What the hell is the equation for T-filter? <SOLVED>

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Sorry, I didn't look closely enough at that ASCII schematic you linked.

That is, in fact, just a bridged-T filter.

Look at the figures and text at the bottom of this page:
http://www.geofex.com/Article_Folders/EQs/paramet.htm
 
Hi!

Dave, am I mistaken or were the calculations for these filters in the Tremaine Passive Book you scanned?

Hope you sort it out Jaakko...

Cheers Tom
 
If you want a more precise answer, use 159155 instead of 159000. This is kind of academic anyway because of the tolerance of typical caps.

Where does this number come from? It's a kind of shorthand. The formula for capacitive reactance is

Xc = 1 / 2pi(FC)

Where Xc is capacitive reactance in Ohms, F is frequency in Hertz, and C is capacitance in Farads.

The reciprocal of 2pi is 0.159154943
Since it's generally inconvenient to deal in Farads, we can multiply 1/(2pi) by one million and arrange the formula like this

Xc(Ohms) = 159154.943 / Hertz * microfarads
 
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