Panasonic Easa-Phone VA-208 Installation Manual page 126

HEXPLANATION OF CIRCUIT OPERATION
1. Key telephone with built in speakerphone
1.1 Conversation
Handset is connected to T and R line when HSI is ON.
R38
(I)
(2)
R2f3
DE I
L 1
Incoming
Signal
R33
Receiving circuit
The received voice signal is connected to the receiver via the following path.
T, R terminal + HSI (ON) + DBI (Rectifier) + Sink circuit (Provided to maintain conversation quality by a
constant current supply for various distance conditions to the Central Office Exchange) -+ Tl -+ Q4 (Receiver
amp.) -+ R (Receiver).
Transmitting circuit
The send signal is connected to T and R terminal via the following path.
MIC + 06 (Transmitter amp.) +Tl
+ DBI + HSI (ON) +T, R terminal
NOTE:
When the send voice level is over the specified level, 07 to 09 (The receiver mute circuit) suppresses
the side tone by Q9 (ON).
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