Fostex B-16 - Page 21

Volt 
PHOTO
INTERRUPTER
OUTPUT
0 TAPE TENSION INCREASE-*-
Fig. 4.0
For the takeup side, the photo-interrupter output fed to U16-3, is compared
with U16-2 and output at U16-1. Then, passing through a phase advance circuit,
is applied to the motor drive circuit consisting of U17, Q38 and Q101
(current feedback is applied by R1S8) to drive the motor. The motor torque
thus created puts tension on the tape which moves the tension arm and its
position is detected and output by the photo-interrupter. As shown in Fig.
4.8, when tape tension rises, the photo-interrupter output drops and U16-1
also drops. In response to this, the motor drive circuit input also drops
and as a result, motor torque decreases to reduce tape tension. When tape
tension falls, the operation is reversed to increase the tape tension.
As a result of these operations, tape tension is maintained at a constant
figure. This constant figure can be established by the voltage input to
U16-2. In other words, the emitter output of Q37 is the reference voltage
by which tape tension is established.
This reference voltage is set by R3O2 for the EDIT mode, by R300 for the
PLAY mode when Q15 is ON, and by R301 for F.FWD mode when Q36 is ON.
It must be noted that since R300 and R301 are wired in parallel with R3O2,
the adjustments of the former two pots will be affected by any change of
the latter pot. The situation is the same for the SUPPLY side.
2) FAST WINDING speed control circuit
Tape speed is controlled by the motion pulse signal from the counter section.
Q44 is switched by the motion pulse and a saw tooth wave generated by the
integration circuit of C51 and a resistor. The peaks of this saw tooth wave
is detected by D46 and C52, then output from the emitter of Q45.
i- ‘ 964 FOSTEX CORP. 8268 066100 18