Sigtronics ICS Load Modification Instructions
Sigtronics ICS Load Modification Instructions
Intercom Models: Sport 200
SPA-400
SPA-600
SDB-800
ST-400
ST-600
This modification is used when a Sigtronics Intercom is connected to a radio or audio panel which has a low impedance
headphone output (less than 100 ohms). This is most common with some Narco equipment (CP-135,CP-136, and MARK 12D
for example) and “home made” audio select panels.
Symptoms Are: Intercom audio volume is weak or non-existent.
Transmit function is normal on VHF radio.
Receive function is normal on VHF radio.
Verification: Disconnect the intercom headphone wire (blue) from the radio or audio panel. Make sure that the blue wire
is still connected between the intercom and all intercom headphone jacks. If the maximum intercom volume level is now
approximately 30% or more greater than when the blue wire was connected, then this modification will solve the problem.
Solution: Add a 1/4 or 1/2 watt resistor per the drawing below. The value of the resistor most commonly used is 220 ohms,
however, optimum performance can be achieved by selecting the value right for your particular installation. The resistor can
be any value between 100 and 330 ohms and is selected for the best balance between radio receive volume and intercom
volume.
The example below is for a Sport 200 intercom. The resistor modification applies to all listed intercoms.
AIRCRAFT / INTERCOM INTERFACE AREA
TO AIRCRAFT
POWER BUSS
12 /28 VDC
HEADPHONE AUDIO
TIP
POINT
AIRCRAFT
HEADPHONE
JACK
( INTERCOM
CENTRAL
GROUND
POINT )
(7) RED
(4) BLACK
INTERCOM
CIRCUIT
BREAKER
( 1 AMP )
TIP
RING
BARREL
SQ
ON
J1
TIP
AIRCRAFT
HAND MIC
JACK
TO
PILOT
PTT SW.
TO
PILOT
MIC JACK
(1) WHITE / BLACK
VOL
Sport 200
RING
12345
RADIO MIC KEY
BARREL
(3) BLUE
P1
TIP
BREAK CONNECTION
AND ADD RESISTOR
IN-LINE HERE.
PILOT
HEADPHONE JACK
AIRCRAFT RADIO
MIC AUDIO
CO-PILOT
PTT SW.
TO
(6) BROWN
INTERCOM
Sport 200
INTERCOM
(5) WHITE
(2) WHITE / RED
(10) WHITE / BLUE
J1
(11) WHITE / ORANGE
2
(1
IO
)V
T
LE
A TO
A TO
CO-PILOT
HEADPHONE JACK
BARREL
TIP
RING
TIP TO
BARREL
CO-PILOT
MIC JACK
NOTES
1. IF PILOT PTT SW IS CONNECTED TO
THE AIRCRAFT HAND MIC JACK, IT
MUST BE DISCONNECTED AND
CONNECTED TO THE WHITE / RED
WIRE AS SHOWN.
2. �
AIRCRAFT CHASSIS GROUND.
Optional Push-To-Intercom Switches
( 1 Per Headset )
Specialists in “SOUND” Management
178 East Arrow Highway, San Dimas, CA 91773 ( 909 ) 305-9399
1-12-2007 ICS-Load_1440_Mod.pdf
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