[sdiy] linearize OTA for VCF?

[UrosM]

Hi JH ( and the rest )

"jh." wrote:
> 
> > I was just thinking that since so many people seem to believe that the
> > distortion in the Moog ladder sounds good, why doesn't anyone talk about
> > distortion in OTA-based designs?
> 
> I did, so often that I hesitate to do it all again. Half of my
> SSM2040-related
> posts must be about distortion. I don't want to be a pain. (;->)
> 
> JH.

Actually , I found reference only in your first posting about 2040 
( after painful search trough archive ),

direct quote :

>> and here are some details that I think are 
>>important for the SSM2040 sound: 
>>(1) A minimum (for a ota/buffer filter) of pn junctions in the signal
>>path, 
>>due to a very minimalistic ota topology: the ota just consists of 
>>a differential pair and one single current mirror. 
>>(2) The very special distortion scheme, due to the same minimalistic 
>>ota topology: The ota output can only swing into the positive 
>>direction. The buffer is a npn darlington, so levels are shifted 
>>by approx. -1.4V, so you get a very unsymmetrical clipping 
>>at the output. This, together with the frequency-selective distortion 
>>of the ota-inputs, gives a very unique overdrive charactersitic. 

 OK , that's about distortion , but I found two more interesting
topics in archive during the search . First , you mentioned
experiments about using 3096 as OTA cell , but I haven't found any
conclusive report on that topic in archive . Second ( maybe even more
important ) you mentioned doing research on unmatched pairs in 2040
gm cells . Again , no more reference about that in archive . Do you
remember anything about these and what were the results ( compared
to your discrete matched version )?

regards
urosh

yeah , one more thing : does anyone know where any linearisation
scheme used inside 3320's gm cells ( since people hate to overdrive 
these things )?