Question about PAIA 2720-3L LPF design

lostinpurdy · Joined: Nov 16, 2007 Posts: 37 Location: Gig Harbor

The PAIA 2720 LPF seems to be a simple enough design for me to put together but I do have one question about it though - is it possible to modify it in a way so that it's possible to control the resonance as well, and what would be the simplest method to accomplish this? I would really like to keep the circuit as simple and low parts as possible.

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Psyingo · Joined: Jun 11, 2009 Posts: 242 Location: Canada

The paia 2700 lpf doesn't have resonance. You would have to do some serious modifications to it to make it resonant.

If you want a simple resonant filter, i hear the wsg filter by music from outer space is popular.

valis · Posted: Sun Nov 11, 2012 11:51 am Post subject:

As far as PAiA filters go, it sounds like the 2720-5 resonant BPF might be a better option for you. It's a simple circuit. You can change the range of the filter to better suit your needs by proportionally altering C3, C4, and C5. Halving the values should double both the high and low end of the filter.

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Cynosure · Posted: Sun Nov 11, 2012 1:10 pm Post subject:

I have something very similar to the Paia filter that is both lowpass and bandpass. I haven't posted the schematic yet because I am still working on soldering it all together with the rest of the project. I will cut out the filter part and post it later today.

Cynosure · Posted: Sun Nov 11, 2012 2:42 pm Post subject:

Ok here is the schematic.

It is the same filter from the LM13700 datasheet but with a resonance loop and pot added to the first stage of the filter.

The control voltage is from -5V to +5V, but if you tweak the values of C47 and C48 you should be able to get it to work from 0V to +5V.

If all you want is the lowpass portion then you can leave out the TL opamp and just take the output from C37. That part was just added to boost the bandpass output level.

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Cynosure · Posted: Mon Nov 12, 2012 7:17 am Post subject:

For some reason your schematic wasn't showing up for me and I thought you meant the svf in the fatman. The one you are looking at is actually a lot mor simple than the one I posted.

It looks like a sallen key filter. Maybe try looking at some schematics for those and see how they add resonance. Or try just creating your own feedback loop with a buffer like in the MS20 filter. Try by starting with A3 from this:

http://www.uni-bonn.de/~uzs159/rs20.png

Psyingo · Joined: Jun 11, 2009 Posts: 242 Location: Canada

Neither the 2720-3L or 2720-3b are sallen keys. Resonance will not be as easy as adding a feedback path unfortunately.