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 24th January 2008, 11:07 PM #1 nhuwar   diyAudio Member     Join Date: Jan 2007 Location: Cypress Texas Formula question Ok just have a quick one. The formula 1/2piRC= -3db point The question I have is do I put in the capacitance is the value in farads or microfarads. If the value is farads is the answer to the formula in hertz ??????? Thanks for the help. Nick
 24th January 2008, 11:14 PM #2 Sherman   diyAudio Member   Join Date: Feb 2004 Location: Chicago area The C is in farads and the answer is in hertz. The formula I have in my "useful formulas" spreadsheet- 1/(2*Pi*R*C)*1,000,000 That way I can put the value in in microfarads since the spreadsheet is designed to use "real world" values and the formula converts it for me. __________________ --Sherman
 24th January 2008, 11:28 PM #3 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland C in farads, R in ohms. Or R in megohms, C in microfarads. Both give you the answer in Hz. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 25th January 2008, 12:12 AM #4 nhuwar   diyAudio Member     Join Date: Jan 2007 Location: Cypress Texas Gracias Nick
 5th February 2008, 12:12 AM #5 nhuwar   diyAudio Member     Join Date: Jan 2007 Location: Cypress Texas Wait a sec I missed something before if you use microfarads and megohm is your out come in megahertz? Nick
 5th February 2008, 12:44 AM #6 ErikdeBest   mostly thinkerer diyAudio Member   Join Date: Mar 2003 Location: Zürich Hi As SY said, the answer is still in Hz. The F unit is divided by 1000000 to obtain microF. This 1000000 is multiplied with the R, to obtain the megaR. 100k is 0.1M (ohm). 100nF is 0.1microF. and so on... Good luck, Erik __________________ my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
 5th February 2008, 12:45 PM #7 nhuwar   diyAudio Member     Join Date: Jan 2007 Location: Cypress Texas Ok I was just making sure. I was getting some werd results thars all. I think my problem was I was thinking high pass instead of low. Nick
 5th February 2008, 02:46 PM #8 richwalters diyAudio Member     Join Date: Sep 2003 Location: Schwartzwald Reminds me of the early days when a 1mfd marked cap was actually 1uF in disquise ! some dreadful mistakes were made. A true 1mfd cap is quite a different animal. SY remember this ? r:-
 5th February 2008, 04:43 PM #9 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland Yes, indeed. Especially on cheesy paper caps (which are now all the fashion rage). Sadly I'm also old enough to remember mmf. And cps. I remember that QST, in one of their April issues (maybe 1967, 1968?), published a nomograph for cps to Hz conversions. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
kevinkr
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Join Date: Sep 2004
Location: Boston, Massachusetts
Quote:
 Originally posted by SY Yes, indeed. Especially on cheesy paper caps (which are now all the fashion rage). Sadly I'm also old enough to remember mmf. And cps. I remember that QST, in one of their April issues (maybe 1967, 1968?), published a nomograph for cps to Hz conversions.
I was about 9 when Batman first hit TV (1966?) and I too still remember cps, mmfd, and the physical components themselves - the electrically leaky wax covered paper things that often passed for capacitors, and those terrible carbon composition resistors with a tolerance of 20%, which always seemed to be way off the mark..
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