PS Engineering
PMA8000 Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-890-0000
Appendix A
Revision 9, June 2005
Appendix A External PTT Hook Up
Part of the installation includes the installation of PTT (Push To Talk) switches that allow the use of your
aircraft radio for communications transmissions.
There are three possible configurations ; you must select the case that best fits your installation. NOTE:
Only the person who presses their PTT switch will be heard over the radio.
CASE I
The PTT is built into the pilot and copilot
yokes
Simply install the plugs from the headset into the aircraft headphone jacks. Then use the yoke mounted
PTT to transmit. No other action is required.
CASE II
Built in PTT only on the pilot side only
This configuration requires a modified external PTT switch plugged into the copilot's mic jack. (See De-
tails Below) When the copilot's PTT is depressed, this activates an internal relay that switches the mic au-
dio to the aircraft radio from the pilot to the copilot.
Case III
No built in PTT switch at all.
Two built-in PTT must be installed, or two external, modified PTT switches will be required for both the
pilot and copilot. Modifications to the PTT are required. (See details below)
Push To Talk Modifications
When received from the manufacturer, an after-market PTT switch opens the mic audio path to the "ring"
connection of the PTT mic plug until the button is pressed. When the PTT is between the intercom and the
headset, the intercom function will not work unless the PTT switch is depressed. A simple modification
can be performed to allow proper intercom operation. NOTE: This mod does not alter normal operation.
Below are some examples of typical modifications. Contact the PTT manufacturer for more details if nec-
essary.
Procedures For David Clark PTT
Unscrew the round black plastic cover from the jack.
Connect the joined black wires to the red wire.
Replace the round black plastic cover.
Procedures for Telex PT-200
Unscrew the round black plastic cover from the jack.
Cut the red wire in the middle of the wire.
Strip both ends of the insulation.
Solder the two ends to the ground lug to the PTT jack.
Replace the round black plastic cover.
Procedures for Telex PT-300
Unscrew the round black plastic cover from the plug jack.
Remove the heat shrink material from the joined black wires.
Solder these two wires to the lug that has a white wire already soldered to it.
Replace the round black plastic cover
