Variable ramp generator

[Curtin, Steven D (Steven)]

> > My idea was to generate a stable saw or triangle and shape it
> > using a switched gain circuit. I must say I tried to design such 
> > a circuit, but either I am too narrow minded or blind - I just
> > cannot come up with anything. I hope somebody invented this before
> > and would not mind to share. 
> 
> It's cool, sounds fm-ish. You can just x-fade the saw/tri out. If you've
> never 
> seen this on a scope, too bad. It's cool to look at. Freq won't change,
> just 
> the wave morphing saw/tri. This can be simulated by grabbing your saw and
> tri mixer knobs and twisting like mad in opposite directions.....:-)
> 
> A more reasonable approach is to use Juergen's pnp/ota x-fade scheme,
> two trannys and two otas and you're in business.Alternately the Serge wave
> shaper/multi also works well and it's even more simple. 
> 
I remember from the Gnome I built long ago that the transition from the saw
to the ramp sounded very much like pulse width modulation.  This was very
different than just crossfading from a triangle to a ramp.  One side-effect
of the circuit on the Gnome (at least on mine) was that the pitch would also
change a little bit when the shape knob was twiddled.  The Serge Dual
Universal Slope Generator could also do this, since it operates at both
audio and subaudio ranges.   Grant's Richter/Wiard's Envolator module might
also do this (Grant, does it operate at audio range?).  This would be a cool
circuit to add to the Fatman, since its 555 outputs a square wave. 

Steve C

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Steven Curtin  
Lucent Technologies Microelectronics
ph: (732)949-4404   fax: (732)949-6711
http://www.emf.org/subscribers/curtin/
sdcurtin at lucent.com
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