PS Engineering PMA7000B Specifications download pdf (Page 10)

PS Engineering

PMA7000B Series Audio Selector Panel and Intercom System

Installation and Operator’s Manual

200-780-0005 Page 2-3 Rev. 11, February 2015

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 interfer-

ence is possible. The PMA7000B 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 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 cir-

cumstances 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 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 installa-

tion 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 respective-

ly), 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.

2.4.4 Power

The PMA7000B-Series are compatible with both 14 and 28 Volt DC systems. A two (2) Amp circuit break-

er is required for 14 VDC installations, and a three (3) Amp breaker for 28 VDC aircraft. Power and ground

wires must be a twisted #18 AWG pair. Connect airframe power ground to J1 (bottom connector) Pin Z

only. No dropping resistors are required.

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PS Engineering PMA7000B Specifications Page 10

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