NAT 437 audio amplifier Installation and operation manual
Model 437 Audio Control Amplifier is a remotely controlled intercom/audio amplifier for aircraft with two cockpit audio stations. It switches up to 14 receivers, 4 sidetone inputs and an interphone. Headphone and selected speaker outputs are isolated with a cockpit voice recorder output providing summation of headphone, speaker and microphone audio. Microphone audio is recorded on the CVR at all times.
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Installation and Operation Manual
Model 437
Audio Control Amplifier
SM437
ISSUE 2.00
Northern Airborne Technology Ltd.
1925 Kirschner Road
Kelowna, BC, Canada.
V1Y 4N7
Telephone (250) 763-2232
Facsimile (250) 762-3374
Issued on the authority of Northern Airborne Technology Ltd.
Copyright 2005
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Northern Airborne Technology Ltd. has acquired the assets of dB Systems Inc., and has reissued this manual in full NAT format.
Northern Airborne Technology Ltd. will be responsible for all future amendments and revisions.
Installation and Operation Manual
ENG-FORM: 820-0114.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Page ii
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Table of Contents
Section Title
1. Description
1.1 Introduction
1.3
1.4
1.4.1
Design Features
Specifications
Electrical Specifications
1.4.4
1.5
Product Approval
Model 437 Nomenclature
2. Installation
2.1 Introduction
2.2 Unpacking and Inspection
2.2.1 Warranty
2.3
2.4
2.4.1
2.4.2
Continued Airworthiness
Installation Procedures
Warnings
Cautions
2.4.3
2.4.4
2.4.5
2.4.6
2.4.7
2.4.8
2.4.9
2.5
2.6
2.7
Cabling and Wiring
Mechanical Installation
Electrical Installation
Pin Identification
Modes of Operation
Interconnect Information
Post-Installation Checks
Adjustments
Accessories Required But Not Supplied
Installation Drawings
3. Operation
3.1 Introduction
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Installation and Operation Manual
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Section 1 Description
1.1 Introduction
Information in this section consists of product description, design features and specifications for the
Model 437 Audio Control Amplifier. Information on the 437-001 and 437-003 is included in this manual.
For information on other derivative products, please contact Product Support at NAT Ltd.
Review all notes, warnings and cautions.
1.2 Product Description
The Model 437 Audio Control Amplifier is a remotely controlled intercom/audio amplifier, which operates upon command from switches and potentiometers in the cockpit. The Model 437 is capable of switching up to 14 receivers, 4 sidetone inputs and an interphone line. Five unswitched and unmuted inputs are also provided to accommodate an aural warning input and 4 auxiliary inputs. Headphone and Selected
Speaker outputs are isolated and a Cockpit Voice Recorder output provides summation of headphone, speaker and microphone audio. Microphone audio is recorded on the Cockpit Voice Recorder at all times with the Model 437 (i.e. the microphone to Cockpit Voice Recorder audio channel is unswitched and unmuted).
1.3 Design Features
Headphone and Speaker channels are powered from separate 28 Vdc power inputs so that one channel will still operate if the other fails.
Receivers and operating modes are electronically switched. The electronic switches in the Model 437 are enabled by ground signals, supplied by manual switches in the cockpit.
Selective voice or code filtering is provided on four of the receiver audio inputs, intended for ADF and
NAV audio. The filter function is electronically controlled by ground signals from the cockpit Voice-Off-
Range switch.
A voice-activated switch is incorporated in series with the microphone input to reduce interphone noise.
This feature allows Hot Interphone operation without ambient noise being coupled into the amplifier when the pilot is not talking. The threshold of voice activation may be adjusted by a screwdriver adjustment through an access hole in the Model 437 cover (marked THLD). It is factory set at 100 millivolts and adjustable from 15 to 150 mV. The microphone to Cockpit Voice Recorder audio channel does not employ the Voice Activated Switch circuitry.
