Muting Circuit; When Power Switch Is Pressed On; When The Power Switch Is Pressed Off - Pioneer CT-F950 Service Manual

7 . 7 M U T I N G C I R C U I T
Muting When the Power Switch is Pressed On and
off
This circuit is designed to eliminate noise (e.g.
click noise) 'vhen the POWER switch is pressed
on or off (Fig. 7-9).
r When Power Switch is Pressed On
1. When the POWER switch is pressed on, the
emitter voltage of Qoor will immediately rise to
approximately 5.6V. Because current does not
flow into Coor, the voltage across its terminals
will be 0V. Consequently, in the Schmitt
trigger comprising Qooz and Qcor, Qeor will be
turned off and Qeor will be turned on. Also,
Qsoe will be tumed off and Qsos will be turned
on, and thus the 5.6V source will produce a
current flow through Dcor into Qroz and Qroe.
As a result, Qroz and Qror will become con-
ductive, thus short circuiting the LINE OUTPUT.
2. Meanwhile, Ceoz and Ce rs rapidly charge up.
When Cooa charges up, the base potential of
Qoos will become -6V, and hence Qoor will
be turned off.
Consequently, the voltage across the terminals
CT-F9SCl
of ZDoor will become approximately 6V. Thi
voltage will cause current to flow through Rc r:
and charge up Coor. When the voltage acros
Ce or reaches the reversing level of the mutinl
circuit (Approximately
4 seconds after thr
POWER switch has been pressed on), Qooz wil
turn on and Qeor will tum off. Because Qeor
will be turned on, and Qeos, Qroz and Qloe
will be turned off, the LINE OUTPUT mutinl
condition will be removed.
r When the Power Swibh is Pressed Off
1. When the power switch is pressed off, thr
charges stored on Coor and Cors will rapidl5
decay. Consequently, the charge on Coor wil
flow through Door and Roor into the base o
Qa r c.
When Quoe becomes conductive, tht
charge on Coor will rapidly decay.
2. Consequently, Qe oz will now be turned on, an€
Qooe turned off. Qcoe will be turned off, anc
Qoos, Qroz and Qlor turned on, hence tht
LINE
OUTPUT will be muted.
After the
POWER switch has been pressed off, the power
supply for the unit will be charged on Cooz.
Fig. 7-9 M u t i n g c i r c u i t 1