Akai GX-636

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2) Explanation of the circuit operation (Refer to
Figs. 6, 7)
The velocity signal obtained from the motor’s
frequency generator is shaped into a waveform in
the period of “T’’ proportionate to the velocity as
in (a) on collector TR6. This signal is differen-
tiated and enters TR7 base. This makes TR7’s
collector output as in (c) and turns ON TR10
during the time of the negative pulse.
Meanwhile TR8 base is supplied with a waveform
like (d) and when it reaches the threshold level,
TR8 is turned on. A waveform (e) with pulse
' width “t,” is obtained from the collector. During
the time “T”’ that TR28 is ON, TR9 base electric
potential decreases to turn ON.
Consequently, TR11 base electric potential
increases and TR11 is also turned ON for the time
“ty a
When the period “T” varies with the velocity,
the pulse width “t,” varies according to TR8’s
threshold level. But when TR1O is on, it is con-
stant due to the time constant. So that by using
the period that TR is ON as the standard pulse,
the pulse width ‘“‘t,” is constant regardless of the
velocity.
(g) and (h) show the ON and OFF condition of
TR10 and TRil. When the electric charge that
was charged to C16 is discharged during the time
TR11 is ON “t,”’, a signal voltage of “e” propor-
tionate to the velocity can be obtained. Next, with
“e”’ as its basis, C16 is charged during the limited
time of the standard pulse width “t,”’, and by the
charging voltage “e” the charging is stopped.
The voltage is then held until the hext standard
pulse.
This voltage ‘“e” is supplied to the TR12 base and
a servo signal “E” is obtained. This servo signal
“E” controls TR13 and drives the motor.
As shown above, since “‘t;” and “‘t,” are small,
servo signal ripples are made small and a near
direct current servo signal is obtained. In addition,
the time constants of the smoothing circuit can
also be made small that phase lag factor can be
minimized.