[sdiy] (easy) resonant filter

[Tavys Ashcroft]

>can anyone pont me towards the worlds simplest resonant filter schematic-i'm
>bored an want to build something, doesn't have to be voltage controllable,
>but no CEM chips (preferably, just diodes, and simple op amps). nothing
>fancy. or anything else realy simple and fun.

Actually, that's exactly what I'm looking for too.  I just bought an 
unbelievable number of opamps (400 I think) from BG Micro for about 
$8, and want to put them to use (yes, they're 741s, but I'm not 
worried about it, I'm learning).  They're quad opamp chips, so I 
figure 1 opamp for the input buffer and 3 for the filter, giving me a 
1 chip filter.  Then I could make lots of them and have them really 
tiny and give them out as party favors or something.  Is there an 
easy tuneable filter (HP,LP, or BP, resonant or not) that can be made 
with three opamps?  I also don't care about voltage control, 
linearity, a perfectly clean signal, or anything really.  I just want 
to experiment with filter design and I need a starting place.  I've 
looked around and all the schematics for filters I find require some 
sort of CEM chip.

-Tavys