[sdiy] Problems with linearized SSI2164 ?

David G Dixon dixon at mail.ubc.ca
Thu Feb 14 09:53:38 CET 2019


Well, Ian and Neil, it worked perfectly for about, oh, I don't know, 4000
VCAs or so, with the V2164.  In any case, I always put 100pF in my own VCAs
using the V2164, and I can't really comment on why 22pF was substituted
because I don't know the reason.  However, all I do know is that the crummy
old Coolaudio 2164 copies worked just fine with 22pF, and the fancy new SSI
chips did not.  Lesson learned I guess.

As far as my "tone" I was mostly angry about Neil's smartass remark about
"screaming not a drop-in replacement" when that is in fact the whole point
of the SSI2164, and I typed hastily.  Apologies.



> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On 
> Behalf Of Ian Fritz
> Sent: Wednesday, February 13, 2019 6:28 PM
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Problems with linearized SSI2164 ?
> 
> Exactly.
> 
> There is an old saying hereabouts: "Weirdness is caused by hf 
> oscillations." This is obviously one of the first things to 
> consider in a situation like this. Especially when a change 
> has been made that reduces the stability by a factor of 5.
> 
> If you make a change in a design and it doesn't work 
> reliably, then guess what? You should change it back.
> 
> Ian
> 
> 
> On 2/13/2019 4:53 PM, Neil Johnson wrote:
> > Hi David,
> > 
> >  > The datasheet says (in large boldface type):
> >  >
> >  > "FEATURES: Improved Direct Replacement for SSM2164/V2164"
> >  >
> >  > So, the datasheet is literally screaming that it is a 
> direct replacement.
> >  > In my book, that means a drop-in replacement.
> > 
> > You can drop an SSI2164 into a properly designed circuit, 
> and it will 
> > likely work as-is, or with minimal tweaks.  But this is analogue 
> > electronics, not Lego.
> > 
> >  > In any case, I believe that the circuit Dan was using it in is 
> > exactly the  > one given by Phillip Gallo in the datasheet, and it 
> > ain't working.  That  > tells me that the ICs are defective.
> > 
> > In this case, no - the circuit as built by Intellijel was 
> not as Irwin 
> > or Gallo designed, as the loop compensation capacitor was 
> wrong but a 
> > factor of 5ish (22p vs. 100p).
> > 
> >  > 2) If the SSI2164 is NOT a drop in replacement for the 
> SSM2164 (or 
> > it's true  > drop-in replacement, the Coolaudio V2164), 
> then I would 
> > submit that it is  > the most facking useless IC in the history of 
> > ICs.  There are hundreds (if  > not thousands) of designs using the 
> > 2164, and if these all have to be  > changed, that's an 
> enormous cost 
> > and a major headache for all involved.
> > 
> > That is rather harsh and unfair when the circuit as built by 
> > Intellijel was not the one published by Irwin or Gallo.  Details 
> > matter, and when you get the details wrong, you don't get 
> the results 
> > you wanted.  To blame the chip vendor is churlish.
> > 
> >  > I suspect that this thread alone will cost SSI a major chunk of 
> > business, at  > least in the short term.  If it were me and I were 
> > reading this thread, I  > wouldn't touch these shitty ICs with a 
> > ten-foot pole.  Good job SSI!
> > 
> > Really, David, is that language necessary in a public forum?  The
> > SSI2164 is a great chip, packs a lot of useful functionality, is 
> > actively supported by the manufacturer (including a very detailed 
> > datasheet), who is actively engaging in the analogue synth 
> community, 
> > and is a definite improvement over the SSM2164.
> > 
> > But you're right about one thing: /Good job SSI!/
> > 
> > Cheers,
> > Neil
> > --
> > http://www.njohnson.co.uk
> > 
> > _______________________________________________
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> > Synth-diy at synth-diy.org
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> > 
> 
> --
> ijfritz.byethost4.com
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