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Equalizer/microphone amp. (FiS. 1 1)
The microphone amp section of the PA4001 is
used. Its input is a differential amplifier, and its
output is an emitter follower type. When recording,
this circuit is used as a flat frequency response
microphone amp by switching the NFB circuit. At
playback, it is used as a playback equalizer amp by
making the NFB circuit a time constant circuit.
The playback equalizer amp is switched between
CrOz, Fe-Cr and STD. At CrOz, Fe-Cr, a CR series
circuit is inserted at the output side of the
equalizer amp by a transistor switch.
When a cassette half having a chrome tape
detector hole is loaded (CrOz tape detector switch
Ss at the HOLE position), or the EQ switch S+ is set
to the Fe-Cr, CrOz position, +B is supplied through
the route Dzoe or Dzos > F.zzt > 3tt3 r Qror .
Since Qror is tumed ON by cancelling of -B, the
amp is made a CrOz (Fe-Cr) equalizer amp (time
constant ?Opsec at the high range) by Caoa and
R a r r .
When a cassette half not having a chrome tape
detector hole (Ss at the NO HOLE position) and
S+ is set to the STD position, +B is not supplied
to Qror and Qror is tumed OFF by -B
(time
constant 120psec at the high range).
Recording bias switching circuit (Fig. 12)
The recording bias is switched between CrOu
and Fe-Cr, and STD. The bias current is switched
by changing the oscillation width by changing the
bias oscillator supply voltage. The bias current
can be varied fuom -LiVo Lo +lo7o for CrOz and
from -2O7o to +157o for Fe-Cr and STD, by
adjusting the bias fine-adjustment semifixed resistor
VRzoz. At the center click position, the reference
bias OV" of the set is indicated
at the THIRD
METER (BIAS meter).
When a cassette half without
chrome tape
detector hole is loaded (CrOz detector switch Ss at
the NO HOLE position), at recording power is
supplied to the oscillator circuit through the route
Rzzr and Ss'Dzos > Rurs'VRzoz. Since theseries
with Rzzs when a cassete half vrith detector hole is
loaded (Ss at the HOLE position), the voltage
supplied to the oscillator circuit becomes high.
When VRzoz is at the center click position, the
CrO2 recording bias becomes approximately 20Vo
to 30Vo deeper than for STD/Fe-Cr.
The recording bias is indicated on the bias meter
by setting the THIRD METER switch Sro to the
BIAS position. VRzos is for "0" adjustment of the
STD/Fe-Cr bias indication, and VRzoq is for "0"
adjustment of the CrOz bias indication. Quor acts
as a switching transistor which mutes the THIRD
METER when the REC/PB switch Sz is set to the
PB position and the MUTING switch Sz is set to
the ON position.
?
S T D
RJI]
CJoB
0 lot
+ 8 1
r o
s ?
l l t L
REC/PB head
Sr: REC/PB switch
Ss : CrO2 lape sense switch
S r o : T H I R D M E T E R s w i l c h
i | | t h - r
r N p J r v R
#
r,r're f,
Mlc llvl
Equàr,ze,/
r,4rc
f
I REC mrc.ophone
amp
' r c -
P R
S , .
R E C / P B r w i r c h
S . :
E Q s w i r c h
St:
CrO, taæ sense switch
5 6
I N P U T s w i t c h
5 z
F i g . 1 1 E q u a l i z e r / m i c r o p h o n e a m p c i r c u i t
H O L E
rr i:#*'riib-
Fig. 12 Recording bias switching circuit
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