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[SOLVED] Finding center frequency (f0)

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dreamlover

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Basically we found center frequency by subtracting initial frequency from final frequency i.e. F0 = F2-F1.
But while surfing internet somewhere I found a formula of center frequency (f0) = 2CV.
The thing i am not getting is that
what C and V represent for?
From where this formula came from?
Thanks.
 

You forgot to tell us what device or what circuit you are talking about. The center frequency of my FM radio is about 98MHz. The lowest frequency is 88MHz which is 10MHz lower than 98MHz and the highest frequency is 108MHz which is 10MHz higher than 98MHz.
 

From F2-F1 subtraction you will obtain the bandwidth. The center frequency is given instead by (F2+F1)/2
sometimes it can also by defined as sqrt(F2*F1)
If for instance F1=88 MHz and F2=108 MHz, then:

the band is 108-88=20 MHz
the "usually" defined center frequency is (108+88)/2=98 MHz
the "alternative" definition for the center frequency gives sqrt(108*88)=97.5 MHz

Could you please say where did you find the formula 2CV ?
 

Instead of guessing about typos or other faults in the obviously useless formula section of the article, refer to trustworthy filter calculation tools or filter design text books.

As a first step, you may want to delete the formulas using undefined quantities (e.g. "V", "d0")...
 

The audio equalizer project is useless since the author does not show the bandwidths of its multiple feedback bandpass filters which are probably too narrow. If I had more time I would simulate them for you.

The circuit uses very old LM833 opamps and the website features an amplifier made with a TDA2003 which has been obsolete for years.

EDIT: I looked at the design of the Buffer Stage and found it to have a few serious errors:
 

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The sloppy schematic style fits well the confused formula section.

Audioguru is also right about inappropriate filter bandwidth which results in an unbelievable bad > 10 dB magnitude ripple in "neutral" position.

mfb-eq.png

A multiband equalizer should implement a neutral position with flat frequency response, like the circuit below (found at schematics.ca)

electro_harmonix_graphic_equalizer_schematic_diagram.jpg
 

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