Northern Airborne Technology PA700 User Manual

Installation and Operation Manual

PA700 Series

High Power Voice Amplifier

SM44

ISSUE 4.02

Northern Airborne Technology Ltd.

1925 Kirschner Road

Kelowna, BC, Canada.

V1Y 4N7

Telephone [phone]

Facsimile [phone]

Issued on the authority of Northern Airborne Technology Ltd.

Copyright 2003

PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

Prepared By: Checked By: Approved By:

The status of this installation and operation manual is controlled by issue shown on the title page. The
status of each section is controlled by revision shown in the footer of each page. All revisions affecting
sections of this manual have been incorporated into the latest issue.

ISSUE/REVISION RECORD

Manual Issue

Number

4.02 Section 2 Rev: 1.01 Updated with the latest drawings. Mar 10, 2009

Section

Revision Number

Revision Description Issue Date

4.01 Section 1 Rev: 1.00
Section 2 Rev: 1.00
Section 3 Rev: 1.00

Update to current templates.

Updated Section 2 with the latest

drawings.

Aug 13, 2008

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

Table of Contents

Section Title Page

1. Description

1.1 Introduction 1-1

1.2 Product Description 1-1

1.3 Design Features 1-1

1.4 Specifications 1-2

1.4.1 Electrical Specifications 1-2

1.4.2 Physical Specifications 1-2

1.4.3 Environmental Specifications 1-3

1.5 Auxiliary Components 1-3

1.5.1 Control Panel 1-3

1.5.2 Microphone 1-3

1.5.3 Loudspeakers 1-4

1.5.4 Power Supplies 1-5

2. Installation

2.1 Introduction 2-1

2.2 Unpacking and Inspection 2-1

2.2.1 Warranty 2-1

2.3 Continued Airworthiness 2-1

2.4 Installation Procedures 2-2

2.4.1 Cautions 2-2

2.4.2 Cabling and Wiring 2-2

2.4.3 Ground Site Selection 2-3

2.4.4 Aiborne Installation 2-3

2.4.5 Remote Installation 2-3

2.4.6 Post Installation Checks 2-4

2.5 Accessories 2-5

2.5.1 Dummy Load 2-5

2.5.2 Meter Test Set 2-5

2.5.3 Protective Circuit Test Unit 2-5

2.5.4 Paralleling Transformers 2-5

2.5.5 Remote Controls 2-5

2.5.6 Tape Recorders/Players 2-5

2.6 Accessories Required But Not Supplied 2-6

2.6.1 Power/Speaker Kit 2-6

2.6.2 Recorder Input Kit 2-6

2.6.3 Microphone Input Kit 2-6

2.6.4 Remote Input Kit 2-7

2.7 Installation Drawings 2-7

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

Section Title Page

3. Operation

3.1 Introduction 3-1

3.2 General Information 3-1

3.3 Controls and Indicators 3-1

3.3.1 POWER Switch 3-1

3.3.2 GAIN Control 3-2

3.3.3 Push-to-Test Lamps 3-2

3.3.4 Resetting the Protective Circuit 3-3

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

Section 1 Description

1.1 Introduction

Information in this section consists of product description, design features and specifications for the
PA700 Series High Power Voice Amplifier. All derivative product information shall be contained in the
applicable manual supplement, which may be obtained from NAT as required.

Review all notes, warnings and cautions.

1.2 Product Description

The completely transistorized PA700 Series provides the basis for a portable, high gain, compact, tactical
sound system. It is designed to provide point-to-point dissemination of sound in application use over land,
water or from the air. The maximum useable range is greater than one mile when operated from a
favorable vantage point. The maximum rated audio power output is 700 watts with 28 Vdc input power.

Note: In airborne applications, the amplifier is normally remote-mounted in the avionics bay and the

PA700 Series controls are not operator accessible. Any necessary adjustments must be made at
the time of installation.

1.3 Design Features

The PA700 Series amplifier is a 700 watt completely transistorized unit constructed in a rug ged, black
anodized, aluminum chassis. Its reliability is enhanced by conservative design and a unique built-in
protective circuit, which shuts off the amplifier whenever excessive input or operating conditions threaten
to impair vital circuit elements.

The PA700 Series contains protective circuits, which operate to protect the semiconductor components
from the following conditions:

a) Reverse polarity
b) Excessive current or voltage
c) Internal or external short circuits

When the problem is transient or cleared, the protective circuit resets by the simple operation of the
power switch.

