PS Engineering PMA7000B Installation Manual - Manual (Page 10)

PS Engineering
PMA7000B Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-780-0005 Page 2-3 Rev. 10, December 2012
NOTE: PS Engineering can make a custom wiring harness for the intercom. Call 1-800-ICS-AERO or see
www.ps-engineering.com for details.
2.4.1 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 PMA7000B 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 bottom
connector, pin 20, of the PMA7000B 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 inter-
ference is possible. The PMA7000B was designed in a RFI hardened chassis and has internal Electro-
magnetic 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-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.
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 ac-
tive 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 in-
stallation conditions, particularly with older avionics.
2.4.2 Existing KMA-24 Installation
If the installation replaces a KMA-24 (series -01, -02 or -03), the existing 44 pin connector can be used
for the bottom connector of the PMA7000B tray as is, providing it is properly installed and wired. If the
KMA 24 installation includes “External Speaker” or Internal Speaker” connections to J1 Pins X and U
respectively), these will have to be disconnected to avoid interference with the Unswitched inputs #3 and
#4.
No other changes are required except for external marker lights (see Section 3.7.2 for details). 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 for complete wiring harness details.)
The existing ground bus may be reused for radio shield connections, if it was constructed so it can be relo-
cated to the PMA7000B tray.
2.4.3 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 except to add
additional features.
2.4.3.1 Stereo PMA7000B installations into monaural PMA6000, PMA6000M.
Installations replacing PMA6000 or PMA6000M require re-wiring of the top connector to accommodate
the stereo configuration. See appendixes for detailed interconnect information.