[sdiy] problem with 13700 flter upper range

[Dan Snazelle]

thanks all!!

i am actually running this off of +/- 12 v at the moment and will eventually try off of two 9v batteries

the problem i had with the sallen key was mainly due to trying to get a pot for cutoff AND a vactrol both working


i was using this diagram....picture number one for the vactrol/pot reference


http://thesquarewaveparade.com/images/VtoR.jpg


overall i actually liked the sound of that filter more...the lm13700 soundlab filter did not seem very steep even with lower caps


BUT i will try everyones advice and  i will report back!!!

THANKS






--------------------------------------------
check out various dan music at:

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






----------------------------------------
> Date: Tue, 27 Jan 2009 16:47:55 +0100
> Subject: Re: [sdiy] problem with 13700 flter upper range
> From: simon.oo.o at xs4all.nl
> To: synth-diy at dropmix.xs4all.nl
>
> Dan,
>
> Smaller values of C4 and C5, will give higher cutoff. So if you change
> them go for smaller not bigger. You could try 330 pF for example.
>
> Also, the cutoff will be proportional with the current into pin 1 and pin
> 16 of IC4. In this circuit this current will ever reach less than 0.2mA
> (assuming AR and LFO voltage will be at most +9V) while the LM13700 can
> handle considerably more (absolute maximum value 2mA, but better not go
> higher than 1mA).
>
> So the other thing you could try is to halve the values of R28, R31 and R36.
>
> Dan Snazelle schreef:
>>
>> 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!!!
>>
>> --------------------------------------------
>> check out various dan music at:
>>
>> 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
>>
>>
>>
>> _______________________________________________
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>> Synth-diy at dropmix.xs4all.nl
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>>
>>
>
>
> --
> Vriendelijke groet,
>
> Simon Brouwer
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