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Quality of LP filters for PWM - for audio performance

PostPosted: Tue Oct 05, 2004 6:31 pm
by John K5PRO
Maybe its been posted here before. Jim Tonnes (formerly of Collins Broadcast) has some useful software and analysis of low pass filters used in PWM audio amplifiers for broadcast/amateur modulators. ... wmham.html

His main website has software and other tips. Its at:

PostPosted: Wed Oct 06, 2004 8:28 am
by frank carcia
Very Good find. Notice the corner of the first filter section is a lot lower than the second. Also the first inductor is larger than the second. fc

PostPosted: Fri Oct 08, 2004 7:29 am
by ke1gf

There are lots of good points in this page that you posted.

I'm wondering if Blaine could make the page sticky, understanding jim's stuff would be a great help to the PWM beginner.

I downloaded Elsie a few weeks ago, it doesn't seem to want to run on my WinXP,SP2 machine but runs OKFINE on the WIN98 box, haven't tried it yet under WINE.

Speaking of WINE, SWCADIII runs good under it.


Yes, good paper.

PostPosted: Thu Nov 25, 2004 5:12 pm
by N9NEO
I just had an interesting email volley with Jim T. He is putting some rigs together to get back on the bands. Hope he stops by here. He would be a good contributor.

Below are links to more of his app notes and also some cool software.


Re: Quality of LP filters for PWM - for audio performance

PostPosted: Wed Apr 16, 2014 5:19 pm
by Brian K1LI
I found Jim's note at the end of his paper, re: scaling the filter's input and output impedances, to be somewhat cryptic. A freeware program called AADE Filter Design allows the designer to explicitly set the filter's input and output terminating impedances. I validated my design by porting it to LTSpice and to Elsie.