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Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Specifications 1.4
1.4.1 Electrical Specifications
The Model 437 is intended for aircraft with two cockpit audio stations. Two Model 437 amplifiers are installed, one for each audio station. The receiver outputs are connected to both Model 437 receiver inputs. The receiver input impedance of the Model 437 is 1000 ohms, so when the two amplifiers are installed, the receiver sees 500 ohms. Input specifications are expressed in Vrms, rather than milliwatts, to avoid misunderstanding.
Inputs
COMM 4 dual audio inputs for receiver and sidetone. Receiver input level is 7.75 Vrms and Sidetone is 3.87 Vrms, both switched simultaneously.
RCVR
FLTR
6 single, switched audio inputs for MKR, DME, TACAN, etc.
Input level is 7.75 Vrms.
4 single, switched audio inputs for NAV, ADF, etc. 7.75 Vrms inputs have selective filtering, switched by the Voice-Off-Range switch.
AUX
AW
Voice: 1020 ± 5 Hz, 30 dB, 100 Hz notch
Range: 1020 ± 5 Hz Ident Tone emphasis
4 unswitched and unmuted auxiliary inputs, factory set to accommodate 3.87 Vrms. The AUX screwdriver adjustment may be changed for higher or lower levels.
This is an unswitched and unmuted input compatible with the aural warning output of the Model 207 or equivalent, which provides Stall, Altitude Alert, Landing Gear, Take-Off-Out-Of-
Trim, Decision Height and Autopilot Disconnect warning tones.
Input varies with tone, approximately 4 VPP into 15K.
MIC
Headphone Volume
Speaker Volume
Sidetone Volume
Outputs
Headphone
The microphone input, used for interphone mode, supplies bias and is compatible with carbon and amplified dynamic microphones. Voice activated within 1.5 milliseconds by a circuit that provides 30dB minimum attenuation within 2 seconds after speech. 15-150 mV threshold range.
Controls level of all audio inputs except sidetone, auxiliary and aural warning. Volume control range is 30dB (minimum) controlled by a 10,000-ohm ½ watt linear pot. Maximum volume is with maximum resistance.
Same as Headphone Volume specification.
Same as Headphone Volume specification.
The headphone output will deliver up to 80 milliwatts into 600 ohms continuously. Above that level, peaks will be clipped but it will not damage the amplifier. Rated & Continuous power specification are the same.
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Voice Recorder
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
This output will deliver 1 milliwatt into 600 ohms continuously.
Rated and continuous power ratings are the same.
Speaker The speaker amplifier is designed for speech signals and has both a rated power and a Continuous Power specification. The continuous rating is the power the amplifier can continuously deliver with a sine wave. The Rated Power specification is the peak power it can deliver without clipping. Bench testing and adjustment may require brief periods of sine wave operation above the continuous rating, those periods should be limited to 1 minute to prevent amplifier damage.
Frequency Response
Harmonic Distortion
Load
4 ohm
8 ohm
Rated Power
10 Watts
8 Watts
Flat within 3 dB from 350 Hz to 6000 Hz.
Less than 3 percent distortion, all outputs.
Continuous Power
1 Watt
0.8 Watts
Power Supply 28 Vdc, 1 Ampere maximum.
Isolation Between Channels 60 dB Minimum
Output Noise Greater than 60 dB below rated, all outputs.
Height
Depth
Width
Weight
1.93" (49.02 mm) max
4.93" (125.22 mm) max including flanges
7.30" (186.18 mm) max including flanges
1.45 lbs (685 g)
Temperature -55 o
C to +70 o
C
Humidity 95% 48 hours
Shock 6g for 11 ms in all axes
Qualification of the Model 437 Audio Control Amplifier was completed in accordance with
RTCA DO-160A Environmental Categories: F2A/JLO/XXXXXXX/BZ/AAA
1.4.4 Product Approval
FAA: TSO-C50c (RTCA/DO-170 Class Ib, RTCA/DO-160A)
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Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
1.5 Model 437 Nomenclature
The Model 437 derivatives are listed below:
Model 437-001
Same as Model 437 base except that it allows increased Cockpit
Voice Recorder levels for use on Beech 1900 aircraft with low
Comm and Receiver output levels.