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

1.4 Specifications

1.4.1 Electrical Specifications

Input Power

Input Signals

Output Signals

Supply Voltage +24 to +36 Vdc normal
+40 Vdc max.

Supply Impedance <0.05Ω
Supply Current 1.0 A @ +28 Vdc (no signal)

35 A max. @ +28 Vdc (full power out)
8 A average @ +28 Vdc (voice operation)

The signal levels shown below are required for full amplifier drive at the points and impedances
shown.

JACK PINS IMPEDANCE INPUT LEVEL

MIC A-C
REC B-C
REC A-C

Output Power 700 watts into 1.4 Ω, with a 5 mVrms, 1 kHz signal applied to the

microphone input.

Output Load Impedance 1.4 Ω each channel.
Amplifier shut-down if load <1 Ω.

Frequency Response <3 dB over 300 to 10,000 Hz
Harmonic Distortion ≤10% at 40% rated power, with 1000 Hz sine wave input.

150 Ω ±15 Ω
600 Ω ±55 Ω

2000 Ω ±150 Ω

0.005 Vrms

0.5 Vrms

1.0 Vrms

1.4.2 Physical Specifications

Up to Serial No. 1075

Serial No. 1076 and up

Height 5.68" (144.3 mm) 5.78" (146.8 mm)
Depth 10.00" (254.0 mm) 10.00" (254.0 mm)
Width 8.75" (222.3 mm) 8.75" (222.3 mm)
Weight 9.88 lbs (4.485 kg) 9.9 lbs (4.54 kg)

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1.4.3 Environmental Specifications

Temperature -40 to +70°C
Altitude 35,000 feet

1.5 Auxiliary Components

The PA700 Series amplifier is designed to operate with specific compatible components to form an
effective sound system.

1.5.1 Control Panel

1.5.1.1 AA21

The AA21 Cabin PA control unit is designed to provide centralized control for an aircraft’s internal and
external PA systems. The unit is panel mounted with an illuminated NVIS Green B compliant faceplate
and a front panel switch to provide selection of the various operational modes. The AA21 provides two
low level audio signal outputs that drive the input on remote mounted power amplifiers. One output is
designed to drive the PA110/220 series amplifiers and the other output is designed to drive the
PA250/700 series amplifiers.

1.5.1.2 AA22

The AA22 PA/Siren control unit is a compact, self contained, Dzus mounted unit for use with the PA250
and PA700 series audio power amplifiers. It has a low level output rated at 500 mVrms. It provides a
centralized control for external audio paging and siren functions.

1.5.1.3 PM01-001

The PM01-001 is a remote control device designed as the operating station for a high power audio
system. The PM01-001 is equipped with two decibel meters which make it ideal for monitoring either one
or two power amplifiers.

1.5.2 Microphone

1.5.2.1 PM03-002

The PM03-002 is a hand-held, dynamic and noise-cancelling microphone with a push-to-talk button. It
comes with a coiled retractable cable and connector for direct connection to the amplifier or remote
control unit such as the PM01-001.

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

1.5.3 Loudspeakers

Various types of loudspeaker arrays can be used in sound systems using the PA250/700 amplifiers.
They are identified by the style and number of drivers (and bells) in each speaker array as shown in
Table 1. As a guideline for system configuration, there should be a minimum of 1 speaker driver/bell
assembly for each 100 watts of amplifier power.

Part No. Description

TS92-02XN Standard two-bell array with drivers
TS92-04XN Standard four-bell array with drivers
TS93-04XN Standard four-bell cloverleaf array with drivers
TS94-04XN Standard four-bell mini speaker array with drivers

Table 1

Speaker Arrays
Each PA700 Series Amplifier has two loudspeaker outputs and easily supports two 4-bell arrays.
For comparison, the efficiencies of the four-bell and six-bell speakers relative to the two-bell are shown in

Table 2 (assuming the same input power is delivered to each type).

Part No. Description Efficiency

TS92-02XN Standard two-bell array with drivers 100%
TS92-04XN Standard four-bell array with drivers 195%
TS92-06XN Standard six-bell array with drivers 285%

Table 2

Efficiencies

The higher efficiency rating is due to more concentrated sound patterns and lower, more efficient powe r
conversion at each speaker driver. The larger speakers can also accept more p ower from the amplifying
system and may show an even better efficiency rating than these figures indicate.

