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PS Engineering

PAC24 Series Audio Selector Panel and Intercom System

Installation and Operator’s Manual

200-240-0008 Page 2-6 Rev. 8, June 2003

cable clamp (625-001-0002). Secure the ground bar (430-630-0002), if desired using, #6-32 nuts (475-632-

0003) and #6-32 lock nuts (475-632-0004).

2.4 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

soldering technique must be used at all times. It is imperative that correct wire be used.

Refer to FAA Advisory Circular 43.13-2A 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 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 PAC24 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 25, of the PAC24 for the power supply to work in its designed regulation. Otherwise, it can-

not 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 PAC24 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-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 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 24H Installation

If the installation replaces a KMA-24H (series –71), and it is properly installed and wired, no other

changes are required except for removal of the keying pin. Other options not present in the KMA24H,

such as entertainment or “Swap” may require additional wiring. Speaker Power (J3, pin 7) is not required.

NOTE:

Many installation use external switching to provide crewmember isolation. These can usually be

eliminated. See below for details.

2.4.2.1 Single KMA24H -71 Installation

If the switch, labeled Isolate/Normal/Private is installed, the Primary/Secondary headphone switch should

be maintained. However, the connection to P241, Pins 21, 24, and Y should be removed.

NOTE

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