need help wana change 60-Hz twin-T notch filter to 279 Hz filter

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the twin-T 60-Hz notch filter work extremly well but i also need one for 279 hz or close to it were i keep getting it wrong is the band width wrong .the 60 hz twin-T notchfilter-60 db which can adjusted in r5


schematic

http://focus.ti.com/lit/an/slyt145/slyt145.pdf

http://www.radio-electronics.com/info/circuits/rc_notch_filter/twin_t_notch_filter.php

math f/c =1 /( 3.142 *r1 *c1*2)

r3=1/2 r1
c3=2*c1

:smash:
 
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