High pass second order filter

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Audioguru said:
What is a "critical frequency"? Highpass and lowpass filters have a "cutoff frequency" where it is just beginning to filter and the output level is -3dB from the input level.
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This (..from the input level) applies to unity gain filters only.
In all other cases the cutoff frequency is defined for a level which is 3 dB below the maximum output (dc for lowpass).
 

What exactly you did for sorting it out? Because so many suggestions given to you...
 

So I can work out the critical frequency by

1/2 PI Square root R1R2C1C2

1/2PI Square root 22000x5600x10x10 = 0.00000143388

Why am I in negative values?

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Surendhar M said:
What exactly you did for sorting it out? Because so many suggestions given to you...
Click to expand...

I put another 9v input to R1 at ground

To work out the gain, I did 20log output/input
 
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I cannot detect any negative values.
And you capacitances are 10 Farads?
 

Yeah wasn't thinking straight when I said negative, oh yeah of course!!

Maths argh!!!!

nF

So 1/2Pi square root 22000x5600x10 -9x10 -9

correct?
 
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The highpass filter does not have "a critical frequency" instead it has a cutoff frequency.

Are you still in school doing arithmetic? Why don't you simulate it or use an online calculator like this one?
 

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My assignment asks for the critical frequency, must be cut off then
Yes my maths isn't good. ( I Know)

I have used a online calculator but I would like to show the working out
 

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