Fostex B-16 - Page 22

Resistances in the integration circuit for generating the saw tooth wave differs
according to tape speed and, for LOW, resistors R3O8 and R221 are used; for MID,
Q42 is switched ON to put R306 and R219 in parallel with the LOW resistors; and
for HIGH, both Q42 and Q43 are switched ON to put R3O7 and R220 in parallel with
the resistor combinations for the mid speed. Therefore, the emitter output levels
of Q45 will be as shown in Fig. 4.9. The saw tooth waveform will be the same as
in Fin. 4.1 and the Q45 emitter output waveform will be the same as from U7-7
shown in Fig. 4.1.
The output of Q45 passing through U18 is applied in parallel with the tension
control voltage to the takeup side fast winding servo circuit. Therefore,
when tape speed rises, output of Q4S decreases to reduce motor torque of the
takeup side and the speed drops. On the other hand, when tape speed goes
down, the circuit reacts to raise the speed.
The output of Q45 is inverted by Q46 resulting in. an output shown in Fig. 4.10.
This output passing through U18, is applied in parallel with the tension
control voltage to the supply side fast winding servo circuit . The output of
Q46 rises in proportion to rise in tape speed and this raises motor torque
of the supply side, thus acting to reduce tape speed but will react to raise
the speed if it goes down.
As explained above, speed controlling circuits in the reel supply side and
takeup side operate to maintain tape speed at HIGH, MID and LOW with the
least effect from differences in amount of tape on either reel.
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