[sdiy] CMOS Saw to Triangle Waveshaper

[Scott Gravenhorst]

http://linux6/RemoteWebsites/gte/TekLab_FatMan_WebSite/VCO_pwm_tri_suboctave.html

See the part of the schematic shaded with a blue background.

Made of one 4027, one 4069, and one 4066.

This one sends a noninverted and an inverted copy of the saw
signal into a CMOS analog mux.  The mux is operated by a 
4027 set up as a toggle flipflop and is clocked by René's
4069 VCO.

Because the saw is not perfect, neither is the triangle,
however, I observed a much more mellow sound (more sine
like) than (especially) a square wave as well as a 
sawtooth of the same frequency.  The high end sounds
very flutey.  Bass end is rather thunderous.  (c:

The imperfections manifest themselves as a spike at each 
signal reversal as well as some misalignment of the peaks.
I think that if I used 1% resistors for the input and 
feedbacks for the 2 gates run in linear mode, the 
misalignment would be diminished.

       A
\     /|\
 \ | / | \    etc.
  \|/     \
   V

I do not know if the circuit is original.  I'd guess it
is not, it's quite simple.  Perhaps someone here knows.

In my prototype, I push the muxed signal thru another
linear CMOS stage for some gain.  The way it distorts,
it splines the ramps and makes it look more sine like.
I'll have to see how far I can push that.  I wouldn't
mind a (near) sine output as well.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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