NewYorkDave

What the hell is the equation for T-filter? <SOLVED>
« on: September 21, 2004, 01:36:55 PM »
Search on "twin-t" or "twin-tee" + notch + filter


NewYorkDave

What the hell is the equation for T-filter? <SOLVED>
« Reply #1 on: September 21, 2004, 02:09:49 PM »
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

TomWaterman

What the hell is the equation for T-filter? <SOLVED>
« Reply #2 on: September 21, 2004, 05:30:06 PM »
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

NewYorkDave

What the hell is the equation for T-filter? <SOLVED>
« Reply #3 on: September 21, 2004, 05:45:53 PM »
I know the twin-T was in there, as well as various flavors of bridged-T.

I didn't scan the book, by the way. My friend Tom scanned it; I just passed it on to the folks here.

CJ

What the hell is the equation for T-filter? <SOLVED>
« Reply #4 on: September 22, 2004, 01:04:10 AM »
I wish you'd put a T filter on that damn tony llama!
 :razz:
If I can't fix it, I can fix it so nobody else can!
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NewYorkDave

What the hell is the equation for T-filter? <SOLVED>
« Reply #5 on: September 22, 2004, 09:19:02 AM »
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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