[sdiy] ASM VCF Problem

[Frédéric Piron]

Hi Ken,

Thanks for your fast answer.

Well it's not at all a nice sine sounding sound and there's no  
variation when i turn the knob. It seems that the filter sweeps  
correctly till 0V and then noise...(resonance pot works ok) . All i can  
say is that it doesn't sound like self-oscillation.

Fred


Le 29 mars 04, à 12:05, Ken Stone a écrit :

> if the "horrible noise" is a clear sine-like tone that's frequency  
> varies
> with the CV, it is self oscillation of the filter - quite common, and
> usually desirable. A lot of people want this ability. It does sound  
> like it
> is a bit aggressive though - perhaps you have too much gain or too much
> feedback in the circuit for whatever reason.
>
> (The above does not apply to all filters though - I get a heck of a  
> lot more
> than just sine waves out of my Sallen Key filters - period doubling  
> and all
> sorts of wonderful things.)
>
> Ken
>
>> Hi list,
>>
>> (Previous message didn't make it thru to the list so here it is
>> again...)
>>
>> Got a little problem with the VCF section of my ASM-1. Everything is
>> working (filter sweeps, etc) but when I twiddle the cutoff pot I've  
>> got
>> a big loud noise comming in. In fact it's only when the pot is in the
>> positive domain. So from -15V to 0 the filter sweeps normally and as
>> soon as it is from 0 to +15V I hear a terrible noise that replaces the
>> sound of the vco.
>>
>> Have tried changing the ic's and the trannies from the expo section
>> with no luck. Re-checked my work but still bogus.
>> I'm lost here...
>>
>> Does anyone have experienced the same problem or has a clue on what's
>> going on??
>>
>> Any help appreciated,
>>
>> Fred.
>>
>>
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> Ken Stone   sasami at hotkey.net.au or ken at cgs.synth.net
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Frédéric Piron

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