[sdiy] They aren't sawtooths, they're ramps

[David G. Dixon]

This reminds me, I have now grafted the 2164 Expo onto the Thomas Henry
triangle-core VCO-1, and laid out a very tight PCB (2.1" x 5.5") with very
low parts count which also includes Ray Wilson's sine shaper (to use up the
extra 13700) and a variable sync.  Simulations suggest that the tracking
should be almost perfect, as it should be much easier to obtain excellent
tracking with the VCO-1 then with JFET-switched saw-cores.  Also, the Linear
FM is not inverting, which makes a nice change.

I'll try and build the prototype this weekend, then I can report back on how
it all worked out.

Incidentally, Ray Wilson's 13700-based sine shaper can achieve, at best,
THDs of about 1.3%, mostly because one can't get rid of the pointy tips.
The Thomas Henry's discrete sine shaper can achieve THDs as low as 0.6%.  At
least, that's what the simulations say, and my ears confirm this.  However,
I hate to see half a chip go to waste (I'm already wasting half the 2164).

Finally, a question:  The 13700-based sine shaper generates sine waves with
a slightly positive dc offset.  Is this something people generally live
with, or would one typically add a coupling cap to the output?  I'm hesitant
to do that myself, but I'd like to know the prevailing opinion.



> Suppose it's one of those orientation cases; same circuit, just not
> arranged in the side-by-side format, like in the TH VCO-1 schematic.
> 
> http://mypeoplepc.com/members/scottnoanh/sitebuildercontent/sitebuilderfil
> es/vco1_schem2.pdf
> 
> Still most of the time I just see high gain stages and/or clipping diodes
> though - have any examples that have a sine shaper in some configuration
> or another?