Formula question

nhuwar · 24th January 2008, 11:07 PM

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

Sherman · 24th January 2008, 11:14 PM

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.

SY · 24th January 2008, 11:28 PM

C in farads, R in ohms. Or R in megohms, C in microfarads. Both give you the answer in Hz.

nhuwar · 25th January 2008, 12:12 AM

Gracias

Nick

nhuwar · 5th February 2008, 12:12 AM

Wait a sec I missed something before if you use microfarads and megohm is your out come in megahertz?

Nick

ErikdeBest · 5th February 2008, 12:44 AM

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

nhuwar · 5th February 2008, 12:45 PM

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

richwalters · 5th February 2008, 02:46 PM

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:-

SY · 5th February 2008, 04:43 PM

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.

kevinkr · 5th February 2008, 05:02 PM

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..

24th January 2008, 11:07 PM	#1
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball 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/(2PiRC)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 diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	C in farads, R in ohms. Or R in megohms, C in microfarads. Both give you the answer in Hz. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

5th February 2008, 12:44 AM	#6
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	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, 04:43 PM	#9
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	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. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

25th January 2008, 12:12 AM	#4
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Gracias Nick

5th February 2008, 12:12 AM	#5
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Wait a sec I missed something before if you use microfarads and megohm is your out come in megahertz? Nick

5th February 2008, 12:45 PM	#7
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball 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: Alps:Tube amp designs over 150W, SMPS guru.	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:-

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