[sdiy] Pot-based SVFs

Tom Wiltshire tom at electricdruid.net
Thu Mar 13 15:45:53 CET 2008


Aaron,

The Analog Devices interactive filter design tool (needs java) will  
give you a schematic for a state-variable filter, among others. Great  
tool, actually. I'd mention it in a lecture anyway!

http://www.analog.com/Analog_Root/static/techSupport/designTools/ 
interactiveTools/filter/filter.html

Hope this helps,
Tom


On 13 Mar 2008, at 06:47, Aaron Lanterman wrote:

> Tomorrow's lecture is on State Variable filters.
>
> I have examples to show from the Oberheim SEM and the EML-101,  
> which I understand fairly well.
>
> I'd also like to show a couple of real-world examples of non- 
> voltage-controlled SVFs - i.e. ones controlled with regular pots -  
> before I dig into the voltage-controlled ones. I'm looking for  
> something with a real-world world schematics, i.e. not idealized  
> textbook schematics. Any ideas?
>
> I ran across this design by M. Danielson:
>
> http://home.swipnet.se/cfmd/synths/schematics/svf1.pdf
>
> But something doesn't look right to me. Both feedback loops should  
> be negative, if I understand the universe right; going through two  
> integrators and then into the - input of the op amp maps sense to  
> me, but taking the output of the first integrator and running it to  
> the negative doesn't, since that looks like positive feedback. I  
> think it should be going to the positive terminal of the first op amp.
>
> The initial input is going into the negative terminal, but that's  
> incidental.
>
> Is there something I'm missing?
>
> - Aaron
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