Tempco Source/Analog vs Digital DIY

[Ingo Debus]

Paul Perry wrote:
> 
> At 05:38 PM 13/05/98 +0200, Ingo wrote:
> 
> >I heard about a synth that used an 8 bit D/A generating the reference
> >voltage for another (multiplying) 8 bit D/A. The first D/A selected a
> >pitch range (an octave for instance, don't know how large the range
> >actually was) while the other one does the fine tuning.
> >This synth was the "tiracon 6V".
> >
> this may be a flawed approach, as the precision of the first D/A can
> generate enough error to wreck the overall precision..
> it is OK if what you want is to add pitchbend, though.

I just had another look at the service manual of the tiracon and I must
confess I was quite wrong concerning the D/A. (This old GDR stuff is
hard to read, I'm from western Germany, it's almost a foreign language
;-)).
There is only *one* D/A converter, but it has 12 bit. There is a range
switching circuit for the VCO frequency cv, with a *1 and a *8 range. In
the VCOs there are no analog exponentiators. Somehow the frequency range
must have been covered with sufficient precision, maybe using an
autotune function.
And yes, Pitch Bend and VCO modulation is achieved by altering the D/A
reference voltage.

Ingo