AW: Good, simple filter cct required

[Paul Perry]

At 02:59 PM 14/10/97 +0200, you wrote:
>	>	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.
......if your students like maths, you can use those AD633 multipliers..
if they don't like maths it will be a bit opaque...

a switched resistor system (not to be confused with a switched capacitor
filter ) is conceptually simple, and you get to show them pulse-width
modulation while you are at it... and it tracks perfectly...
think the ETI synths had something like this.

paul perry melbourne australia