[sdiy] Bandpass Filter Recommendations

[Neil Johnson]

Tom,

> > I had some difficulty with the resonance. You'll find the discussion
> > on this in the archives. Ian Fritz and Neil Johnson gave me a lot of
> > help, but I never did get it going how I wanted, although I think
> > this was a fault, not the design per se. It's currently a project on
> > my "things to go back to" shelf.

One thing I found with my 3-pole filter is the connection of the two zeners is critical.  Roman's circuit has them connected across the last capacitor.  I found the leakage current through the zeners affected the signal as resonance was turned up, so I have the zeners back-to-back limiting the outer feedback path.  See schematic:

http://www.milton.arachsys.com/nj71/pdf/cesyg/vcf-sch.pdf

Cheers,
Neil
--
http://www.njohnson.co.uk