Panasonic KX-FT72BR-G Service Manual page 130

KX-FT72BR-G
5.8.5. LINE AMPLIFIER AND SIDE TONE CIRCUITS
1. Circuit Operation
The reception signal received as output from line transformer T2 is given as input to C23, R33 and IC2 pin (6).
Then it is input to the reception system at an amplifier gain of 5.9 dB from pin (6).
The transmission signal is input from CN1 pin (11), and output to the TEL line through C30, R31 and T2. Without a side tone
circuit, the transmission signal would return to the reception amplifier via C30 and R31. Here, the signal output from CN1 pin
(11) passes through C30, C36 and R39 and enters the amplifier IC2 pin (5). This is used to cancel the return portion of the
transmission signal. This is the side tone circuit.
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