Pass: Constant Current Source Filter Networks

AudioAngel · 27th December 2006, 09:22 PM

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

Nelson Pass · 27th December 2006, 09:42 PM

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.

AudioAngel · 27th December 2006, 10:36 PM

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

Nelson Pass · 28th December 2006, 06:50 PM

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.

27th December 2006, 09:22 PM	#1
AudioAngel diyAudio Member Join Date: Dec 2003 Location: Verden	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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27th December 2006, 09:42 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	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
AudioAngel diyAudio Member Join Date: Dec 2003 Location: Verden	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
Nelson Pass The one and only Join Date: Mar 2001	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.