Model 437-002 Same as Model 437 base except that it allows increased Cockpit
Voice Recorder levels for use on Beech 1900 aircraft. Contact
Product Support at NAT Ltd for further information.
Model 437-003 Same as Model 437 base except that it allows increased Cockpit
Voice Recorder levels to improve reception of audio signals by solid state CVR’s.
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Model 437 Audio Control Amplifier
SM437 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 Model 437 Audio Control 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
- 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 warranty card is not returned shall be warranted from date of manufacture.
2.3 Continued Airworthiness
Maintenance of the Model 437 Audio Control Amplifier is ‘on condition’ only. Periodic maintenance of this product is not required.
2.4 Installation Procedures
2.4.1 Warnings
WARNING:
High volume settings can cause hearing damage.
Set the headset volume control to the minimum volume setting prior to conducting tests, and slowly increase the headset volume to a comfortable listening level.
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2.4.2 Cautions
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
CAUTION:
In all installations, use shielded cable exactly as shown, and ground only as indicated. Significant problems may result from not following these guidelines.
Failure to follow the installation and wiring instructions provided in this manual for power and ground connections, including the rating of the circuit breaker, may lead to damage in the power input circuitry of the unit.
2.4.3 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 solder sleeves (for 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. Note that the hood is a "clamshell" hood, and is installed after the wiring is complete.
Maintain wire segregation and route wiring in accordance with the original aircraft manufacturers
Maintenance Instructions.
All wiring shall be 24-26 AWG, except speaker amplifier lines (pins 9-12 and 29-31 of P40), which shall be 20-22 AWG. Reference the Interconnect drawing for additional specifications. Check 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.
2.4.4 Mechanical Installation
The Model 437 may be mounted in any position. No shock or vibration isolators are required.
The amplifier may be mounted to metal or plastic surfaces but it is necessary to ground the case to the aircraft structure. When mounting to a plastic surface, a grounding strap must be used. The case is finished with an electrically conductive film, so it is not necessary to remove the film with a bonding brush.
It is recommended that the amplifier be installed so that the screwdriver adjustments are easily accessible.
2.4.5 Electrical Installation
Connections to the Model 437 are made through two 'D' subminiature connectors. See section 2.5 for information on the connectors and Installation kits.
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Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Pin Identification 2.4.6
2.4.6.1 P40 Pin Identification
The table below shows the pin identifications for the 37-pin connector (P40):
PIN DESCRIPTION
1 No Connection
2 XMT PTT
3 MIC HI
4 HDPH HI
5 HDPH 28VDC
6 HDPH LO
7 HDPH PWR GND
8 CVR HI
10
11
12
13
14
15
16
17
18
SPKR 28VDC
SPKR HI
SPKR PWR GND
AURAL WARN LO
AUX 1 LO
AUX 2 LO
AUX 3 LO
AUX 4 LO
AUX 4 HI
33
34
35
36
29
30
31
32
37
PIN DESCRIPTION
20 INPH AUDIO
21 SIDETONE ENABLE
22 HDPH VOLUME
23 INPH KEY
24 MIC LO
25 INPH TO SPKR SW
26 HDPH PWR GND
27 CVR LO
28
AUDIO COMMON (SPARE)
SPKR LO
SPKR PWR GND
SPKR PWR GND
AURAL WARN HI
SPKR SW
SPKR VOLUME
AUX 1 HI
AUX 2 HI
AUX 3 HI
2.4.6.2 P50 Pin Identification
The table below shows the pin identifications for the 50-pin connector (P50):
PIN DESCRIPTION PIN DESCRIPTION PIN DESCRIPTION
1 NAV 2 HI
2 ADF 2 HI
3 MKR 1 HI
4 MKR 2 HI
5 MKR 1 SW
6 DME 2 SW
7 MKR 2 SW
8 COMM 1 SW
9 COMM 2 SW
