Northern Airborne Technology AA86 - Manual (Page 11)

AA86/87 Stereo Intercom Manual SM48 Rev. 4.00
Page 2-6 Nov 12, 2003
ENG-FORM: 805-0104.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
The speaker-level outputs from conventional car-type stereo sources may also be
connected to the AA86/87 Intercom stereo inputs with the following cautions. First,
some automotive stereos do not permit grounding the negative or return speaker
connection. To overcome this problem, a 0.22uf capacitor (preferably a non-polarized
Mylar or equivalent) may be placed between the negative output lead from each
channel and Intercom ground (see figure 2, below).
S pkr +
S p kr +
S p kr -
S pkr -
Left S pe ak er O utp ut
R 1
R 2
C 1
R 3
R 4
C 2
22
22
4-2 2
4-2 2
0.2 2 µ f
0.2 2 µ f
2 or 6
1 4, 15
3 o r 7
14 , 1 5
S tere o M usic S ou rce A A 86 o r A A 8 7
Inte rcom Inp ut
R ight S pe ak er O utp ut
Figure 2
Second, the speaker level output from a conventional automotive radio is greater than
required for AA86/87 operation (this high level won't damage the AA86/87 - it just
makes stereo volume adjustment awkward). It is therefore recommended that the
speaker outputs be routed through a simple two-resistor ‘L’ attenuator as shown in
Figure 2. These resistors will also function as nominal 'loads' for the speaker outputs as
the AA86/87 stereo inputs are high impedance, e.g. about 4.7K, and are therefore not
intended to, and do not, match or load the automotive radio speaker output.
All resistors may be 22 ohm, 1/2 watt. If additional attenuation is desired/required, the
shunt resistors may be lowered to 10 ohm, 4.7 ohm, or as required.
d)
Stereo Inputs to monaural Headsets
If the AA86/87 Intercom has not been wired for stereo headsets, only one of the two
stereo channels will be heard in the user's monaural headsets (both ears, but still only
one channel). To listen to stereo music sources, without wiring the intercom for stereo
operation, it will be necessary to 'combine' the Left and Right channel outputs from the
stereo music source and to connect this combined, now monaural, music source to the
appropriate Left or Right channel stereo inputs. Where the monaural headsets are wired
to the ‘left channel’ headset outputs, then the combined monaural music source must be
connected to the corresponding ‘left channel’ music inputs.