PS Engineering PMA7000B Installation Manual - Manual (Page 11)

PS Engineering
PMA7000B Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-780-0005 Page 2-4 Rev. 10, December 2012
2.4.4 Power
The PMA7000B-Series are compatible with both 14 and 28 Volt DC systems. A two (2) Amp circuit
breaker is required for 14 VDC installations, and a three (3) Amp breaker for 28 VDC aircraft. Power and
ground wires must be a twisted #18 AWG pair. Connect airframe power ground to J1 (bottom connector)
Pin Z only. No dropping resistors are required.
2.4.5 Communications Push-to-Talk
An important part of the installation is the PTT (Push-To-Talk) switches that allow the use of your air-
craft communications radio for transmissions. There are three typical configurations that can be used.
Select the case that best fits the installation. Only the person who presses their PTT switch will be heard
over the radio. If the pilot and copilot both use the PTT, the only pilot position has access to the radio.
The pilot position will have PTT control regardless of the mic selector switch or copilot PTT when the
PMA7000B is in the
OFF /E MG mode.
CASE I: PTT is built into both pilot and copilot yokes.
CASE II: PTT is in pilot yoke only. This configuration requires a modified external PTT switch plugged
into the copilot's microphone jack. (See Appendix A). When the copilot's PTT is pressed, the intercom
switches the microphone audio from pilot to copilot mic.
CASE III: No built in PTT. This requires two built in PTTs to be installed, or modified external PTT
switches to be used. Modify external PTT as required. See Appendix A.
2.4.6 Audio Panel interface
The PMA7000B is designed to interface with standard aircraft avionics, and presents a 500 receiver
impedance. For best results, a twisted-shielded cable is recommended from the avionics audio source to
the audio panel, with the shield grounded at the audio panel end.
Some avionics do not provide a separate audio low, and may introduce additional electrical noise into the
system. For best results, connect the audio low from the audio panel to the radio ground, using one con-
ductor of the twisted-shielded cable.
2.4.6.1 Speaker Load
The PMA7000-series contains a speaker amplifier. Some units with internal speaker amplifiers, such as
the King Radio KX170-series, require a resistive load to prevent damage if their speaker amplifier is not
used. Connect the speaker output from the unit to the load input on the PMA7000B (J1, pins 19 and L, 16
and M. The speaker load is 16 , 3W.
2.4.6.2 Fail Safe Connection
The PMA7000B connects the pilot microphone and headphone directly to COM 1 input when power is
removed. The headphone failsafe is the RIGHT channel, connected to the TIP of the headphone jack, to be
compatible with monaural headphones. Unswitched input #1 (Bottom Connector pin T) is also provided to
the pilot headset, right channel, in fail-safe.
NOTE: The pilot headphone MUST be wired in accordance with Appendix C, Bottom connector Pin 3 to
Pilot headphone tip (right) to ensure proper failsafe operation. Verify failsafe operation in accordance with
Section 2.11.2, step 3.
2.4.7 Com 3 Duplex (TEL) Function for Cell Phones
As installed in the standard configuration, the PMA7000B Com 3 function operates conventionally. Push-
ing the Com 3 Xmt button places the receive audio from Com 3 in the headset and applies the pilot or
copilot microphone to the Com 3 when the appropriate PTT is activated.
If J2, Pin J is connected to aircraft ground, the PMA7000B is forced into Com 3-Duplex mode. Copilot
and passenger audio as selected by hook switches are provided to the COM 3 output, the PTT for Com 3 is