Akai GX-635D Service Manual

VELOCITY
+
PULSE
WIDTH
CONVERSION
r\
501
@
I-2.
CIRCUIT
FOR
PREVENTING CLICK
NOISE
DURING
TIMER
RECORDING
l) When
the
power
is turned
on for timer
recording,
recording must
take
place
after
the amplifier
circuit
is in full operation
or
else
click
noise
will be
recorded. Also when
the
power
is turned off,
Rec
Final Mute must operate
before
the
amplifier
circuit ceases to operate
oÍ else click
noise
will be
recorded.
This
circuit
prevents
such click
noise
from
being recorded.
2)
In
ordinary
recording, base
electric
cuÍrent
flows
to TR28
base through
R89 and
R90, and TR28
is
ON.
Therefore,
Rec Final
Mute relay
RLI
@re
Amp
P.C Board) connected
to TR28 collector
is
operating
to
supply
the signals
to the recording
head and
the recording mode
is effected.
3)
When the
power
is turned ON
at
timer recording
stand-by,
base electric current
is supplied
to
TR27
base
only while C42
is being charged
and
TR27
is
turned ON.
When
TR27 is turned
ON,
electric
potential is not supplied
to TR28
base
and TR28
is
turned off. Consequently
relay
RLI does
not
operate
and
Rec head
is not supplied
with a signal.
Since
TR27
turns off
once
C42
is
charged,
base
electric
current
flows
to TR28 base
through
R89
and
R90.
Because
relay
RLI function
only after
the ampli-
fier
circuit
is
in
complete
operation,
the click
noise
is
avoided.
4)
TR20 and
TR2l
is OFF during
recording mode
and
for
this reason C32 and C33 are
charged.
When the
power
is turned off
in this condition,
by
the
charging
voltage on C33
TR20 base
will
become lower than the
emitter in electric
potential
and
turns ON. TR2l
is
also
supplied with
electric
current thereby
and is turned
on. When
TR21
is
turned
on, C32
is discharged, and
ICI terminal 2
(Stop-)
becomes
ground
potential
through D24.
This releases
the deck
from the recording
mode
and
the stop mode
is effected.
This operation takes
place
before
the amplifier
circuit
stops and
therefore the click
noise is cut
out.
Fig.5
Block
Diagram
2.THF. SAMPLE
AND HOLD SYSTEM
SERVO
MOTOR
(SCM-200)
OPERATION
l)
Servo
signals
generally created
proportionately to
the number
of revolutions
of the motor
are
shown
either as
frequency
deviations
or voltage
deflec-
tions.
The motor
employed
in
GX-635D
uses
frequency deviation
unaffected
by time constants,
etc.,
of the
load circuit
as
input signal
to the
motor
drive circuit
through
pulse
width conver-
sion.
This
pulse
width
varies
proportionately to
the
deviations
in the number
of
motor rotations.
The
deviation
is detected,
converted
to a voltage
value,
is
held at
that voltage
until
the next servo
signal
pulse,
and
then impressed
into
the motor drive
circuit.
Meanwhile,
since
it requires
a holding
circuit
and
because 112
pulse
are
generated for each
motor
rotation, time
constants
of circuits
coming
before
the
Sample
and
Hold
circuit
can be
greatly
reduced compared
to
the conventional
voltage
deflection
detection
system.
For the reasons above,
it
features
quick response
to
motor
revolutions,
minimum
influence
by
tem-
perature,
and fewer
chances
of
faulty mechanism.
In addition,
due
to the
inclusion
of the
servo
voltage
holding circuit,
ripple content
of
the servo
voltage holding circuit,
ripple
content of
the servo
voltage has
been sharply
reduced
to result
in a
smooth
and stable
tape
transport
with a minimum
of wow
&
flutter.
L|l
20

Akai GX-635D Specifications

General

Track system	4-track, 2-channel stereo
Total Harmonic Distortion	0.8%
Outputs	0.775V (line)
Type	Reel to Reel
Heads	3 heads
Motor	2 x reel, 1 x capstan
Reel size	up to 10.5 inch reel
Wow and flutter	0.06% (7 1⁄2 ips)
Frequency response	30Hz to 26kHz (7 1/2 ips)
Signal to Noise Ratio	62dB
Dimensions	440 x 440 x 240 mm (17.3 x 17.3 x 9.4 inches)
Output Voltage	0.775V
Tape speeds	3 3/4 ips, 7 1/2 ips