1.5.3.1 TS92-02XN

The two-bell speaker array is widely used in airborne applications where its light weight and small size
are important considerations. While its output efficiency is not equal to that of the larger loudspeaker
types, it performs well on small and medium-sized aircraft. The size and weight of the two-bell speaker
often permits it to become a permanent installation in the aircraft.

1.5.3.2 TS92-04XN

The four-bell loudspeaker is almost universally chosen for portable sound systems. The greater efficiency
compensates for the additional weight compared to the two-bell speaker.

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1.5.3.3 TS92-06XN

The six-bell speaker array is most often used for fixed installations where size and weight are of minor
importance but the need for maximum radiated power is primary. The six-bell speake r is also used in
larger aircraft with higher-powered amplifying systems.

1.5.3.4 Multiple Speakers

The four-bell loudspeaker, TS92-04XN is designed to be assembled in groups of two, four or more. Thi s
permits the use of multiple amplifying systems for higher sound levels and greater distance.

1.5.4 Power Supplies

Power can be supplied by storage batteries, electronic supplies or vehicle/aircraft power systems. Vehicle
supplies of 24 – 28 Vdc are an obvious choice for most airborne/mobile in stallations. The 12 – 14 Vdc
supply of the commercial vehicle can not be used.

In the hand-pack series, sealed nickel cadmium cells are used. Adding extra cells can almost double the
available power.

Electronic power supplies are frequently used in maintenance shops and fixed installations. A minimum
requirement would be a well regulated supply of 20 – 40 Vdc at 25 A.

1.5.4.1 VR33-002 Power Converter

The VR33-002 is a power conversion device designed to increase the nominal 28 Vdc aircraft voltage to
33 Vdc using high speed switching DC-DC conversion. The VR33-002 is design ed to be used with the
PA700 Series Audio Power Amplifier.

Section 1 ends

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

Section 2 Installation

2.1 Introduction

Information in this section consists of unpacking and inspection procedures, installation procedures, post­installation checks and installation drawings for the PA700 Series High Power Voice Amplifier.

Review all notes, warnings and cautions.

2.2 Unpacking and Inspection

Unpack the equipment carefully and locate the warranty card. Inspect the unit visually for damage due to
shipping and report all such claims immediately to the carrier involved. Check that all items listed below
are present before proceeding and report any shortage immediately to your supplier:

- Warranty Card

- Operators Manual

- Certificate of Conformity or Release Certification

2.2.1 Warranty

All Northern Airborne Technology Ltd. products are warranted for 2 years from date of installation by an
authorized NAT dealer, to be free of defects in workmanship or performance. This warranty covers all
materials and labour, but is exclusive of any transport to deliver the defective unit to and from NAT or its
designated warranty repair center, or any labour to remove or re-install the defective unit in the aircraft.
Contact NAT for any questions regarding this warranty, its applicability to your units and/or for return
authorization. NAT is the final arbitrator concerning warranty administration. Units which have been
physically damaged, burned, immersed in water or otherwise abused beyond the scope of normal use will
not be considered for warranty. WARRANTY IS VOID UNLESS THE PRODUCT IS INSTALLED BY AN
AUTHORIZED NAT DEALER. Product for which a warra nty card is not returned shall be warranted from
date of manufacture.

2.3 Continued Airworthiness

Maintenance of the PA700 Series High Power Voice Amplifier is ‘on condition’ only. Periodic maintenance
of this product is not required.

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2.4 Installation Procedures

2.4.1 Cautions

Use of a fully floating audio wattmeter or transformer coupled meter is

recommended. Always check ADF and compass calibration after installing external

speakers or ‘PA’ amplifiers. Significant single cycle errors may be caused by the

concentration of steel and magnetic material.

Use shielded cable exactly as shown and ground as indicated. All audio installations

can be severely degraded by incorrect wiring and shielding. Unusual buzzes, hums

or other background audio are symptomatic of multiple grounds, or noisy external

systems such as blowers or pumps sharing wiring with the audio system. Never

operate this unit below its rated impedance.

When a remote control unit is used, all signal inputs must be made at that unit and a

cable of appropriate length will be necessary to connect it to the amplifier.

Precautions are necessary when external signals, such as intercom, radio or

recorders are used. The high gain of the amplifier requires care to prevent feedback

or crosstalk. Ground loops and stray currents in the input line must be eliminated.

