Sony PS-X7 - Page 39

In addition, the phase of the frequency signal
from the speed detection head is compared with the
reference phase of the crystal oscillator frequency.
Any difference in phase is also converted into a
voltage signal, and fed to the servo amplifier, thereby
ensuring accurate turntable rotational speed.
Since motor speed is determined by the amount
of current flowing through the motor (that is, through
the motor coils), motor speed may be conveniently
changed by simply changing the flow of current
through the Hall elements. In other words, if motor
speed tends to deviate from the reference standard
value due to external influences, the constant speed
value may be maintained by simply varying the
amount of current flowing through the Hall elements
in proportion to the amount of deviation in turntable
speed.
Phase Control
3840 Hz
7680 Hz
1C2
phase control
crystal oscillator
172"°
frequency
divider
1/2
frequency
divider
Xi
fi "ah Hz)
frequency
divider
1/44
frequency
divider
er
99
33rpm,; 71.111 Hz
1/20, 1/27
PS-X6/X7
terminal H
tt H '
terminal i H : t H
Try a wHe ot
terminal ieee ae vote H
1 1 L
' {
When rotational speed increases,
the output is raised only for the
portion of change.
When rotational speed slows down,
the output is lowered only for the
portion of change.
Fig. 4-7.
33 rpm: 142,222 Hz
45 rpm: 192 Hz
to stroboscope
Circuit
1/2
frequency
divider
33 rpm: 71.111 Hz
45 rom: 96 Hz
Q302 2SCE33A
low-pass filter
45rpm; 96 Hz
Bt Reduced when slower than
standard rotational speed output
Vv S2
S$2-1 SPEED Increased when faster than to servo
MG
head
output
93
7
45
standard
rotational
speed
amplifier
33
rom:
284.444
Hz
45 rpm: 384 Hz
Fig. 4-6.
Os