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12
OSCILLATOR
OUTPUT - CIRC UIT
FREQ
.
, - - - - - - - - - - - - - - - - - - ,
Wien- four-pole
Amptifier
AMPLITUDE
SK3
F========~ ~7
"...,n,,,,,
BU2
""~if
f i
~----<"'BUl
Slicer
Attenuator
Fig. 2. Block diagram
through the feedback network Rl6j
jC9j
jresistance setting of R26 will
also change.
The increased feedback current causes a temperature rise of the NTC
resistor, so that its ohmic value will be reduced. As a result the feedback
voltage increases, so that the output voltage will be reduced to its normal
value. C9 serves for phase compensation.
With R26 the feedback has been adjusted so that the oscillator just starts
oscillating.
The shunt resistance of the Wien bridge Rl b is connected to the amplifier
input in such away, that the base current required for transistor TSl
passes through this potentiometer. The base voltage divider is formed by
the resistor circuit Rll, Ri of TS2, R8, R7 and
R6.
On account of this galvanic coupling ofTSl and TS2, their working points
will be extremely
stable.
Emitter follower TS3 serves for decoupJing and, consequently, for
matching to output transistors TS4--TSS. These transistors are connected
as a White emitter follower, so that a very low output impedance is ob
tained.
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