CAUTION:

2.4.2 Cabling and Wiring

All wire shall be selected in accordance with the original aircraft manufacturer's Maintenance Instructions
or AC43.13-1B Change 1, Paragraphs 11-76 through 11-78. Unshielded wire types shall qualify to
MIL-W-22759 as specified in AC43.13-1B Change 1, Paragraphs 11-85, 11-86, and listed in Table 11-11.
For shielded wire applications, use Tefzel MIL-C-27500 shielded wire with solde r sleeve s (fo r shield
terminations) to make the most compact and easily terminated interconnect. Follow the connector map in
Section 2.7 as required.

Allow 3" from the end of the shielded wiring to the shield termination to allow the connector hood to be
easily installed. Reference the interconnect drawing in Section 2.7 for shield termination details.

Maintain wire segregation and route wiring in accordance with the original aircraft manufacturers
Maintenance Instructions.

Unless otherwise noted, all wiring shall be a minimum of 22 AWG, except power and ground lines, which
shall be a minimum of 20 AWG. Reference the Interconnect drawing for additional specifications. Che ck
that the ground connection is clean and well secured, and that it shares no path with any electrically noisy
aircraft accessories such as blowers, turn and bank instruments or similar loads. Power to this unit must
be supplied from a separate circuit breaker or fuse (fast blow), and not attached to any other circuit
breaker without additional protection. Verify that the selected circuit breaker size and wire gauge are
adequate for the installation using the techniques specified in AC43.13-1B Change 1, Paragraphs 11-47
through 11-51 and 11-66 through 11-69.

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2.4.3 Ground Site Selection

Sound waves transmitted through air are strongly affected by wind, weather, time of day and intervening
objects. Satisfactory sound projection over great distances is possible from a well-situated operating site
that can take maximum advantage of these natural elements.

Optimum location of the loudspeakers is the prime controlling factor in site selection. This is especially
important when maximum projection is required.

An operating location with a line-of-sight observation of the target objective is desirable. For example, a
hillside location with the loudspeakers directed down or across the valley would be ideal. Sound carries
well across water and consequently advantage can be taken of a river or a lake to improve sound
transmission. It is preferable to locate upwind of the target in order to benefit from the carrying power of
the wind. Whenever possible, the site should be free of foliage or other obstructions for several hundred
yards in front of the loudspeakers.

Directional sound bends away from warm surfaces. For example, transmissions over warm pa vements
attenuate rapidly with distance, as the sound ‘curls upward’ into the cooler upper air.

2.4.4 Airborne Installation

Experience shows that sound projection from fixed wing or rotor aircraft is possible up to 2 miles slant
range. If a circling course is planned, the loudspeakers should point horizontally alongside or at right
angles to the airframe. This permits the bank of the aircraft or the downward thrust of rotor blades to
direct the sound beam toward the ground target. To reduce air resistance, the speakers may be mounted
in an open doorway or fitted into a streamlined pod. From a hovering helicopter, intelligibility is improved
by focusing the directional sound to an area outside the rotor blast.

When an input audio line from an intercom, radio, recorder, etc. to REC input is used, precautions are
necessary. The high gain of the amplifier requires care in prevention of feedback. Complete elimination of
ground loop and stray currents in the input line is mandatory. This may mean an isolation transformer is
necessary, if not otherwise provided by the signal source. Refer to Dwg No. AA22\492\403-1 for details of
an aviation-specific interconnect.

Shielding the microphone from direct sound waves from the speakers prevents acou stic feedback. This
may be achieved using an enclosure, or by operating at a considerable distan ce behind the speaker
pattern.

Multiple speakers require correct phasing, otherwise sound cancellation will greatly reduce the proje cted
power. The proper phasing is provided by the cables supplied. If any repairs or re-cabling are required,
the wiring should be checked from Dwg No. PA700\407-0.

2.4.5 Remote Installation

For installations where the Audio Power Amplifier will be remote mounted, it is recommended that the
knob be removed from the GAIN control and be replaced with the compression fitting (NAT Part No.
25-01-002, Smith p/n 181) supplied in the PAREC-IKS and PAMIC-IKS install kits. Do not remove the nut
that secures the GAIN potentiometer to the control panel. Once the compression fitting is installed on the
bushing of the potentiometer, set the GAIN control to the desired setting then carefully tighten the
compression fitting on to the shaft of the GAIN control potentiometer.

