Sony PS-X7 - Page 29

Since the emitter voltage of Q203 is determined
at this time by. the reference voltage, Q203
turns on when its base voltage (sawtooth wave)
exceeds the total voltage (emitter voltage plus
+Vpp). So a negative pulse will appear on the
collector of Q203.
2. If the rotational speed slows down, the fre-
quency of the sawtooth wave will be low.
Also, the output pulse width increases, because
the on-time of Q203 becomes long.
Qn the other hand, if the rotational speed
increases, the frequency of the sawtooth wave
will be high. Also, the output pulse width
becomes narrow, because the on-period of Q203
becomes short.
{When rotational speed
slows down.) increases.)
Q203
io).
a.
=
_
base voltage. 1 reference (
{ | voltage
H at
! 4
I it
0203 ep +
collector voltage Ie it rat ar
! ' |
becomes standard becomes
~ wider narrower
Fig. 1-2.
Pulse Signal Amplifier
Besides amplifying pulse signals, Q205 also serves
as a phase inverter which feeds positive pulse signals
to the next stage.
Smoothing Circuit (low-pass filter)
This smoothing circuit has two filters (one is
made up of R217 and C205, and the other is IC1-1,
R218, R219, C206 and C207). These filters operate
as an integrating circuit which converts the pulse
signals into dc signals (the voltage level being in
proportion to pulse width).
DC Amplifier Circuit
The dc amplifier (that also serves as a low-pass
filter), uses IC1-1, and amplifies the dc output signals
from the previous stage.
Speed Selector Switch (S2)
1. The circuit time constant is changed by simply
changing the resistance connected to the base
of Q203.
SONY-00830 / DRUCK 13
(When rotational speed
PS-X6/X7 PS-X6/X7 | |
2. The time constant for 45 rpm is designed to be
faster than that for 33 rpm.
3. Consequently, when switching the speed selec-
tor switch from 33 to 45 rpm, the collector
output pulse width of Q205 is widened, thereby
increasing the level of the low-pass filter DC
output signal. Motor speed is thus increased,
followed by re-application of the servo control
mechanism.
4. When switching back to 33 rpm, the reverse
sequence of events takes place.
45 rpm
reference
7 ™ voltage
33 rpm
Fig. 1-3.
Servo Control
If for. any reason, motor speed decreases or
increases, even by the slightest degree, the servo
control mechanism is activated to correct for the
deviation, and returns the speed to the reference
standard value.
1. If the motor speed is decreased slightly, the
frequency of the MG head output signal
decreases. This signal is applied to the phase
control circuit (IC2) for phase comparison.
The resultant output, of decreased voltage level,
is then sent to the servo control. And since
the base voltage of Q204 is reduced, the emitter
voltage (reference voltage) of Q203 also
decreases, resulting in the width of the Q203
collector output pulse being widened.
2. The de output voltage from the low-pass filter
consequently decreases, thereby increasing
motor speed back to the original standard value.
3. If, on the other hand, motor speed is increased
by some external influence, the servo control
mechanism reduces speed in the reverse manner
of that described above.
When rotational speed
increases:
Q203 base voltage
reference voltage
When rotational speed
slows down:
Fig. 1-4.
2. Maintaining Forward Rotation (See Fig. 2-3)
1. When a® signal is applied to the input terminal
of the Hall elements, the motor is turned in the
forward direction, but when a © signal. is
applied, the motor is turned in the reverse
direction. Therefore, the reverse rotation that
is caused by applying © input serves as a brake
for rapid stopping of the turntable.
(Conventional speed reduction systems use the
phenomenon of hysteresis loss or mechanical
loss.)
2. F-V converter circuit
This circuit converts the frequency of the MG
head output signal into a voltage signal in
accordance with the curve as shown in Fig. 2-1.
©
Ve.v
0 f
I
0 I
—= four v2 1
foc (33 rpm: 284 Hz)
Fig. 2-1. Fig. 2-2.
This curve shows. “frequency against output
voltage”’ for both forward and reverse rotations.
3. DC amplifier (IC1-1) operation
The output level of IC1-] is determined by the
relationship:
Vout = (V9 In - V°In) x Gain,
or VouT= V° IN x Gain when V°IN is OV.
In this equipment, output levels of approx.
~-1:5V to +13V are possible by applying ©
voltage to V°y through Q207 and R223.
When the speed selector is instantly switched
from 45 rpm to.33 rpm, V®yy becomes OV,
V©in becomes. positive, and Vout minus,
thereby activating the brake operation.
4. If the frequency of the MG head exceeds foc
during forward rotation, Voyr becomes 0. or
minus, thereby slowing down rotational speed.
But during reverse rotation, the result is an
acceleration of the reverse rotational action.
5. In order to prevent such “run-away”’ accelera-
tion, a switching circuit consisting of Q210,
Q209, and Q208 is employed, thus maintaining
forward rotation.
Norma! Operation
1. For normal operation, the emitter of Q210 is
fixed to a level of -0.5V by D203.
ie)
\
\
i
!
i
Since the base potential of Q210 is normally
Kept at about 1.5 V, Q210 turns on.
Since the base of Q209 is -0.5V, Q209 turns
off. Q208 also turns off, and then Q207 turns
on.
>-
® signal is thereby applied to the © input
terminal of ICI-1 through R223.
ON +{OFF) = ON -» {OFF} OFF-> {ON} ON->{OFF)
Q207 Q208 a209 Q210
Q205
toH
Halt
Conditions in brakes (
to reverse rotation case.
Fig. 2-3.
Reverse Rotation
I.
i)
When operating too fast during reverse rotation
(when the frequency of the MG head output
signal exceeds fy,), Q205 is turned off and no
signal is obtained on the ® input terminal of
ICi-1. The output level of ICI-1 then drops
from the normal 1.5V (relative to ground) to
less than +0.5 V, resulting in Q210 being turned
off.
Consequently, the base voltage of Q209 rises in
accordance with the R231/C208 time constant,
finally turning Q209 on once the base potential
exceeds +0.5V.
Q208 then turns on, and Q207 turns off.
Consequently, no voltage is applied to the ©
input terminal of [C]-1. ,
That is, the operation of IC1-1 will be stopped,
resulting in the output level reducing to OV,
and the slowing down of rotational speed.
The MG head output frequency. consequently
drops below fog, resulting in a positive output
signal from the F-V converter, and forward
motor rotation. Once the IC1-1 output level
exceeds +0.5V, the reverse-rotation prevention
circuit is put into standby status.
This reverse rotation prevention circuit,can be
switched off again extremely rapidly. When
Q210 is turned on, C208 discharges. through
R233 to the B- bus.
1 and H2
elements
) refer
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dire
stro
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for 1
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play
corr:
light
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