PS Engineering
PMA450B Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-450-0600
Page 2-5
Rev. 5, August 2020
system to work. The photocell mounted in the unit face will automatically adjust the intensity of the push-
button annunciator LEDs.
2.4.8
Unswitched inputs
J1, pins 31 (Unsw 1), 44 (Unsw 2) 29 (Unsw 3) and J2 pin 15 (Unsw 4) are unswitched, unmuted (by trans-
mitter keying), inputs.
These inputs are presented to the pilot and copilot regardless of the audio configuration, and will always mute
the crew entertainment inputs. These 510Ω inputs can be used for altimeter DH audio, GPS waypoint audio,
autopilot disconnect tones, or any other critical audio signal.
Unswitched #1 is always presented to the speaker, plus to the crew headphones, and is available to the pilot
in fail-safe (off) mode.
Unswitched 1 & 2 are always presented to the speaker, plus to the crew headphones.
*Unswitched 3 and 4 inputs are always presented to the crew headphones but presented to the aircraft speaker
only
when the speaker is selected.
Unswitched
Input
Hear in
Fail Safe
Hear in
Crew Headset
Hear in SPR
Adjustable at installation
1
Yes
Yes
Yes
Yes
2
No
Yes
Yes
Yes
3
No
Yes
When SPR Se-
lected
Yes
4
No
Yes
When SPR Se-
lected
Yes
Table 2-3 Unswitched inputs
The audio low for unswitched #4 (J2, pin 15) should be connected to a convenient audio low. However, this
should NOT be connected to Music Low.
NOTE
Inputs 1 and 2 are fixed (1:1), and any audio level adjustments must be made at the input source. Unswitched
#3 and #4 can be adjusted at installation. Refer to Adjustments §2.7.
2.4.8.1
Additional unswitched inputs
If necessary, unused switched inputs (ADF, DME, etc.) can be converted to unswitched inputs. Contact PS
Engineering for more information.
2.4.9
"Swap" Mode
When a momentary, normally open, push-button switch is connected between pin 20 on the J2 connector and
aircraft ground, the user can switch between Com 1 and 2 by depressing this switch without having to turn
the mic selector switch. This yoke-mounted switch eliminates the need to remove your hands from the yoke
to change transceivers. The transfer of TX indication from Com 1 to Com 2 shows that the swap has been
initiated; there is no dedicated swap indicator.
2.4.9.1
Remote ICS mode control
A long press of the remote SWAP switch (>1 second) will change the intercom mode, in order
All/CREW/ISO/All, as shown on the intercom mode indicator on the PMA450B.
2.4.10
Public Address Mode
By holding the
N1
pushbutton for more than one (1) seconds, the PMA450B will be placed into public ad-
dress (PA) mode. In this mode, the pilot will be talking over the cockpit speaker when he presses his PTT
switch. Copilot will continue on the selected COM radio. The C1 & C2 Transmit indicates will go
off
in PA.
The display will include
PA
& SPR on the right side, and change to
PUBLIC ADDRESS
when the pilot’s
PTT is pressed.