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2.4.6 Post Installation Checks

The PA system is not intended to be operated in a linear volume manner (i.e., it is not like a stereo
system). The PA is designed to provide high levels of audio power under difficult conditions and does so
by sacrificing some of the high fidelity for a higher average power output. The volume control on the
AA21/AA22 is not intended to provide linear operations from the PA system and will result in broken and
sporadic output from the PA when insufficient levels are delivered to the AA21/AA22 and/or to the PA700
unit from the AA21/AA22.

For most RADIO and PA (voice) operations, it is suggested that the AA21/AA22 volume control be set to
maximum (fully cw). If the system is overdriving, reduce the AA21/AA22 volume setting.

To check the system, the aircraft must be moved outside and away from as many reflective surfaces as
possible. It is not recommended to operate the PA microphone on the ground, as a high risk exists for
audio coupling and feedback. However, if the test is to be conducted on the ground, the aircraft should be
positioned on a grassy surface to help reduce the distortion produced by sound reflected from con crete or
asphalt. It is also beneficial to stuff the speaker projectors with soft rubberized foam to reduce the risk of
feedback and distortion.

Note: Advise all nearby personnel that PA system tests are to be conducted.
Start by checking the Siren Circuit for proper operation and tone/rate adjustment. The Siren always

operates at 100% output from the AA21/AA22 and should drive the PA's to full output on audio peaks.
The Level trimpot(s) of the AA21/AA22 will be set at the factory to provide rated output at full front panel
volume control adjustment.

Once the siren operation is satisfactory, you may try RADIO operations through the AA21/AA22. To
achieve full output capability from the AA21/AA22, a signal of 2.5 Vrms at 1 kHz must be delivered to the
AA21/AA22 radio audio input and the AA21/AA22 volume must be set to maximum. Lower levels of input
signal or volume settings will result in poor output audio (very broken).

For PA (voice) tests, it is best that the aircraft is flown in an approximately 200 foot hover and commands
are given to a human ground target for visual response to the commands. Remember, the human target
should be positioned in the area that the speaker system is designed to project the audio to. This will
depend on speaker orientation and the height "above ground level" (AGL) of the aircraft. To achieve the
best operation, all voice commands must be spoken slowly and clearly, with extra emphasis on each
word.

Note: Remove all sound absorbing material from the speakers prior to flight.
To determine the operational capability of the system, put the aircraft in a hover and with the target

properly positioned, provide PA instruction to the target to accomplish a certain task that will give visual
cue to the flight crew that the target has understood the instructions (i.e., "touch your head", "sit down",
"turn around", etc.).

Upon satisfactory completion of all performance checks, make all required log book entries, electrical
load, weight and balance amendments and other documentation as required by your local regulatory
agency before releasing the aircraft for service.

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2.5 Accessories

A range of accessories are available for testing and complementing the sound system.

2.5.1 Dummy Load

The TL-PA2 is a 2 Ohm resistive load with a three foot cable and type MS3106A-16-11P connector for
ready substitution in the speaker circuit or for connecting to the Meter Test Unit. One dummy load should
be used per channel. The use of resistive dummy load facilitates testing and power measurements,
especially when ‘quiet’ operation is desirable.

2.5.2 Meter Test Set

The TL-PA4 Meter Test Set is a convenient test unit complete with connectors and cables for inserting
into the power circuits of an amplifier and measuring both the DC current drawn and AC voltage
generated across the load. The load may be either the speakers or the TL-PA2 dummy load (checks one
channel at a time).

2.5.3 Protective Circuit Test Unit

A Protective Circuit Test Unit is available to test the protective circuit so that its proper adjustment is
assured. This unit, used with the TL-PA2 dummy load, provides GO/NO GO limits for correctly setting the
trip level.

2.5.4 Paralleling Transformers

Paralleling transformers are available for driving up to four amplifiers from the same audio signal source.

2.5.5 Remote Controls

Units may be obtained to control and/or monitor between one and eight amplifiers in parallel. All remote
units provide audio gain control and on-off power switching. A special junction box located at the
amplifiers is required in multiple amplifier systems for cable terminations and control functions. Aviation
specific configurations and other information are available upon request.

2.5.6 Tape Recorder/Players

Cables and adapters are available to interface tape recorders with the high powered voice amplifier
systems.

