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Old 24th January 2007, 03:46 AM   #1
diyAudio Member
Join Date: May 2004
Location: Sydney
Default Active Single Stage Butterworth 3rd order HP Calculator?


Where can I find it on the net? Have you got a link?

I have found the excellent site by Uwe Beis (thank you Uwe!) but it has only the LP Calculator. I don't know how to convert a 3-pole single stage LP to a HP.

Any links or information will be highly appreciated.

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Old 24th January 2007, 10:18 AM   #2
diyAudio Member
Join Date: May 2004
Location: Hertfordshire
You can use Uwe 's excellent on-line calculator and then transpose the capacitors to resistors and resistors to capacitors keeping the impedances the same at the cut-ff frequency so for a 50Hz low-pass filter
First column is Uwe's calculated values for a 50Hz filter
Second column is my transposition using Z=1/2piFC
R1 = 5.84k c1 = 545nF
r3 = 9.5k c3 = 330nF
r5 = 8.5k c5 = 374nF
c2 = 680n r2 = 4.7k
c4 = 1uF r4 = 3.18k
c6 = 100n r6 = 31.8k
The second column gives a high pass filter with a cut-off of 50Hz and a slope of 18dB per octave
Only problem is that Uwe has chosen the LP capacitors to be standard values and the new values are not standard, although I could not resist rounding r2 to 4.7K and c3 to 330nf.
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Old 24th January 2007, 11:01 PM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Uwe's use of unity gain S&K forces one to adopt quirky values for the capacitors.
If one adopts the equal value component S&K then the gain setting resistors can be chosen to make the Q=1 completely independant of the frequency setting components where R1=R2=R and C1=C2=C. Much easier to select suitable capacitor values and by using either a pair of parallel resistors for each R or a series pair for each R to obtain any frequency with standard E24 values.
National Semiconductor ap note 779 and oa26 apply.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 28th January 2007, 09:37 PM   #4
diyAudio Member
Join Date: May 2004
Location: Sydney
Thanks guys. I have got it.
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