4
the portable stereo.
Suitable cables are
available at your lo-
cal Stereo or elec-
tronics store as well
as from Sigtronics.
Speaker level output
car stereo music
sources can also be
used with the SPA-
4S system. A Float-
ing Ground Adapter
or a four wire to three wire converter will have to be used be-
tween the Stereo and the SPA-4S music input. Figure 6 shows
such an adapter and how it is wired into the SPA-4S.
6. The Sigtronics SPA-4S system can be installed as shown for
use with Stereo headsets. Alternatively, monaural general avia-
tion type headsets can be used. To use monaural headsets fol-
low the installation instructions as normal except for the wiring
of the stereo headphone jacks. Use the stereo headphone
jacks supplied with the Sigtronics SPA-4S but leave the “RING”
connections open. Instead connect both headphone wires to
the “TIP” of the respective jacks. Connect both the
WHITE/GREEN and GREEN on to the TIP of the headphone
jack.
7. The Violet wire (J1 pin 12) is provided on SPA-4SN models
only for an optional Push-to-intercom function. For wiring and
additional instructions on the SPA-4SN see the “SPA-4SN
PUSH-TO-INTERCOM INSTRUCTIONS” section on page 5.
Make sure any unused wires are properly insulated and kept from
shorting to any other wires or aircraft ground. Skip down to the
“INSTALLATION CHECK OUT AND ADJUSTMENT” section on
this page.
UPGRADING A SPA INSTALLATION TO A SPA-4S
Chassis Mounting
The SPA-4S is specifically designed to easily replace a SPA-400.
The intercoms are exactly the same dimensions (1" x 2.5" x 4").
Five mounting holes are exactly in the same positions. To up-
grade, first remove the SPA-400 unit from the aircraft panel. This
is done by unscrewing the two Phillips head screws and the nut on
the ON/OFF switch. Remove the printed SPA-400 panel. Pull the
SPA-400 unit out and unplug the white connector from the wiring
harness. Finally mount the SPA-4S chassis (see Figure 2 on page
2):
1. Remove the knobs from the Volume and Squelch controls using
a 0.050" Allen wrench. Remove the nut form the ON/OFF
switch. NOTE: DO NOT REMOVE the nuts from the Volume or
Squelch (VOL/ SQ) controls.
2. Insert the SPA-4S unit from the rear of the aircraft panel with
the appropriate arrow on the unit chassis pointing upwards.
3. Install the printed SPA-4S panel and lightly thread the two 4-40
screws through the holes in intercom panel. The nuts on the
Volume/Squelch controls should fit inside the aircraft panel
holes.
4. Tighten the two screws
5. Put the knobs on the Volume and Squelch control shafts,
tighten the Allen screws, and switch nut.
Wiring Change
The wiring changes to an existing SPA installation are as follows.
Re-wire the pilot, co-pilot, and passenger(s) headphone lines. You
will not need the 4-foot intercom/aircraft interface cable (12 pin)
that comes with the SPA-4S system. You will use the SPA har-
ness already in the aircraft and the 4-foot headphone/music inter-
face cable (6 pin).
In a SPA-400 installation, the tip terminals of the pilot, co-pilot, and
passenger headphone jacks are wired to the blue wire (pin 3).
They need to be disconnected from there, the mono headphone
jacks need to be replaced with the supplied stereo headphone
jacks and connected to their respective pins on the head-
phone/music interface harness. (See Figure 4 on page 3) Make
sure that the blue wire (pin 3) is still connected to the tip of the
radio headphone line. Wire the music input as shown in Figure 4
on page 3.
MONO MUSIC
Rewire the headphone jacks as shown in the installation wiring
diagram. For mono music you can use the existing jacks. Connect
the green P2(1) and the white/green P2(2) to tip terminal of the
phone jacks.
NOTE: Make sure that the blue headphone wire from the original
SPA-400 installation is not connected to the headphone jacks tip
connection and is connected to the aircraft audio panel or radio as
shown in figure 4 on page 3.
INSTALLATION CHECK-OUT AND ADJUSTMENTS
After the unit is installed, again check that the SPA-4S unit chas-
sis, jacks, and wiring harness are clear of all aircraft operating
controls and cause no interference with them. Next, to check out
the SPA-4S unit installation, plug in all the headset mic and phone
plugs into the respective intercom jacks. Put on the pilot’s headset
and position the boom mic close to the mouth. Voice clarity is best
when the mic is at one side of the mouth and 1/4" from the lips.
To assure that the aircraft radios, pilot’s headset, and PTT switch
are connected and functioning properly, switch the SPA-4S
ON/OFF switch to the "off" position. If applicable, set the aircraft
audio panel to “Headphone” position. Then turn on the aircraft
radio(s) as usual, and verify that the pilot can hear the radios and
can transmit using his push-to-transmit switch and headset. Air-
craft radio(s) and audio panel should operate exactly as they did
before the SPA-4S system was installed. Aircraft radio reception
should also be heard in the co-pilot and passenger headsets.
There should be no intercom between headsets with the SPA-4S
unit "off".
BARREL (COMMON)
TIP (RIGHT)
RING (LEFT)
BLACK
WHITE/BROWN
WHITE/VIOLET
AIRCRAFT PANEL
NUT
FIGURE 5
RIGHT
LEFT
STEREO
+
-
+
-
+
-
+
-
R
C
R
C
C - 220 MFD, 25 VOLT CAPACITOR
J2 (5) BLACK
R - 100 OHM, 5 WATT RESISTOR
J2 (6) WHITE/VIOLET
J2 (4) WHITE/BROWN
NO
CONNECTION
TO
SPA-4S
FIGURE 6
