AW: Good, simple filter cct required

[Haible Juergen]

	>	I'm trying to get hold of a simple bandpass or lowpass
VCF, as a circuit 
	>that can be built by first year undergrads. No specialist ICs,
just opamps. 
	>I've breadboarded the filter cct at the top of p278 of
Horowitz+Hill, and 
	>it sounds good, but no voltage control. I could add OTAs, but I
wonder if 
	>anyone has alternatives? No more than six opamps, if possible.

I would have said SEM-filter, but "no OTA" - that's hard!
And Ladder filers aren't that easy to understand to begin with ...

Maybe you show your students how they can build a simple one-opamp
low pass filter (non-CV-able), and then lead them to using diodes as
voltage controlled resistors? This would be a Korg MS-50 filter then ...

JH.