Self-Tuning AF Filter

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	Self-Tuning AF Filter
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Parts List:
Component:	Value:	Datasheet:	Qty:
Resistor	10K	Not Available	05
Resistor	7.5K	Not Available	01
Resistor	2.7K	Not Available	01
Resistor	15K	Not Available	02
Resistor	33K	Not Available	01
Resistor	100K	Not Available	01
Resistor	1.5K	Not Available	01
Capacitor	2.2nF	Not Available	02
Capacitor	10pF	Not Available	01
Capacitor	1nF	Not Available	02
Capacitor	220nF	Not Available	01
Capacitor	33pF	Not Available	01
Transistor	2N4447	Not Available	01
Transistor	2N3645	Not Available	01
IC	LM201	Available	05

Supply voltage is +15v and -15 volts and is supplied to all OP-Amps. The OP-Amp with the 10pf compensation capacitor is the filter which is tuned by the 2N4447 FET, acting as a variable resistor. The remaining OP-Amps form comparators, (the one with no compensation capacitors) an integrator (the middle one) and a Fifferentiator (bottom right). These adjust the frequency of the filter so that there is a 180 degree phase difference between the IN and OUT signals to the filter. This will only occur when the filter is tuned to the incoming audio frequency. With the values given, the filter will track an incoming tone from 330 Hz to 3KHz.