Circuit Operating Descriptions
7-32
5) PB AMP
The diagram to the left is the playback amp and the gain input/output are as
follows.
Av = 1 +
The playback characteristic of VHS format can be satisfied by using Z
1
, Z
2
in
the above equation.
PB amp gain should be designed to be approximately 45dB (1KHz).
Z1
Z2
INPUT
PB AMP
OUTPUT
Fig. 7-28 PB Amp
Z
2
Z
1
Z
2
Z
1
~
~
6) REC AMP
The diagram to the left is REC AMP. The amp gain is approximately 14dB.
R
1
and R
2
that determine the gain is located inside the IC.
It is uniform and independent to frequency. Frequency characteristics should
be considered when designing rec amp. The REC amp should be the opposite
to playback characteristics.
OUTPUT
PB AMP
INPUT
R1
R2
Fig. 7-29 REC Amp
7) OSC (Oscillation)
Oscillation frequency is 70KHz. It’s size is approximately 40Vp-p. it operates on recoed mode. It is supplied to
audio erase head and full erase head used to erase already recorded signals.
Also, it conducts “AM (Amplitude Modulation)” using oscillation signals.
8) BIAS Control
Output level changes according to the impedance of F/E, A/E and R/P head connected to the coil.
9) 60KHz HPF
There must be standard signal for bias control and that signal uses HPF only to obtain oscillation signal that
comes through R/P head.
10) S/W
The switch opens when recording, shorts during playback and exterior transister is used.
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