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Marantz SD9000 - Page 13

Marantz SD9000
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.
The
output
of
QM21
is
rectified,
smoothed
and
ap-
plied
to
the
base
of
OM19
as
a
speed
control
signal.
The
functions
of
the
servo
motor
in
the
FF
mode
are
as
follows:
*
At
the
start
of
tape,
the
left
reel
rotates
at
a
slow
speed
because
there
is
a
large
amount
of
tape.
When
the
tape
on
the
left
reel
is
decreased,
the
speed
of
the
reel
is
increased
gradually
and
the
interval
of
the
input
(trigger)
pulses
from
Pin
7
of
QM21
becomes
shorter.
With
the
trigger
pulse-interval
becoming
shorter,
the
interval
of
the
output
pulses
from
Pin
7
of
QM21
also
become
shorter.
The
interval
of
the
pulses
which
are
differentiated
by
CM17
and
fed
to
the
rectifier
circuit
become
shorter,
so
the
output
voltage
of
the
smoothing
circuit
is
increased
which
increases
the
voltage
at
the
base
of
OM19.
With
the
QM19
base
voltage
increased,
the
col-
lector
current
is
increased,
decreasing
the
collector
voltage.
Thus,
the
voltage
at
the
gate
of
QM20
is
lowered.
With
the
gate
voltage
lowered,
the
drain-source
resistance
is
increased,
lowering
the
QM0O1
output
voltage
which
decreases
the
QMO8
collector
cur-
rent.
The
OMO8
collector
current
is
the
current
flowing
into
the
reel
motor.
When
this
current
is
de-
creased,
the
motor
runs
at
a
slower
speed.
The
reel
motor
drives
the
right
ree!
disk.
If
the
motor
were
to
run
at
a
constant
speed,
the
tape
would
run
slowly
at
the
beginning
of
tape
and
at
very
high
speed
at
the
end
of
the
tape.
The
servo
motor
is
used
to
make
the
tape
speed
constant
throughout
the
entire
length
of
the
tape
by
reduc-
ing
the
speed
of
the
reel
motor
while
the
tape
is
running.
Top
view
Tu
Tei
Cor
At
Bi
Qt
@
GND
Terminal
connections
12
f.
The
pulse-width
and
voltages
at
the
beginning
and
end
of
tape
are
as
follows:
oi
Beginning
|
End
of
of
tape tape
QM214
Trigger
pulse
interval
|
50
msec
CM19
“+”’
Smoothing
cir-
cuit
output
voltage
QM19
Collector
voltage
8.8V
1.7V
QM20
Gate
voltage
0.75V
0.25V
QMO08
Collector
voltage
5.8V
Reel
motor
speed
Fast
7.8V
|
Slow
|
.
The
purpose
of
maintaining
the
tape
speed
constant
in
every
fast
tape-feeding
mode
is
to
ensure
stable
operation
of
the
program
detecting
function
ex-
plained
in
a
later
section.
.
The
semi-fixed
resistor
RM34
in
Fig.
3.7
is
used
to
determine
the
maximum
speed
of
the
reel
motor,
while
RM48
is
used
to
determine
the
range
of
speed
of
the
reel
motor
or
the
average
speed
of
the
tape.
Fig.
3-8
uPD4528C
unistable
multivibrator
Voo
Vop
Block
diagram

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