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PA700 Series High Power Voice Amplifier

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2.6 Accessories Required But Not Supplied

Installation kits are required to complete the installation. They consist of the following:

2.6.1 Power/Speaker Kit

This kit is used for the Power/Speaker connection. For a straight connection use PAPWR-IKS and for a
right angle connection use PAPWR-IKSR.

PAPWR-IKS consists of

Quantity Description NAT Part No.

1 MS 5 Pin Female Straight Sealed Solder Cup 20-42-001

PAPWR-IKSR consists of

Quantity Description NAT Part No.

1 MS 5 Pin Female 90° Sealed Solder Cup 20-39-005

2.6.2 Recorder Input Kit

This kit is used for the Recorder input connection. For a straight connection use PAREC-IKS and for a
right angle connection use PAREC-IKSR.

PAREC-IKS consists of

Quantity Description NAT Part No.

1 MS 3 Pin Female Straight Sealed Solder Cup 20-42-003
1 Nut, Shaft Locking ¼" 25-01-002

PAREC-IKSR consists of

Quantity Description NAT Part No.

1 MS 3 Pin Female 90° Sealed Solder Cup 20-39-003
1 Nut, Shaft Locking ¼" 25-01-002

2.6.3 Microphone Input Kit

This kit is used for the Microphone input connection. For a straight connection use PAMIC-IKS and for a
right angle connection use PAMIC-IKSR.

PAMIC-IKS consists of

Quantity Description NAT Part No.

1 MS 3 Pin Female Straight Sealed Solder Cup 20-42-003
1 Nut, Shaft Locking ¼" 25-01-002

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

PAMIC-IKSR consists of

Quantity Description NAT Part No.

1 MS 3 Pin Female 90° Sealed Solder Cup 20-39-003
1 Nut, Shaft Locking ¼" 25-01-002

2.6.4 Remote Input Kit

This kit is used for the Remote input connection. For a straight connection use PAREM-IKS and for a right
angle connection use PAREM-IKSR.

PAREM-IKS consists of

Quantity Description NAT Part No.

1 MS 7 Pin Female Straight Sealed Solder Cup 20-42-007

PAREM-IKSR consists of

Quantity Description NAT Part No.

1 MS 7 Pin Female 90° Sealed Solder Cup 20-39-007

2.7 Installation Drawings

DOCUMENT REV. DESCRIPTION TYPE SERIAL NO.
AA21-400

AA21\400\403-0 1.01 Cabin PA System Interconnect All

AA22-492

AA22\492\403-2 1.01 PA / Siren System 700 Watt Interconnect Up to 3844
AA22\492\403-2 1.10 PA / Siren System 700 Watt Interconnect 3845 and up

PA700

PA700\407-0 1.01 PA700 Amplifier Cabling Diagram All

PA700-001

PA700\001\407-0 1.00 700 Watt System Cabling Diagram All
PA700\001\407-1 1.00 1400 Watt System Cabling Diagram All
PA700\001\407-2 1.00 2100 Watt System Cabling Diagram All
PA700\001\922-0 1.00 Audio Power Amplifier Mechanical Installation Up to 1075
PA700\001\922-0 2.00 Audio Power Amplifier Mechanical Installation 1076 to 2496
PA700\001\922-0 2.10 Audio Power Amplifier Mechanical Installation 2497 and up

Section 2 ends following the above documents

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PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

Section 3 Operation

3.1 Introduction

Information in this section consists of functional and operational procedures for the PA700 Series High
Power Voice Amplifier.

3.2 General Information

The PA700 Series is built within an aluminum chassis, which provides a rugged case and an excelle nt
heat sink. Removable side panels protect the power components mounted between the cooling fins from
accidental contact with metallic objects. These panels are easily removed to gain access to the
components. Operating features are the Press-to-Test indicator lamps, the gain control, the microphone
and recorder input connectors, the POWER switch and the power-input / speaker-output connectors.

3.3 Controls and Indicators

Controls and indicators are shown in Figure 1 and will be described in more detail in this section.

POW ER Switch

PUSH-TO-TEST

Lamps

GAIN C o ntro l

Figure 1: Controls and Indicators

3.3.1 POWER Switch

The PA700 Series is switched on by setting the POWER switch to the ‘up’ position (ON).

