PS Engineering PMA7000CAP Installation Manual - Manual (Page 10)

PS Engineering
PMA7000M-S Series Audio Selector Panel and Intercom System
Civil Air Patrol Version Installation and Operator’s Manual
200-072-0004 Page 2-3 Rev. 4, Sept. 2000
not eliminate all noise, particularly if the amplitude of noise is very high. There must be at least
nominal aircraft voltage present at the bottom connector, pin 20, of the PMA7000M-S 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 PMA7000M-S was designed in a RFI hardened chassis and has internal
Electromagnetic Interference (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 airframe that are detected by the audio system. Follow the wiring diagram
very carefully to help ensure a minimum of ground loop potential. Use only Mil Spec shielded
wires (MIL-C-27500, or better).
Radiated signals can be a factor when low level microphone signals are "bundled" with current
carrying power wires. Keep these cables physically separated. It is very important that you use
insulated washers to isolate the ground return path from the airframe to all headphone and
microphone jacks.
Adding a high-performance audio control system, particularly in conjunction with high-
performance active noise canceling headsets, cannot improve on older avionics that were
designed for cabin-speaker use. PS Engineering makes no claim that the audio panel will
provide a noise-free audio quality under all installation conditions, particularly with older
avionics.
2.5.2 Existing KMA-24 Installation
If the installation replaces a KMA-24 (part number -01, -02 or -03), the existing 44 pin
connector can be used for the bottom connector of the PMA7000M-S tray as is, providing it is
properly installed and wired. No other changes are required except for external marker lights
(see Section 3.7.2 for details), OR unless additional transceivers must be added. The "key" in
the existing connector must be located between pins 7 and 8. This connector will be used in the
bottom connector position. (See Appendix C and D for complete wiring harness details.)
The existing ground bus may be reused for radio shield connections, if it was constructed so it
can be relocated to the PMA7000M-S tray.
2.5.3 Existing PMA6000 installations
In 28-Volt aircraft, the dropping resistor may be removed; however, the 2 Amp breaker should
be changed to 3 Amp. If the old unit is stereo (PMA6000S or PMA6000MS), no rewiring is
necessary unless additional features are added.
2.5.3.1 Stereo PMA7000M-S installations into monaural PMA6000, PMA6000M.
Installations replacing PMA6000 or PMA6000M require re-wiring of the top connector to
accommodate the stereo configuration. See appendix for detailed interconnect information.