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5. Muting when the unit is switched from STOp
to REC is basically the same as that described
in Paragraphs 1 to 3. Pin 16 of ICsor will be-
come H level, and hence current will flow
through Rszz to Qsos. When Qsos becomes
conductive, Qsoo, Qsoz and Qzor will be tumed
off, and thus the muting condition will be re-
moved from the recording amplifier.
Bias Muting Circuit
During recording, the bias signal is sometimes
recorded due to the increase in the relative speed
of the tape and head during the on/off switching
of the PAUSE or release of the recording controls.
The recorded bias signal can be heard as a ,,click"
noise when the tape is played back at its fixed
speed; the purpose of this circuit is to suppress
this noise.
1. During REC/PLAY operation (when the REC
and PLAY switches are turned on simultaneous-
ly), the No. 16 pin on ICsor reaches H level, and
because the Q:ot receives bias and comes on.
the oscillator circuit operates.
cT-Fs'E'Cl
2. When the PAUSE switch is turned on, the No.
19 pin of ICsol reaches H level, and the bias
comes on through the Dsoz -
Rszo -
Rsro
route to send bias current to esoe.
3. With Qsoe on, Qsro is also tumed on, and +B
takes the Dsrz -
Rror route to tum on eror.
4. With Qror turned on, Crot and Rror follow a
fixed time constant and turn on eroz by reduc-
ing the emmiter voltage.
5. When Qroz comes on, the bias current flows
through the condenser and is grounded. Bias
current is supplied to neither the base of etoe ,
Qsoz nor to the record head.
6. When the PAUSE switch is set to OFF, the
PAUSE operation is halted and recording re-
sumes. However, even if the No. 19 pin on
ICsor reaches L level, since the discharge time
for Cro: (determined by the Cros and R:os
time constants) only turns on eroz, there is
no bias supplied to the record head.
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F i g . 7 - 1 1 B i a s m u t i n g c i r c u i t
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