BENDIXKing KY 96A, Maintenance Manual

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B
KY 96A, KY 97A
Rev 5, Apr 2003 MM 006-05674-0005.dwd Page 4-11
auxiliary inputs to the desired level to be fed to the Mic Intercom input. C1207 filters
high frequency noise and C1210 filters low frequency noise. The output of the sum-
ming amplifier is routed through the main board Mic Intercom input and back through
the main board Comm Audio Out.
Comm Audio In goes through R1214 and is reduced by an inverting amplifier, I1201B,
to prevent distortion through the FET switch, Q1202. The gate of Q1202 is pulled up
by R1219 allowing Q1202 to pass the audio signal. When the TX line is grounded
Q1202 turns off reducing the signal by al least 40 dB.
Q1203, Q1204, Q1205, Q1206, Q1207, and Q1208 form a trans-resistive amplifier
with 18 dB of gain. The feedback resistor, R1237, provides 23 dB of desensitization
to gain changes due to temperature or part variations. CR1202 and CR1203 reduce
crossover distortion. C1219, C1220, C1227, and C1221 reduce the gain above the
audio passband to prevent oscillation. The audio drivers, Q1207 and Q1208, provide
a minimum of 4 watts for 13.75 V units and 8 watts for 27.5 V units into a 4 ohm load.
The output is fused by F1201 to protect the drivers. R1238 is in parallel with the fuse
to provide residual audio in case the fuse blows.