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27th December 2006, 09:22 PM  #1 
diyAudio Member

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 
27th December 2006, 09:42 PM  #2 
The one and only

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. 
27th December 2006, 10:36 PM  #3 
diyAudio Member

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 
28th December 2006, 06:50 PM  #4 
The one and only

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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