PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010
Page 2-10
Rev. 29, Sept. 2021
Engineering makes no claim that the audio panel will provide a noise-free audio quality under all installa-
tion conditions, particularly with older avionics.
2.4.2
Existing KMA 24H Installation
If the installation replaces a KMA-24H (series –71), and it is properly installed and wired, no other changes
are required except for
removal of the keying pin
. Other options not present in the KMA24H, such as en-
tertainment or “Swap” may require additional wiring. KMA-24H Speaker Power (J3, pin 7) is not required.
NOTE:
Many installation use external switching to provide crewmember isolation. These can usually be
eliminated. See below for details.
2.4.2.1
Single KMA24H -71 Installation
If the switch, labeled Isolate/Normal/Private is installed, the Primary/Secondary headphone switch should
be maintained. However, the connection to P241, Pins 21, 24, and Y should be removed.
2.4.2.2
Dual KMA24H -71 Installation
In a dual KMA24H-71 installation, we recommend that the ISO/Normal/Private switches be removed.
These switches apply a ground to logic inside the KMA24H.
THE CONNECTIONS BETWEEN THE AUDIO PANELS MUST BE LEFT INTACT. This includes Pins
V to V (Key Enable), 21 to 24 (Isolate /Isolate 22) and Y to Y (Private). PS Engineering uses these lines for
data bus communications between panels.
2.4.3
Power
The PAC24-Series are compatible with both 14 and 28 Volt DC systems. A three (3) Amp breaker is re-
quired. Power and ground wires must be a #18 AWG pair. Connect airframe power ground to J3 Pin 25
only. No dropping resistors are required.
2.4.4
Communications Push-to-Talk (single panel installation)
Unless the system is in split mode, only the person who presses their transmit PTT switch will be heard
over the radio. If the pilot and copilot both use the PTT, only the pilot position has access to the radio. The
pilot position will have PTT control regardless of the copilot PTT when the PAC24 is in the
OFF
/E
MG
mode.
2.4.4.1
Communications Push-to-Talk (Dual Panel Installation)
The PAC24 automatically senses if the other audio panel is transmitting. If communications transceivers
selected for transmit are different (Com 1 pilot, Com 3 copilot), both panels will allow simultaneous, dual
transmission (split mode). If the
same
radio has been selected for transmit on
both
audio panels, the pilot
mic will have priority, and the copilot will not transmit.
2.4.5
Audio Panel interface
The PAC24 is designed to interface with standard aircraft avionics, and presents a 500
receiver imped-
ance. 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 conduc-
tor of the twisted-shielded cable.
2.4.6
Transmit Interlock
Some communications transceivers use a transmit-interlock system. To fully utilize the Split Mode feature,
this function must be disabled. Consult that manufacturer's installation manual.