Yamaha CT-7000 Service Manual page 15

MULTIPLEX DEMODULATOR CIRCUIT
This circuit double tunes the composite signal by a
switching method, thus separating out the left and
right channel audio signals.
COMPOSITE
SIGNAL (INPUT)
Operation
The composite signal entering at
and becomes output due to the low impedance of
the Tr2 emitter-follower circuit.
Also, via the 12 and b terminals a 38kHz square wave
is constantly received from the PLL circuit. At terminal
14
a minus potential is received only when the signal
is in stereo.
Therefore, when a stereo signal is received Tr3 comes
on. Tr4 and Tr5 repeat seesaw on-off motions at the
38kHz frequency, which drives Tr6 and Tr7. When
Tr4 is on, Tr6 comes on
I! is amplified by Trl
(at the same time Tr5 is
off, switching Tr7 off). When Tr4 turns off, it switches
off Tr6 (at this time Tr5 is on and thus so
In this way the grounded-open movement is repeated
0 CV
between points and at the 38kHz rate, permitting
the right and left audio signals to be obtained from
the composite signal. One part of the audio signal is
fed back through terminal
tion characteristics. In addition, when a monophonic
signal is being received, Tr3 shuts off, and this turns
off Tr4, Tr5, Tr6 and Tr7, so that the audio signal
obtained at terminals Lo
SIGNAL
Fig. 8
is Tr7).
h for more p erfect separa­
Ro
and are mowphonic.
CT-7000
13