10 COMM 3 SW
11 COMM 4 SW
12 NAV 1 LO
13
COMM 1 SIDETONE
14
COMM 2 HI
15
COMM 2 SIDETONE
16
COMM 3 HI
17
COMM 3 SIDETONE
18
19
20
21
22
23
24
25
26
27
28
29
30
31
NAV 1 HI
DME 1 HI
DME 2 HI
DME 1 SW
NAV 2 LO
ADF 2 LO
MKR 1 LO
MKR 2 LO
ADF 1 LO
COMM 3 LO
COMM 2 LO
COMM 1 LO
COMM 1 HI
SPARE 2 SW
32 SPARE 2 HI
33
COMM 4 SIDETONE
34 ADF 1 HI
35 NAV 2 SW
36 NAV 1 SW
37 ADF 1 SW
38 ADF 2 SW
39 IDENT SW
40 VOICE SW
41
42
43
44
45
46
47
48
49
50
DME 1 LO
DME 2 LO
COMM 4 LO
SPARE 2 LO
SPARE 1 LO
No connection
SIDETONE VOLUME
SPARE 1 SW
SPARE 1 HI
COMM 4 HI
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SM437 Installation and Operation Manual
Modes of Operation 2.4.7
The Model 437 can be configured for several different modes of operation by applying a ground signal to the appropriate connector pin (see below):
Pin No. Identification Function
P50-40 Voice Switch
P50-39 Ident Switch
Enables notch filter to reject Ident Tone on NAV and ADF audio inputs.
Enables bandpass filter to emphasize Ident Tone.
P40-33 Speaker Switch Connects selected audio to the Cockpit Speaker.
P40-23 INPH Key Connects microphone to the interphone line if XMT PTT is not selected.
P40-25 INPH to SPKR Connects Interphone Audio to Cockpit Speaker.
Opens the microphone to interphone circuit and mutes both headphone and speaker audio. Mute level is adjustable.
SPKR Switch is on).
The control switches shown will switch low-current loads and should have a DC rating of 28 Vdc. Typical switches for this application include Alco MTA series.
A single pole, three-position switch is recommended for the Voice-Off-Range switch. Applying a ground signal to both pins P50-39 (Ident) and P50-40 (Voice) simultaneously will result in improper filter operation.
2.4.8 Interconnect Information
Continued on next page
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Interconnect (Continued)
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Continued on next page
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Interconnect (Continued)
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Continued on next page
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Interconnect (Continued)
Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
2.4.9 Post-Installation Checks
If any preset requires adjustment, be sure this is carried out before the aircraft leaves, and that the unit and its mating connector are secured before departure. Make all required log book entries, electrical load, weight and balance amendments and other paperwork as required by your local regulatory agency.
2.4.9.1 Voltage/Resistance Checks
Do not attach the Model 437 until the following conditions are met.
Check the following: b) Check for continuity to ground (less than 0.5
Ω). c)
Confirm that P40 pins <2> <21> <23> <25> and <33> are grounded (less than 0.5
Ω) when the appropriate switches are closed. d)
Confirm that P50 pins <8> <9> <10> <11> <5> <7> <21> <6> <48> <31> <36> <35> <37> <39> and
<40> are grounded (less than 0.5
Ω) when any appropriate switches are closed.
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SM437 Installation and Operation Manual
Power On Checks 2.4.9.2
WARNING:
High volume settings can cause hearing damage.
Set the headset volume control to the minimum volume setting prior to conducting audio tests, and slowly increase the headset volume to a
comfortable listening level.
Power up the aircraft’s systems and confirm normal operation of all functions of the Model 437.
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.
2.5 Adjustments
SPKR
|
FLTR
|
AUX
|
SDTN
|
THLD
|
MUTE
|
There are six adjustment potentiometers that are accessible through the cover of the Model 437 amplifier (see left). They are intended for trimming the relative audio levels to suit individual operator needs.
The speaker (SPKR), auxiliary (AUX), threshold (THLD), filter (FLTR), sidetone (SDTN) and mute (MUTE) volume control pots are located on the side of the unit.
