National LMF100 Filter IC ?

[John E Blacet]

Yes, switched capacitor filters have some good points, but they have
some clock feed thru the lower audio frequencies. For example, if the
filter corner frequency is 32 Hz, then 100 X 32 = 3200 Hz. Even at
really low clock levels present in (very good) filters from say, Maxim,
or Linear Technology, the residue has to be filtered out. This can be
done by a simple VC LP tracking filter. A two pole is usually enough for
the clock. You also should use a similar filter on the input to avoid
aliasing.

For a working example of such a filter, see the Final Filtre, below:
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Regards.
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John Blacet
Blacet Research Music Electronics
http://www.blacet.com
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blacet at monitor.net
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