Radio Shack MPA-125 - Manual (Page 11)

11 Connections
3. Connect the two pairs of speakers in
parallel. If you connected 8 ohm speak-
ers 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. Like-
wise, the total speaker impedance is 4
or 16 ohms if the speakers are 4 or 16
ohms, respectively.
4. Connect the speakers’ negative (–) ter-
minals to the COM terminal on the back
of the amplifier.
5. Connect the speaker’s positive (+) ter-
minals to the speaker terminal ( 4
Ω Ω Ω Ω , 8
Ω Ω Ω Ω
,
or 16
Ω Ω Ω Ω
) on the back of the amplifier that
matches the total speaker impedance as
calculated in Step 3.
Connecting Speakers with Trans-
formers
For the best results when you connect two or
more speakers to your system, use a line
transformer (not supplied) for each speaker.
Transformers offer these advantages:
• You can connect speakers with different
impedances without causing differ-
ences 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 trans-
former) are the inputs and are rated in watts.
The secondary taps (on the opposite side of
the transformer) are the outputs and are rat-
ed 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
power rating.
• Avoid multiple connections to the 70V
RMS and COM terminals on the back of
the amplifier.
Taps
Primary
Taps Secondary
Taps
32-2003.fm Page 11 Tuesday, March 28, 2000 10:45 AM