SPKR: varies speaker audio level (all signals)
AUX: varies level of all four auxiliary inputs to speaker and headphones
THLD: varies threshold of voice activating the interphone mic input
FLTR: varies level of NAV/ADF audio when passed through Voice or Range filter
SDTN: varies level of sidetone to the cockpit speaker
MUTE: varies level of speaker muting during transmit (XMT PTT depressed)
The potentiometers are linear taper, multiple turn (20 turns nominal), and provide full volume when rotated fully clockwise (cw). These potentiometers have been factory set to comply with the requirements of the unit Test procedures.
It is important to refer to Table 1 in the Acceptance Test Procedure (see Section 5 of the SM437
Maintenance Manual) if these settings are changed. It is necessary to make the adjustments in the order shown in Table 1 to prevent inadvertently setting an incorrect level.
Example: If the MUTE (R53) level is set for .63 Vrms of DME audio into the cockpit speaker during transmit and later the SPKR (R12) pit is turned up, the mute level will also increase. When making any adjustment it is important to understand its relationship to the levels established by the other pots.
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Accessories Required But Not Supplied 2.6
To complete the installation, the Model 437 requires two crimp Installation kits, D37SL-IKC and D50SL-IKC.
The kits consist of the following:
NAT Part #: D37SL-IKC
Quantity Description NAT Part #
1
37
1*
1*
1
NAT Part #: D50SL-IKC
D-min 37 Socket Housing
MS Crimp Socket
Jack Screw Set
Lock Clip Set
37 Pin Connector Hood
20-21-037
20-26-901
20-27-002
20-27-004
20-29-038
Quantity Description NAT Part #
1
50
1*
1*
D-min 50 Socket Housing
MS Crimp Socket
Jack Screw Set
Lock Clip Set
1 50 Pin Connector Hood
* Use as required
20-21-050
20-26-901
20-27-002
20-27-004
20-29-051
2.7 Installation Drawings
TYPE
437
437\437 1.61 Audio Control Amplifier Outline - Assembly
Section 2 ends following the above documents
SERIAL No.
All
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Model 437 Audio Control Amplifier
SM437 Installation and Operation Manual
Section 3 Operation
3.1 Introduction
Information in this section consists of functional and operational procedures for the Model 437 Audio
Control Amplifier.
3.2 General Information
The Model 437 Audio Control Amplifier is a remotely controlled intercom/audio amplifier, which operates upon command from switches and potentiometers in the cockpit. The Model 437 is capable of switching up to 14 receivers, 4 sidetone inputs and an interphone line. Five unswitched and unmuted inputs are also provided to accommodate an aural warning input and 4 auxiliary inputs. Headphone and selected speaker outputs are isolated and a cockpit voice recorder (CVR) output is the summation of headphone, speaker and microphone audio. Microphone audio is recorded on the CVR at all times (i.e. the microphone to CVR audio channel is unswitched and unmuted).
3.3 Controls and Indicators
The Model 437 Audio Control Amplifier has no operator accessible controls.
At installation, the Model 437 is provided with several external switches that can be used to modify the operational modes of the unit (see below):
Identification Function
Voice Switch
Ident Switch
Enables notch filter to reject Ident Tone on NAV and ADF audio inputs.
Enables bandpass filter to emphasize Ident Tone.
Speaker Switch Connects selected audio to the Cockpit Speaker.
INPH Key Connects microphone to the interphone line if XMT PTT is not selected.
INPH to SPKR Connects Interphone Audio to Cockpit Speaker.
XMT PTT Opens the microphone to interphone circuit and mutes both headphone and speaker audio. Mute level is adjustable.
Sidetone Enable Connects selected Comm Sidetone to the Headphones and Speaker (if SPKR Switch is on).
During installation, it may be determined that internal level adjustments are required. Qualified personnel only shall complete internal level adjustments.
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Key features
- Remotely controlled
- Intercom/audio amplifier
- Switches 14 receivers
- Headphone and speaker outputs
- Cockpit voice recorder output
- Voice-activated switch
- Selective audio filtering
- Separate power inputs
- Electronic switches
- Adjustable audio levels