Section 3 Rev: 1.00 Issue 4 Page 3-1

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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIR BORNE TECHNOLOGY LTD.

PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

3.3.2 GAIN Control

The GAIN control is a rotary switch used to adjust the gain of the unit. For specific operating information,
see sections 3.3.2.1 and 3.3.2.2 below.

3.3.2.1 Operation with Microphone

For microphone operation the ‘GAIN’ control is adjusted clockwise from OFF. If feedback is a problem it
may be necessary to reduce the input ‘Gain’ control or preferably, improve the sound shielding of the
microphone position.

Loudspeakers will overheat with a continuous signal at full power. Voice operation will generate less heat,
and pauses between words result in a low-duty cycle.

3.3.2.2 Operation with Recorder

When a recorder or other external sound source is to be operated with the amplifier, connection is mad e
to the recorder (REC) input connector.

The ‘GAIN’ control is rotated counterclockwise from the OFF position to increase the recorder input
signal. Pins B - C will be used for a 600 Ohm source and Pins A - C will be used for a 2000 Ohm source
as shown on the amplifier panel.

If the recorded sound is voice, the correct input level is adjusted in the same manner as for microphone
operation. If the recorded sound is music, it is advisable to operate at a reduced ‘GAIN’ control setting. If
the input signal is siren or trill, the GAIN should be set for maximum volume and the level meter will read
continuously in the red area.

Failure to reduce the gain setting may cause excessive power to be dissipated in the speaker units and
result in failure of the speaker voice coils due to overheating.

Fade operation can easily be performed between microphone and recorder inputs by adjusting the ‘GAIN’
control setting. This operation permits a smooth transition from voice input to tape/playback input and
back again.

CAUTION:

With siren or trill signals, limit full power operation to periods of 15 seconds

ON/OFF to prevent damage to speakers.

3.3.3 Push-to-Test Lamps

These lamps are separately connected to either Section A or Section B of the power amplifier, to provide
independent indications of the status of the separate sections. The lamps should illuminate red when the
POWER switch is selected ON, the voltage and polarity of input power is correct and no protective circuit
has tripped. When pressed with the POWER switch off, the ‘Push-to-Test’ lamps will illuminate to indicate
the presence of DC power at the input power receptacles. Fluctuations in the intensity of either lamp
during operation indicates a high impedance power source or a depleted battery in the relevant section of
the unit.

Section 3 Rev: 1.00 Issue 4 Page 3-2

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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIR BORNE TECHNOLOGY LTD.

PA700 Series High Power Voice Amplifier

SM44 Installation and Operation Manual

3.3.4 Resetting the Protective Circuit

The PA700 Series amplifier is designed with self protecting circuitry to interrupt the operation whenever
unusual conditions exist which might damage the amplifier components.

Unusual conditions might be excessive voltage, voltage spike, speaker short or t emperature rise. Once
the protective circuit is activated, the flow of power is stopped in the affected channel and no further
operation is possible without corrective action. If the trouble was due to a temporary or transitory cause,
operation may be resumed by simply selecting the power switch to OFF and back to ON. If the protective
circuit again shuts the amplifier off, continued operation on that channel is probably impossible without
correcting the problem.

During a mission, should one channel fail, the amplifier can be operated by using the unaffected channel.
The available audio power will be approximately half the normal power. It is advisable to remove the
power cable from the affected channel.

CAUTION:

The transistors of this system are subject to damage when exposed to excessive heat, voltage,

or current for even short periods of time.

The PA700 Series incorporates a protective circuit, which disables the amplifier when safe

operating currents or voltages are exceeded. The protective circuit is adequate in most
instances however, it is also subject to damage when the unit is exposed to extreme or

sustained stresses. Careful monitoring is therefore necessary when operating under unusual

environmental extremes. Precautions should be taken to maintain temperature within

recommended limits. Other damaging conditions are excessive battery charging voltages, short

circuits within the system and transmission of compressed high level music resulting in

continuous high-level power generation.

Operation at high temperature should be limited to short periods. Even at normal temperatures,

operation at continuous full power should be interrupted for 5–10 seconds at 15 second

intervals.

Loudspeakers will overheat with a continuous signal at full power. Voice operation will generate

less heat, and pauses between words will result in a low duty cycle.

Section 3 ends

Section 3 Rev: 1.00 Issue 4 Page 3-3

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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIR BORNE TECHNOLOGY LTD.