[sdiy] Temperature Compensated Exponential ConverterUsingSSM2164

[David G. Dixon]

> I dunno about your synths, but mine get pretty warm.
> I'd go all the way up to 50-60 degrees with my area of interest.

Well, "synths" is overstating it a bit.  I have exactly one synth, the
analog modular I've been building from scratch for the last few months, and
currently which consists of eight modules + two matrix scanning keyboards.
Each module has been designed to draw very little current (by using mostly
100k feedback resistors and 100k pots, small reference currents, digital
chips mostly 74HC CMOS, etc).  I don't notice any heat in the case when my
synth is on, even for extended periods.  I'd be scared to death if it ran at
50-60 deg C!  I was thinking that one might have it outside on a summer's
day....

In any case, this does not alter the basic argument I was making in my last
message.  Use the theoretically correct feedback resistor, tune with the
tempco voltage trimmer, and tempco should take care of itself.  Even if the
VCA gain coefficient is off a bit, it should still be superior to the
typical expo circuit.  If the synth typically runs hot, then the value of
the reference gain coefficient should be changed accordingly, along with the
feedback resistor value, and the synth should be warmed up before trimming
the tempco voltage.

(Of course, this is all contingent on actually trying it.)

> Bear in mind the whole VCO won't be the same temp - instead some parts
> will be hotter while others will be colder. Which means stuff doesn't
> extrapolate that easily.

How much current are you drawing through your VCO?!?