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Pass: Constant Current Source Filter Networks
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Old 27th December 2006, 10:22 PM   #1
AudioAngel is offline AudioAngel  Germany
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Default Pass: Constant Current Source Filter Networks

Hello,

just read the paper on firstwatt.com concerning the filter networks for a constant current source amplifier like F1. But I'm a little bit confused about getting the part values. Therefore can somebody explain it to me so that I an verify my thoughts? Let's say, we want to build an 2nd order Bessel filter with a cutoff frequency of 1kHz and 1K ohm load (just as an example). What re the component values?

Greets,

Raphael
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Old 27th December 2006, 10:42 PM   #2
Nelson Pass is offline Nelson Pass  United States
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Pass: Constant Current Source Filter Networks
Referring you back to that article, on fig 5A you see a 2 pole
high pass and low pass network (in series) both of which are
set for 1 KHz. You need only multiply the inductance values by
125 and the divide the capacitor values by 125 to scale the 8
ohm load to 1 Kohm. You can use these two networks alone -
each does not require the other. The specific alignment of
can be tweaked with modest variations, and of course you can
multiply/divide values of the inductors and capacitors to scale
the filters to other frequencies.

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Old 27th December 2006, 11:36 PM   #3
AudioAngel is offline AudioAngel  Germany
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Ok, thank you Nelson.
I didn't recognized that they are set to 1kHz.
So the only way to get the desired Bessel characteristic is try and error unti it fits in?

Raphael
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Old 28th December 2006, 07:50 PM   #4
Nelson Pass is offline Nelson Pass  United States
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Pass: Constant Current Source Filter Networks
If you are mathematically inclined, you can calculate the
exact LC values. I don't personally get excited about this
when we are dealing with loudspeakers - precise filter
types are not usually optimal due to the vagaries of the
driver response.

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