CA3046 vs CA3086?

[Martin Czech]

> Thanks a lot for the information.
> I have a question regarding the Moog 921. 
> I have built the saw to triangle converter but I can't get the triagle wave 
> quite symmetrical. Also there is a glitch at the peak. 
> I have tried many different transistors (including the specified 2N3904) and 
> experimented with different resistor values, but that doesn't change the 
> waveform much.
> Do you know if a genuine Moog 921B has these problems with the triangle 
> waveform? If it does, it could be considered part of the "sound" and probably 
> should be left as is.
> 
> Best regards
> Jorgen Bergfors
> 
> P.S. by adding a 1n capacitor in series with a resistor between the base and 
> emitter of the first tranny, the glich can be reduced. But Moog didn't do this 
> -- at least it's not in the schematics.

Converting a saw to tri will always give a glitch at one peak, or to be
exact at the discharge slope of the saw. All designs are more or less
rectifiers.  If the saw discharges the rectifier has to jump imideately
to maintain the tri waveform, but this can't be done with infinite
speed.  A cap will lowpass-filter/slew-rate-limit the out, if it is
properly done it will make the glitch smaller. A small glicht right at
the tri peak is very difficult to hear, by the way.  I don't know the
exact 921B circuit from my head, but I suppose it is some kind of
differential stage design, one half for the positive saw portion and
the other for the negative. All circuits of this kind I know require
perfect symmetry i.e. matching for best tri symmetry. If you want
perfect symmetry you might be better of with an op-amp rectifier
design. In this case there are methods to make the glitch smaller :
schottky diodes, adaptive miller compensation cap.

But as you say: the not perfect waveform may well be part of the sound
at the lower frequency end...

m.c.

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