High/Low-Pass filter calculations
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 23rd January 2005, 06:52 PM #1 Matttcattt   diyAudio Member     Join Date: Feb 2003 Location: Bristol High/Low-Pass filter calculations Im planning to build some active filters. Searching the web came up with the perfect document - The SLOA093 ap note from TI on active filter design. One simple question. What units do the calculations use? Farads and Ohms right? I dont want to buy components 1,000,000 time too large. :P __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".
12 Cents
diyAudio Member

Join Date: Nov 2004
Re: High/Low-Pass filter calculations

Quote:
 Originally posted by Matttcattt What units do the calculations use? Farads and Ohms right? I dont want to buy components 1,000,000 time too large. :P
I think it assumes just Farads and Ohms. Of course you can enter Millifarads, but be sure to treat the result as Milliohms

 23rd January 2005, 09:53 PM #3 Matttcattt   diyAudio Member     Join Date: Feb 2003 Location: Bristol Thanks. I just wanted to get a second opinion. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".
 23rd January 2005, 10:24 PM #4 rpapps   diyAudio Member   Join Date: Jul 2004 Location: nowhere of interest Filter Calcs Hi Matttcattt The calculations are intended for basic units ie. ohms, farads and hertz. Just use the appropriate multiplier when entering your component values. Eg. 100 pF = 100 x 10 to -12 power, 0.1 mF = 0.1 x 10 to -6 power, 1k ohm = 1 x 10 to +3 power, 10 KHz = 10 x 10 to +3 power. You get the idea? Hope this helps. Cheers Rob
 24th January 2005, 10:55 PM #5 Matttcattt   diyAudio Member     Join Date: Feb 2003 Location: Bristol Thanks. I dont like standard form (1x10^-6F). I prefer long decimals (0.000001F). __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".
 24th January 2005, 11:04 PM #6 pinkmouse   diyAudio Moderator     Join Date: Apr 2002 Location: Rotherham, England You could try the sim on National's website, Webbench, it uses real world values. __________________ Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
 25th January 2005, 10:17 PM #7 Evan Shultz   diyAudio Member   Join Date: Jun 2004 Location: California, USA TI also has a rather powerful program called FilterPro that will automate much of this for active filters. You can choose topology and choose some components while allow the rest to be auto-selected. I'd check it out.
thomas997
diyAudio Member

Join Date: Feb 2004
Location: Vancouver
Quote:
 Originally posted by Evan Shultz TI also has a rather powerful program called FilterPro that will automate much of this for active filters. You can choose topology and choose some components while allow the rest to be auto-selected. I'd check it out.
I agree, simple and easy to work with.

 26th January 2005, 06:38 PM #9 Matttcattt   diyAudio Member     Join Date: Feb 2003 Location: Bristol I've already calculated the values and ordered the parts now, but I'll have a look anyway. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

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