PS Engineering
PMA450B Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-450-0600
Page 2-2
Rev. 5, August 2020
2.3.3
Audio Panel Mounting Rack Installation
Carefully slide the unit free of the tray. Set the unit aside in a safe location until needed. Install the tray using
six clip nuts (475-630-0002), and six FHP 6-32 x ½" screws (475-632-0012). The audio selector panel must
be supported at front and rear of the mounting tray.
2.3.4
Audio Panel Tray and Connector Assembly
The rack connectors mate with two 44-pin connectors in the PMA450B. The connectors are a sub-miniature
crimp-type, and require the use a hand crimp tool, from table below (or equiv.). The connectors are mounted
to the tray back plate with #4-40 screws (475-440-1038), from the inside of the tray. The connector back
shell is two pieces, (625-025-1131 and cover 625-025-1132) held together by 4 #2-56 screws (
475-256-0516)
.
This allows the back shell to be installed after the connector is populated.
Ensure that proper strain relief and chafing precautions are made during wiring and installation, using the
cable clamp (625-001-0002).
Two grounding lugs are provided, which may be attached to the rear mounting plate with 2 ea. #4-40 x ¼”
screws with captivated lock washers. These provide a convenient location to connect the shield ground ter-
minations.
Manufacturer
Crimping Tool
Positioner
Extraction tool
AMP
601966-1
601966-6
91067-1
Daniels
AFM8
K42
M24308-1
ITT-Cannon
995-0001-584
995-0001-739
91067-1
Table 2-1 Connector Pin crimping tools
Cable Harness Wiring
Referring to the appropriate Appendix, assemble a wiring harness as required for the installation. All wires
must be MIL-SPEC in accordance with current regulations. Two- and three-conductor shielded wire must be
used where indicated, and be MIL-C-27500 or equivalent specification. Proper stripping, shielding and sol-
dering technique must be used at all times. It is imperative that correct wire be used.
Refer to FAA Advisory Circular 43.13-2B for more information. Failure to use correct techniques may result
in improper operation, electrical noise or unit failure. Damage caused by improper installation will void the
PS Engineering warranty.
2.4.1
Electrical Noise
Due to the variety and the high power of radio equipment often found in today's general aviation aircraft,
there is a potential for both radiated and conducted noise interference.
The PMA450B power supply is specifically designed to reduce conducted electrical noise on the aircraft
power bus by at least 50dB. Although this is a large amount of attenuation, it may not eliminate all noise,
particularly if the amplitude of noise is very high. There must be at least 13.8 VDC present at the connector,
J2 pins 8 & 9, of the PMA450B for the power supply to work in its designed regulation. Otherwise, it cannot
adequately attenuate power line noise. Shielding can reduce or prevent radiated noise (i.e., beacon, electric
gyros, switching power supplies, etc.) However, installation combinations can occur where interference is
possible. The PMA450B was designed in an RFI hardened chassis and has internal Electromagnetic Inter-
ference (EMI) filters on all inputs and outputs.
Ground loop noise occurs when there are two or more ground paths for the same signal (i.e., airframe and
ground return wire). Large cyclic loads such as strobes, inverters, etc., can inject noise signals onto the air-
frame that are detected by the audio system. Follow the wiring diagram very carefully to help ensure a min-
imum of ground loop potential. Use only Mil Spec shielded wires (MIL-C-275000, or better). Under no
circumstances combine a microphone and headphone wiring into the same shielded bundle. Always use a 2-
or 3-conductor, shield wire as shown on the installation-wiring diagram.
The shields can be daisy-chained together, and then connected to the ground lugs mounted on the back plate
shown in Appendix B.
