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Old 22nd April 2005, 06:06 PM   #241
Bricolo is offline Bricolo  France
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I'm sure about that Having all poles placed on the same circle and equally spaced, in the s-plane, is caracteristic of the Butterworth alignment.
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Old 22nd April 2005, 06:48 PM   #242
AndrewT is offline AndrewT  Scotland
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Hi Bricolo,
1 pole Butterworth use Q=0.7071
2 pole Butterworth use Q=0.7071
3 pole Butterworth use Q=1 & Q=0.7071
4 pole Butterworth use Q=1.3066 & Q=0.5412
L-R2 use cascade Q=0.7071 ( 2*B1 )
L-R4 use cascade Q=0.7071 ( 2*B2 )
L-R6 use cascade Q=1 & Q=0.7071 ( 2*B3 )
L-R8 use cascade Q=1.3066 & Q=0.5412 ( 2*B4 )
As you said, all these filters are set at the same Xover frequency.
Do you need the gain settings to achieve these Q values?

Have you read LeCleach on xover modification yet?http://freerider.dyndns.org/anlage/LeCleach2.zip Then you have to change frequencies.
Can this mod be modelled on Moxlite?
Has anyone listened to this mod yet?
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Old 22nd April 2005, 07:16 PM   #243
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For a first order filter, the Q does not apply.

Q can only be defined for a second order function.

\Jens
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Old 23rd April 2005, 08:41 AM   #244
AndrewT is offline AndrewT  Scotland
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Hi Bricolo,
would you like to start a new thread (or wiki) & explain that poles, circles & s-plane theory? and how to use it in practice.
I would like to learn more.
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Old 23rd April 2005, 10:20 AM   #245
Bricolo is offline Bricolo  France
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Hi,

It's not very usefull to set up an audio filter, since everything is already pre-calculated and many tables are available.

But if you want to have a deeper look at the theory, and where those tables come from, you can read those pages:

Do you know what a s-plane is? Basicly, it's a map where your poles and zeros are placed, according to theyr Real and Imaginary part.
This chapter seems good
http://www.phys.ualberta.ca/~gingric...00000000000000

And for Butterworth filters:
http://www.microindustrie.com/dsp/b-dis.htm
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Old 23rd April 2005, 10:42 AM   #246
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Tables are always normalized to a frequency, when using tables to design a filter, you also should look up frequency scaling as this is needed to calculate the parameters in the non normalized filter.

Frequency scaling "moves" the corner-freq from the normalized frequency to where you want your filter to have it's cornerfrequency.

I hope I make sence

\Jens
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Old 2nd May 2005, 09:17 PM   #247
AndrewT is offline AndrewT  Scotland
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Default Butterworth 4 pole

Hi all,
I have attached an excel spreadsheet to calculate the caps & resistors for a 4 pole low pass filter.
It uses 2 cascaded unity gain stages (moxlite) with staggered Qs of .54 & 1.3 to achieve a total q=0.7071 for Butterworth roll off.
Each stage could be used for odd values of Q if Mox shows the need to tailor the Xover to your speakers.
Attached Files
File Type: zip unitygain4polefilter.zip (12.2 KB, 40 views)
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Old 3rd August 2012, 12:12 PM   #248
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Does anyone have a copy of the MOX II opamp assembly guide? Referenced in post #4.

Thanks,

Vince
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Old 3rd August 2012, 03:41 PM   #249
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Vince,

Here you go.

Anidian Audio - MOX - Opamp assembly page 1
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Old 3rd August 2012, 03:54 PM   #250
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I needed the link, as well. Thanks

I hope tiroth is doing well...
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