[sdiy] ASM VCF Problem

[Frédéric Piron]

hi all,

Well i'm still in need of some help with the vcf problem, so if a kind  
soul has any ideas on how I can resolve it, they're more than welcome.

Thanks for your time,

Fred



Le 29 mars 04, à 12:14, Frédéric Piron a écrit :

> 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.
>>>
>>>
>> ______________________________________________________________________ 
>> _
>> Ken Stone   sasami at hotkey.net.au or ken at cgs.synth.net
>> Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
>> Australian Miniature Horses & Ponies  
>> <http://www.blaze.net.au/~sasami/>
>>
>>
>>
> ----------------------------------------------------------------------- 
> ---------------------------
> Frédéric Piron
>
> COTA asbl
> 7, rue de la Révolution
> 1000 Bruxelles
>
> Tél. : 02/218 18 96
> Fax : 02/223 14 95
>
> frederic.piron at cota.be
> http://www.cota.be
>
>
>
>
------------------------------------------------------------------------ 
--------------------------
Frédéric Piron

COTA asbl
7, rue de la Révolution
1000 Bruxelles

Tél. : 02/218 18 96
Fax : 02/223 14 95

frederic.piron at cota.be
http://www.cota.be