[sdiy] problem with 13700 flter upper range

[Dan Snazelle]

OK

i have gone through a bunch of filters on the breadboard this week and at first was leaning toward a simple sallen and key with a vactrol for CV control. however i didnt like having to have the cutoff knob go through the vactrol...so i moved toward lm13700 based filters.

looking at this one in particular ( for low parts count)

http://www.musicfromouterspace.com/analogsynth/SOUNDLABMINISYNTH/images/synthkit_vcf_vca_001.gif

which is the soundlab filter.

right off the bat though i ran into problems, the first being that it's highest cutoff seems to be lower than 12k. whatever i put into it (drums mainly) gets a ton of high end chopped off.


I have reduced the input resistors, tried messing with the filter caps (using 820 pf polystyrene), etc. BUT i dont know enough about filters to figure out what might be wrong with my top frequency.

I have tried with both CV ins AND the cutoff pot. 
I dont want to fry the LM13700 so i am afraid to mess with the resistors on the + and - rails of the cutoff pot too much. (i assume plugging the + end of the pot straight into +v instead of using the resistor will bring up the High end a little bit,  in face i tested it for a moment. but it sill wasnt as high as my dry signal.

SO what can i do?? is it just a (feature) of this filter? should i try the wasp filter instead?

or go back to my lowly sallen key?

thanks guys!!!

--------------------------------------------
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http://www.myspace.com/lossnyc


http://www.soundclick.com/lossnyc.htm


http://www.indie911.com/dan-snazelle
(or for techno) http://www.myspace.com/snazelle