[sdiy] LFO with variable waveshaping

[Don Tillman]

   > From: Tim Parkhurst <tparkhurst at siliconbandwidth.com>
   > Date: Tue, 26 Nov 2002 16:29:03 -0800
   > 
   > You might want to take a look at Don Tillman's idea at
   > 
   > http://www.till.com/articles/VariableSaw/index.html
   > 
   > Looks like an interesting circuit, but note that it is just a
   > proposal and Don hasn't tried it out yet (have you, Don?)

Not yet; my life has been way too busy.

Just a couple quick notes...  

There's a Moog patent for a variable duty cycle sawtooth LFO; check it
out on my web page of Moog patents:
  http://www.till.com/articles/moog/patents.html

Variable duty cycle sawtooths are actually pretty easy to implement --
for the frequency to stay constant while changing the slopes you need
to have the sum of the slope-up and slope-down times to be constant.
Which means that the sum of the inverses of the positive and negative
slope rates be constant.  And a single pot will do that just fine with
the ends connected to positive and negative reference voltages and the
wiper connected to the integrator opamp's negative input.

The interesting thing about my proposed circuit is that the duty cycle
is voltage controllable.  That's more difficult.

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com