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Fostex G16 - Page 30

Fostex G16
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divided
to
1/4
by
UI
2.
The
variable
oscillator
circuit
uses
the
timer
IC
555
(U9)
and
frequency
varied
by
the
pitch
control
pot.
The
oscillating
center
frequency
is
9.6KHz.
When
the
PITCH
CONT
SW
is
switched
on,
pin
lof
Ull
goes
to
L
and
the
output
of
U9
is
applied
to
pin
1
of
UI
2.
When
the
switch
is
off,
pin
2
of
UI
1
is
at
L
and
the
output
at
pin
12
of
UI
2
is
applied
to
pin
1
of
UI
2.
When
the
external
reference
frequency
is
input,
pin
6
of
U10
goes
to
H,
pin
1
of
UI
2
goes
to
L
and
pin
2
where
the
external
refer
ence
frequency
is
input
becomes
effective.
Pins
3,
4,
5
and
6
of
UI
2
outputs
divided
frequencies
for
tape
speeds
of
30
ips
through
3-3/4
ips.
Two
speeds
from
among
these
are
selected
by
jumpers
and
two
speeds
are
again
selected
by
UI
1.
5)
Motor
start/stop
circuit
The
motor
is
started
by
the
PLAY
signal.
Pin
14
of
U4
goes
to
L
by
the
PLAY
signal,
UI
4,
Q2
and
Q4
switched
off
and
the
motor
is
started.
When
the
PLAY
signal
goes
to
H
by
depressing
the
STOP
button,
pin
6
of
U5
is
reverse
biased,
pin
7
of
U5
drops
near
to
the
minus
poer
supply
voltage
and
a
reverse
voltage
is
applied
to
the
motor
to
brake
it.
As
the
motor
revolution
drops,
the
source
voltage
of
QI
which
is
the
output
of
the
F/V
converter
A,
goes
up.
When
the
motor
revolution
slows
down
to
where
the
voltage
at
pin
3
of
U4
becomes
higher
than
the
voltage
set
at
pin
2
of
U4,
pin
1
of
U4
goes
to
H,
U14,
Q2
and
Q4
switches
on
and
the
motor
stops.
FG
REF
U6
I
U6
13
U7
I
U7
13
U8
I
U8
2
U8
13
U7
12
U2
15
U3
5
Q3
S
—
UI5
C
—
REF
Fig.
3.18
27

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