AW(2): Tri 2 Sin

[Martin Czech]

> 	> information about temperature compensation. Have you ever testet
> the
> 	> above mentioned 3080 converter at different module case
> temperatures ?
> 	> Say Tj=10C (winter situation) and Tj=50C (summer). If the
> differential
> 	> stage is heated up, it should appear that it is more overdriven,
> ie.
> 	> if you adjust the triangle amplitude at Tj=30C for minimum
> distortion
> 	> it may well be that at Tj=50C the sine output has a lot more
> 	> distortion. 
> 
> Good point. I have seen 3080-based VCOs which compensated for the
> temperature dependence of transconductance with diodes used to set the
> comparator's threshold voltage. Temperature compensation for the frequency,
> and a temperature dependent triangle amplitude. Perfect fit for the
> following
> 3080-based sine shaper ...

Yes, I remember now, it is the Harris app. note with 3080 comparator
and some diodes for the level. I just thought that this is a cheap
way for getting a reference voltage, sometimes I'm really blind!

But I think that a variable amplitude in generall is no good solution,
it could cause trouble in other converters, like tri2saw, or external
converters which don't share the same temperature.

> 
> 
> 	>And last but not least: is any loadspeaker capable to reproduce a
> sine
> 	>wave as such? Not mine! From this point of view it is a good
> quiestion
> 	>how much distortion of a "sine" wave can be tolerated.
> 
> Don't know. My headphones definitely monitor the difference of a sine
> from a waveshaper and a sine from an oscillating 4pole filter.
> 
Of course, headphones are much better because the membrane doesn't move much.
But at high volume they too will add very noticeable distortion, but wait...
it could well be that the human ear gets nonlinear, too.
If you think about "difference tones" (ie. if two pure sinewaves are played
you also hear the difference frequency, the sum will "drown" in the ear's
own distortion harmonics and intermodulation products).

If you look at it this way - the psycho acoustic way - a sine wave is 
an illusion, it just doesn't exist.

By the way:

My proposal for ranking of sine converters:

Bad 
-2 antiparallel diodes (Formant VCO)
-simple diff amp (3080 etc.)
-single stage with resistor between emitters (1496 etc.)
-10 diodes feedback network (need matching, Formant VCLFO)
-quad diff amp
-2*N diodes network a la Tietze/Schenk (temperatur compensated, not
 very sensitive to diode characteristics)
-AD639
Good

m.c.

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