AA21-401 Remote Cabin PA System
SM34 Installation and Operation Manual Supplement
SM Supplement Rev: 1.01
Mar 23, 2009
Page 1
ENG-FORM: 810-0111.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
This supplement contains installation and operation information that is unique to the AA21-401 Remote
Mount Cabin PA system. Installation and operation information common to the AA21-400 base unit can
be found in the
SM34
Installation and Operation Manual.
Section 1 Description
The AA21-401 Remote Mount Cabin PA system is designed to provide centralized control for an aircraft’s
internal and external PA systems. The unit is a remote mounted box designed to interface to external
user controls. All power, audio and keylines are interfaced to existing aircraft audio systems through a
second external connector.
1.1 Performance/Function
The AA21-401 provides an internal PA and/or drive circuitry for external PA system(s) installed in an
aircraft. The integrated 20 W speaker driver circuit is designed to drive one 8 Ohm speaker arrangement
for internal paging. The AA21 also provides a low-level audio signal output to drive remote mounted
power amplifiers. It may be configured to drive either the PA110/220 series amplifiers, or the PA250/700
series amplifiers. The AA21 provides wail and yelp siren audio on the low level output when selected via
the external user controls.
A ‘+3 dB’ function allows the output level of the system to be varied by 3 dB. When the input control line
is grounded, the output is reduced by approx 3 dB. Removing the ground returns the system to full
output.
Thermal protection is designed into the intermediate and final stage amplifiers to protect the unit during
very hot or extended high power operating conditions.
Current protection is provided using one fuse on the +28 Vdc power input and a second fuse on the
switched power output.
Connections are provided to interface four front panel switches allowing selection of the various
operational modes of the AA21; POWER (Power On/Off), INT/EXT (Internal SPKR on/External PA on),
YELP/OFF/WAIL (Yelp siren on/Siren off/Wail siren on), RADIO/PA (radio [receive] input enabled/PA Mic
input enabled). Interface to a front panel potentiometer is included, to provide volume level control of the
selected output. The interface can also drive an annunciator to provide Power On indication.
1.2 Electrical
Specifications
The AA21-401 is identical to the AA21-400, with the following additions:
Remote Control Connector
Input Signals
+28 VDC Switched
External Speaker Select
Active low, 5 mA max
Internal Speaker Select
Active low, 10 mA max
PA Select
Active low, 5 mA max
Radio Select
Active low, 5 mA max
Rx Disable
Active low, 5 mA max
23-31-90
The document reference is online, please check the correspondence between the online documentation and the printed version.