[sdiy] Temperature Compensated Exponential ConverterUsingSSM2164

[David G. Dixon]

> I think you need to trim it since values varies and repeatability of a
> design needs to be achieved. Also, how do you repeatably achieve
> 0,2678345615807 V or whatever we crank out as the optimal voltage?

Yes.  What I was arguing was that the adjustment could be confined to one
trimmer, specifically, the one which gives the tempco voltage.  The
appropriate feedback resistance could simply be calculated and applied to
the nearest 0.1k.  I believe that I have demonstrated successfully that the
trimmed values are more or less insensitive to the VCA gain temperature
coefficient, and that the optimal feedback resistance at the expected value
of the VCA gain coefficient will still serve admirably for tempco even if
that gain coefficient is several percent off spec, which is highly unlikely
for 2164s.

Having said that, I also know that the effectiveness of the tempco relies on
coming within about +/- 250 microvolts of the optimum tempco voltage.  Even
being 1 mV away from the optimum puts the first octave about 0.25% out of
tune even at the reference temperature.  This extreme sensitivity is
probably the "Achilles' heel" of the design.  Drift in the supply voltage,
and even temperature sensitivity of the resistor and trimmer, could become
serious issues.