[sdiy] CEM VCF transconductance stage difference!

[Tom Wiltshire]

I don't know if it's for the same reason (gm differences in the  
transconductance stages) but some of the SSM filters use different  
cap values too. The SSM2044 uses 3 identical values and one  
different. The SSM2047 VCF/VCA chip uses 2 identical values and *two*  
different values.

If it is for the same reason, it must have been a good reason, 'cos  
everyone was at it!

T.


On 26 Dec 2008, at 21:34, mark verbos wrote:

> Jürgen from Jomox once gave me a demo of his Sunsyn, while he was  
> finishing up its design. The 4 poles on it's filter can be switched  
> from hipass to lopass to notch and each one has an offset control.  
> With just one pole offset from the others he got the resonance to  
> behave what he described as "like a 303." It was pronounced  
> resonance, but it did not self oscillate. I have always assumed  
> that this is the point of having a different cap on one pole. Is  
> this incorrect?
>
> Mark
>
>
>
>
>
> On Dec 26, 2008, at 2:36 PM, karl dalen wrote:
>
>> Did anyone figured out why Doug Curtis used such a (gm) difference  
>> between
>> the last transductor and the preceding 3 in his filters? Factors  
>> of 50,
>> 75 and 100 times can be found in his various designs.
>>
>> Reg
>> KD
>>
>>
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