Teac TASCAM 32 - Page 71

1-16-2. Bias and Record Control Circuit
See Figs. 1-15(A) and 1-15(B).
1. As previously described, when the unit is in
REC mode, REC SIG (+24 V) is produced at
Q525 collector. This signal is applied to the
FUNCTION switches. If any one (or more) of
the switches (for example F) is set to ON or
into the record mode: (1) the common ter-
dIN2
TO OUTPUT AMPL.
QO CH
SYNC HEAD
4"
~~ 7
"Ota
REC AMPL.
ERASE HEAD
xX
0 O-— +15V
l ] | u301
MASTER BIAS OSC
—I5V
REC SIG. (+24V)
(FROM Q525,Q579)
t
be ee a ee
minal of Fa is connected to a +24 V line and
voltage is supplied to D109, D117 and D115.
Thus, Q108, Q109 and Q120 go on, and
Q118, Q119 also go on. (2) The Fb common
terminal is grounded, causing REC LED
indicator to light continuously as described in
section 1-15 ‘‘Display Circuit’’.
Ql20
RIQi DIIS
RI97 RI94 cas RI92
FUNCTION SW
oT ONE ee)
O \S INDICATED
©)
Fa
1
REC MODE (TO R51!)
CHANNEL INDICATER
Fig. 1-15(A). Bias and Record Control Circuit
72
2
When
Q109
is
turned
on,
FET
switching
transistor
Q110
is
on
and
part
of
the
record-
ing
signal
is
applied
to
the
OUTPUT
amplifier,
allowing
recording
to
be
monitored.
When
Q120
goes
on,
REC
relay
K103
is
energized,
the
record
head
is
switched
to
the
record
amplifier,
and
the
cold
side
of
the
erase
head
is
grounded.
Thus
recording
is
made.
On
the
other
hand,
when
Q119
goes
on,
bias
oscillator
amplifier
unit
U103
starts
to
amplify
the
bias
signal
supplied
from
master
bias
oscillator
U301
and
the
amplified
output
is
supplied
to
both
the
record
and
erase
heads.
OUT SELECT SW —— SYNC
REC ON
(INCLUDING FUNCTION ON)
REC SIG
OUTPUT SYNC
REC RELAY
BIAS OSC
3.
The
on
and
off
switching
timings
for
all
above
circuits
(the
bias
switching
circuit
comprising
Q118
&
QO119,
the
REC
relay
switching
circuits
comprising
Q120,
and
the
OUTPUT
(SYNC
—
INPUT)
switching
circuits
compris-
ing
Q108
&
Q109)
are
suitably
fixed
so
that
transient
noise
has
no
undesirable
influence
on
recorded
sound
quality.
The
switching
timings
(delay
time
periods)
of
the
circuits
depend
on
the
values
of
C132,C135
and
C119,
respectively.
For
details
on
the
relationship
between
these,
refer
to
Fig.
1-15(B).
REC: OFF
(INCLUDING FUNCTION OFF)
Fig.
1-15
(B).
Record
Circuit
Switching
Timing
Diagram
73