It boggles the mind.

I have a program called FilterFree.  It purports to take the grunt work out
of designing low-order analog filters.  I'm trying to design a 1st order
Butterworth BPF, centered at 60 kHz with BW +/- 2kHz.  When I add in the 3rd
stage of the filter design (which looks okay to me) provided by FilterFree,
instead of a BPF, I get a BEAUTIFUL (I mean, you could market this thing) 57
kHz sine wave, regardless of the input to the filter.

My op-amps seem to be working (at least, I can implement simple voltage
follower and amplifier circuits with them), and I was wondering if anyone
else has ever encountered this problem, or has any opinion about FilterFree.

No, I'm not going to try to ASCII art the circuit.  It's a little more than
I want to attempt.  If anyone really wants to see it, let me know and I'll
post it on my website tomorrow.  It really is a good sine wave generator;
the sine wave it generates is actually a bit more stable than the one my
signal generator is coming up with.

Mike H.

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