RFI fc

zahlm · 20th May 2004, 03:26 AM

Which fc is typically used to filter RFI signals in a preamp? Is 190KHz a good frequency or is too high?

Thanks, Zahlm

dmfraser · 27th May 2004, 12:31 AM

I generally set my filters with a 55 KHz knee and an 18 db per octave roll-off. However, with Class D amplifiers, I use 30 KHz and a 24 db per octave rolloff.

MBK · 27th May 2004, 12:45 AM

I usually see 150 kHz to 200 kHz as Fc, with anything from 1st to 3rd order filters.

The reason why ppl use higher Fc values such as these is that in a chain with many cascaded RFI filters, you may end up with detectable phase shift in the audio band if you use just 30 or 50 kHz.

20th May 2004, 03:26 AM	#1
zahlm diyAudio Member Join Date: Mar 2004 Location: Barcelona	RFI fc Which fc is typically used to filter RFI signals in a preamp? Is 190KHz a good frequency or is too high? Thanks, Zahlm

27th May 2004, 12:31 AM	#2
dmfraser diyAudio Member Join Date: Dec 2003 Location: Orange County, CA	Fc I generally set my filters with a 55 KHz knee and an 18 db per octave roll-off. However, with Class D amplifiers, I use 30 KHz and a 24 db per octave rolloff. __________________ Dan Fraser

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27th May 2004, 12:45 AM	#3
MBK diyAudio Member Join Date: Apr 2002 Location: Singapore	I usually see 150 kHz to 200 kHz as Fc, with anything from 1st to 3rd order filters. The reason why ppl use higher Fc values such as these is that in a chain with many cascaded RFI filters, you may end up with detectable phase shift in the audio band if you use just 30 or 50 kHz.

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