PS Engineering Audio System Installations

Theory and Practices

Disclaimer• Your PS Engineering Dealer is responsible for the product installation.

– Refer specific interface questions and procure any special tools or additional installation supplies from the PS Engineering retail dealer.

– All PS Engineering dealers have an FAA Certified Repair Station with at least a Limited Radio Rating, and are qualified to make these installations.

• If the installation is not performed by a PS Engineering dealer or a custom wire harness is not purchased, the warranty is VOIDVOID.

• Installation of an intercom in a certified aircraft in accordance with regulations may require specific knowledge, experience and tools.

– FAR 65.81 (b) A certificated mechanic may not exercise the privileges of his certificate and rating unless he understands the current instructions of the manufacturer, and the maintenance manuals, for the specific operation concerned.

• This presentation does not contain basic information about crimping, soldering, or fundamental assembly techniques. These skills are required to fabricate a wiring harness.

• Either the PS Engineering authorized dealer or PS Engineering can make a custom harness for you for products made by PS Engineering.

Why can’t we help with installation questions?

• We don’t have the expertise. We have never performed an installation, so we must rely on avionics shops that have the knowledge and tools to perform installs.

• We don’t have the necessary resources to provide the technical support necessary to aid in installations.

• To assure proper installation, we have trained our dealers about the specifics about our products. This assures that we will not have warranty costs associated with improperly installed products

Applicability

• This presentation applies to:– Intercom Installation– The intercom portion of audio panel

installation

• This does not apply to:– Radio Interface to Audio Panels– Any other avionics installation– Any wiring practice not specifically addressed

Topics

1. Overview2. Tools and Hardware Required3. Theory of shielding and overall harnesses4. The interface for the intercom5. Building the Harness for the intercom6. How to properly make shield terminations7. The Intercom Installation8. How to ground the harnesses9. Entertainment interface10. Troubleshooting

Overview• Build Harness for Installation

• Create Wire Harness per the Wiring Diagram located in the Installation Manual

• Route cables to the mounted mic and headphone jacks throughout aircraft

• Route cables to the music and telephone inputs as necessary

• Connect audio panel/intercom to power and ground• Verify power and ground continuity

• Mechanically Install Audio Panel/Intercom in panel– Note: If installing Intercom, Install Auxiliary Microphone and

Headphone Jacks • These are the jacks that will connect directly to either the

single radio or to the audio panel.• Test these jacks using a headset and in-line PTT switch

to assure you can hear and transmit over the radio

Tools and Hardware Required

• Wire Strippers (Ideal Strip Master)

• Wire Cutters

• Crimping Tool (Palatine PA1440)

• Soldering Station (WTCPT)

• Drill

• Philips Screwdriver #1

Tools

Crimping tool for PMA8000/9000-series (High Density)

Molex Crimping tool (PMA6000/7000 Series) Use “A”

Strip 18-24 AWG

HardwareJacks

• Three types– Microphone, Headphone (mono and stereo)

• Mono Phones (1/4”)– 2 Conductor

• Stereo Phones (1/4”)– 3 Conductor

• Microphone (mic) jacks – Note, the mic jack has a smaller opening than the headphone jacks

– 3 conductor– Smaller inside diameter

Wire

• All wire must be aircraft grade– Tefzel insulation for flammability requirements– Single conductor must meet MIL-STD 22759– Multiple Conductor must be shielded, and

meet MIL-STD 27500– Microphone and stereo headphones must be 3-

conductor with shield.– Mono headphone must be 2-conductor with

shield– Never use the shield to carry signals or

grounds

Wire Marking

• Identification markings should be placed at each end of the wire and at 15-inch maximum intervals along the length of the wire.

• Wires less than 3 inches long need not be identified.

• Wires 3 to 7 inches in length should be identified approximately at the center.

Raychem Solder Sleeves– Heat evenly until the

blue and white rings melt, and provide a plug on each end. avoid overheating the wire.

