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Motorola External (Amplified) Speaker
Model:
PC board as viewed from the TOP (component) side, with
a few components shown just to assist in identification.
NSN6054A (printed on Speaker Case )
8405326T.xx (printed on AF Amp PC Board)
(this is a 12W amplifier)
NOTE: This amplified speaker utilizes a balanced audio
input... neither of the input lines are grounded. As a result,
you have two options for connecting the AF input:
1) Connect directly to the input wires (BLU & WHT) with no
attempt at input isolation. This method will work, but you may
run the risk of a possible ground loop and subsequent hum
on the audio output. Or,
2) Install a small audio isolation transformer in the AF In line.
An 8-Ohm to 300-Ohm isolation transformer works very well.
Remove the BLU & WHT wires from the PC board. Connect
the AF Input from the radio (BLU & WHT wires) to the
transformer's 8-Ohm secondary and connect the primary to
the BLU & WHT pads on the PC board. This method will also
produce more audio output than method #1.
There are two rectangular pads associated
with the BLU and WHT pads on the PC
board. If you remove the solder from these
two rectangular pads, the empty holes make
a nice attachment point for the secondary
wires from the isolation transformer. I used
a transformer from Mouser Electronics, part
#42MT010 (Xicon 350 Ohm CT : 8 Ohm
CT). I folded back the center tap wires,
wrapped the transformer in plastic electrical tape, and then
soldered the transformer directly to the under side of the PC
board allowing it to hang by the primary winding leads. I then
soldered the BLU & WHT wires back to the 8-Ohm
secondary leads and insulated them with heat shrink.
You may find it helpful to temporarily remove the blue
capacitor at C8 to facilitate installation of the isolation
transformer. Just DON'T FORGET to replace C8 when you
are finished!
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