[sdiy] SSM2040 vs CEM3320

Tom Wiltshire tom at electricdruid.net
Fri Nov 3 19:56:11 CET 2023


The CEM3320 has a VCA provided for CV-controlled resonance, but you can put a lot of stuff in front of it, and you can choose what signals you send to it, so you've got a lot of options in your design of feedback architecture. It is literally just an uncommitted VCA attached to the input. You could use it to give you a voltage-controlled mix of some external signal into the filter if you wanted - it doesn't have to be resonance.

A later chip like the CEM3328 closes down the options still further - that *does* make an explicit internal connection from output to input.

Tom


> On 3 Nov 2023, at 17:42, Michael E Caloroso via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> One of the other differences of SSM2040 and CEM3320 is that the 3320 includes integrated feedback circuit for VC'd resonance whereas the 2040 does not.  A 2040 designer is free to define the feedback architecture which is the biggest contributor to the resonance quality and sonority of a filter network.  With the 3320 (and succeeding SSM/CEM designs) you're stuck with the feedback architecture on the substrate.
> 
> Three problems of the 2040 design is 1) it is VERY sensitive to ESD, 2) the power rails MUST rise in synchrony on power up, and 3) it has no short circuit protection on the outputs of the gain cells.
> 
> MC
> 
> On Thu, Nov 2, 2023 at 10:54 AM René Schmitz <synth at schmitzbits.de <mailto:synth at schmitzbits.de>> wrote:
> Hi Mark,
> 
> Am 02.11.2023 um 14:10 schrieb mark verbos:
> > Don’t you mean 
> > https://patents.google.com/patent/US4514704A/en?inventor=Douglas+R.+Curtis <https://patents.google.com/patent/US4514704A/en?inventor=Douglas+R.+Curtis> ? 
> >
> >
> That is the "who the heck needs buffers?" filter as in CEM3372, and 
> possibly others.
> 
> 
> > I only say that because this is a filter and the one you posted is a 
> > “linear/logarithmic analog multiplier”
> > Anyway, cool stuff.
> >
> Hang a few caps to GND in strategic places and you get a filter. The 
> description of the cascade of four stages later in the patent is a 
> giveaway.
> 
> 
> Best,
> 
>   René
> 
> 
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