Northern Airborne Technology AA23 - Manual (Page 10)

AA23 Speaker Amplifier Manual SM23 Rev. 4.00
An internal trimpot is provided to permit level adjustment of the over-all system. As
shipped, range remains in both directions, up and down.
A set of uncommitted relay contacts (2 A rating) is provided that is closed when the unit
receives a mute command (key ground input). This can be used for external switching.
Fully muted (no output) and partially muted outputs are available to provide a choice of
enabled or disabled speaker sidetone. The muting circuit inserts a 44
Ω resistor in
series with the load, to reduce the output level.
Two external, unrelated key inputs can mute the AA23, and both provide a flow-through
key output to other systems. This permits two users in a close cockpit installation to
mute each other's speakers to prevent feedback, and provides outputs to the balance of
the audio system for TX keying.
The headset input places a greater than 1.8 k
Ω load on the existing headset driver
system, which represents a negligible load. It is a fully floating input, and will not
introduce any ground loop interference unless grounded via the user interconnect. This
line is meant for signals of typically +17 dBm to +20 dBm (50 mW/600
Ω).
The 600
Ω line input can be used with lower level sources to provide a speaker buffer
as needed. Input sources can be music, radio feeds (via a pad) or other sources. Note
that this connection is the direct input to the AA23 transformer, and is isolated from the
headset input only by a simple resistive pad. Signals injected here may appear back at
the headset input, and cause problems if isolation was intended.
The mic input accepts a ‘carbon-equivalent’ unit, and has internal excitation from the
AA23. The input is floating, and must have a ground at the input low connection to
excite the microphone. This is normally provided by any NAT audio system if used to
provide the mic input (PA position).
1.4 Specifications
1.4.1 Electrical Specifications
Input Power +22 to 32 Vdc.
Supply Current 1.0 A max. (at full output into 3.2 Ω).
0.3 to 0.5 A (typical)
Input Levels
600 Ω input 0.45 Vrms (-5 dBm) at 1 kHz.
H/S Input 7.70 Vrms (+20 dBm) at 1 kHz.
Mic Input 0.25 Vrms at 1 kHz.
Page 1-2 Nov 21, 2003
ENG-FORM: 800-0106.DOT
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