– Watch the wire/braid connection to see the solder fully wetting the connection.

Theory of shielding and overall harnesses

• Shield grounded at one end keeps RF out because undesired currents can’t flow.

• Braided shields grounded at one end create a Faraday RF shield.

• Stray signals seek a low impedance (Z) path to ground. The properly terminated braid shield provides that path.

Shielding

Schematic Representation3-conductor w/shield

2-conductor with shield

Shield Termination Floating Shields

Mic KeyMic Audio Hi

Mic Audio Low

Phones Audio Hi

Phones Audio Low

Uni

t Con

nect

orU

nit C

onne

ctor

Phones Audio Low

Phones Audio Hi

Mic Audio Low

Mic Audio HiMic Key

Floating ShieldsShield Termination

2-conductor with shield

3-conductor w/shield

123

45

6

6

5

32

PS Engineering Wiring Schematic

Typical Audio Installation This shows some typical shielding schematics.

Notice how in the top schematic the low is connected to a unit pin. In some PS Engineering installations, to save space, the low side is connected to the shield ground AT THE UNIT.

This is NOT the same as using the shield as the audio low.

The number of solid wires that pass trough the ungrounded end of the shield signifies the number of conductors in the cable.

The Aircraft RFI/EMI Jungle

• Countless sources of RFI/EMI Energy– Comm radios– Electric motors (flaps, trim, blower)– Switches– Alternators & generators– Strobes & beacons– Other audio systems

• Any and all will create noise in the audio system – Unless you follow manufacturer’s installation

instructions

Audio Low

• Return path for audio signals– Older avionics may not have a dedicated audio

low – use chassis ground at radio/audio panel

• Never use a shield as current carrying wire. All shields must remain un-terminated at the jack end.

• Never use airframe ground as audio return path

Ground Do and Ground Don’t• DO ground shields at one end ONLY• DO tie shields together at ONE (1) end

– Almost always the signal SOURCE

• Don’t ground the jacks mechanically• Don’t ground both ends of shield set

– even for different systems

• Don’t use the shield as an audio return wire• Don’t EVER run mic and headphone audio

in same shield (it will squeal!).

Single-point Grounding

• A designated ground on the unit or system for connecting all shield and circuit grounds.

• Designed to accept RFI and EMI and pass safely around the signal paths.

• Any change in ground potential is felt identically by all subsystems, and ignored.

Block Diagram

Music Jack

Copilot Jacks Pilot Jacks

MICPHONE MICPHONE

AUX Jacks

MICPHONE

Pass 2 Jacks Pass 1 Jacks

MICPHONE MICPHONE

PowerAircraftGround

Circuit Breaker

11-33 VDC

COM radio or Audio Panel

Aircraft Radio Headphone , Microphone, & PTT

• These are a REQUIRED part of any intercom installation. It where the Intercom is connected to the radio(s)

• Mechanical and Electrically interface assures failsafe operation.– Bypass intercom– Use if intercom is removed– Essential part of troubleshooting

For the Intercom installs, Auxiliary Jacks

AUX Jacks Schematic (for intercom installations)

Building the Harness

• Strip outer jacket• Comb out braid and fold back over jacket• Create a drain wire for the shield:

– Using heat activated LC-3 Raychem sleeves, insert a stripped “drain” wire between ring and braid.

• Connect drain wire of the shielded cable to appropriate ground point:– If necessary, daisy-chain to other “drain”

wires, or connect to designated ground pin

Wire

Shield

White

Orange Tracer Blue

Tracer

PS Engineering Harness Conventions

MicrophoneWhite – Ring – Mic AudioBlue – Barrel – Mic Audio LowOrange – Tip – Radio P-T-T

Headphone or MusicWhite – Tip – Audio (Rt)Blue – Barrel – Audio LowOrange – Tip – Audio (Lt)

Terminating Wire 

Termination CompleteSolder melted and flowed

Seals melted

Heat Shrink conforms

CrimpStrip 1/16” (depth of middle band)

Verify good crimp by pulling on the wire.

