+) terminals to the amplifier's
4 ohms, 8 ohms, or 16 ohms terminal that matches the total speaker
impedance.
Connecting Speakers in Parallel
Follow these steps to connect speakers in parallel.
1. Connect the speakers' left and right negative (-) terminals together.
2. Connect the speakers' left and right positive terminals together.
3. Connect both speakers' negative (-) terminals to the amplifier's COM
terminal.
4. Connect both speakers' positive (+) terminals to the amplifier's
4 ohms, 8 ohms, 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 will be 4 or 16 ohms
if the speakers are 4 or 16 ohms, respectively.
4. Connect both speakers' negative (-) terminals to the amplifiers COM
terminal.
5. Connect both speaker's positive (+) terminals to the amplifier's
4 ohms, 8 ohms, or 16 ohms terminal that matches the total speaker
impedance, as calculated in Step 3.
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
re-calculate 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 35-watt output power 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) taps on the transformers' 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 TO POWER
You can power your amplifier from standard AC power by simply plugging the
supplied AC cord into a standard AC outlet.
(br/all-9/29/94)