KX-TEB308CA, KX-TE82460X, KX-TE82493X, KX-A227X - Panasonic PBX Service Manual (repair manual). Page 14

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This circuit consists of bidirectional amplifier function for communication between the extensions and COL, returns loss com-
pensation for conference, shunt function and mute function.
(Composition)
For transmitting signals from the extensions to COL, this circuit consists of R34, R35, R26, R27, R18, R29, C14, C15, C10, C16
and the operational amplifier (IC1).
For transmitting signals from the COL to extensions, this circuit consists of R24, R25, R31, R28, R37, R30, C12, C13, C17, C18,
and the operational amplifier (IC1).
COL side-tone suppression circuit which includes a balanced network BN1 consists of R22 R23, C11 and R16, R17, R20, R21.
EXT side-tone suppression circuit which includes a balanced network BN2 consists of R41, R42 and R40, R43, R38, R39.
Also extension side-tone suppression circuit which includes a balanced network BN3 consists of R45, R46 for supplementing
side-tone suppression during the conference communication.
The analog switch (IC2) is used for the following:
(1) Conference (Pin 6, 8 and 9)
(2) Shunt (Pin 12, 10 and 11)
(3) Mute (Pin 13, 1 and 2)