Insert and Close

Jack Wiring • Mono Headphone

– Connect Audio Hi to tip– Connect Audio Low to barrel– Do NOT connect shield

• Stereo Headphone– Connect Audio Right Hi to tip– Connect Audio Left Hi to ring– Connect Audio Low to barrel – Do NOT connect shield

• Microphone– Connect Push-to-Talk (Radio P-T-T) to tip– Connect mic audio to ring– Connect mic low to barrel– Connect low side of P-T-T to barrel– Do NOT connect shield

Pilot Phones

Anatomy of a Jack

Mic Jack

0.205” ID

Phones Jack

0.250” IDStereo Jack or

Mic Jack Layout

Ground(Barrel)

Tip

Ring

TipRing

TipRing

Schematic View (3 conductor)

Ground(Barrel)

Shield

Jack/Plug Contacts

Ring

Tip

Barrel

Hardware Installation

• Connect pilot, copilot and passenger jacks.– Verify correct intercom operation, talk

between all seats and test all modes.

• Make connection between intercom and existing (AUX) headphone and microphone jacks connected to radio/audio panel

• With audio panel/intercom off, test Fail-Safe system by transmitting and receiving on radio from Pilot Headset positon

• Turn intercom on– Verify that the radio is not keyed

• Test radio receive and transmit on pilot and copilot. Test intercom ISO and Crew function (if present).

• Secure unit, harness and jacks.

Checkout Procedure

Fail-Safe

• Connects pilot headphone and microphone to radio through a relay contact in closed position

• In fail safe when off, or power removed at breaker.

• In stereo installation, radio audio will be in one ear only

• Verify fail-safe on initial installation– If it doesn’t work, the installation is wired

incorrectly

Intercom Installation

• Drill 6 holes– 2 knobs– Switch– LED (if equipped)– 2 mounting screws

Ø0.125

Ø0.375 Ø0.265

Ø0.25

PM1000II Template

122-102-0001

Jack Installation• Drill 15/32” (0.450”) hole for each jack• Place flat insulating washer on jack and

insert from rear.• Place shoulder washer on jack so

shoulder fits into the hole.• Add nut and tighten.

– Be sure that the jack barrel does not contact the metal airframe.

– Be sure that no part of a headphone jack touches a microphone jack

Sidetone

• Audio signal from COM radio of transmission– Designed to help person regulate voice– In PS System it is passed through from the

COM

• Where did it go?– Not present in some Cessna systems

• Separate sidetone output on some radios

– Can be lost through Radio Frequency Interference (RFI) caused by improper shielding

Entertainment Inputs

• One input on standard intercoms• Two inputs on units with crew mode

– Second input active only in crew mode

• Requires a minimum audio level 1 V p-p (Line Level) compatible with portable devices– Do NOT USE speaker levels from automotive

units

• Input jacks should not be grounded– Install in plastic panel

Unswitched Inputs

• Only Available in PM3000, P/N 11931A– Two inputs for alert audio, warnings etc.

• NO unswitched inputs on other models– Kluge installations are unapproved– Some COM receivers have aux inputs

Installation TroubleshootingSymptom Possible Cause

Excessive electrical Noise in intercom Mic and or headphone jacks touching ground.

Incorrect shield connection

Intercom partially keys when turned on Mic jack miswired

Failsafe doesn’t provide headphone audio Stereo headphone jack miswired

No sidetone Not provided on com phones output

Mic and or headphone jacks touching ground.

Incorrect shield connection

Audio squeal when volume on intercom turned up

Mic and headphone signals crossed, or running in same shield

Noise in system that goes away when radio or intercom active

Music source introducing noise

Music jack is grounded

Intercom audio in one ear only Stereo headset set to stereo in mono installation