[sdiy] Figureing out Buchla timbre waveshaper

[ASSI]

On Mittwoch, 16. November 2005 04:45, Aaron Lanterman wrote:
> What I'm still scratching my head on a bit is the nonlinearities,
> which have a structure like:
[...]
> However, with R2 where it is, if I apply my usual op amp rules, that
> puts the output at ground, which makes no sense. So this must be a
> case where I can't apply my usual op amp rules so I'm outside my
> comfort zone.

The deliberate placement of R2 tells you that the usual opamp rules 
don't apply. ;-)

Consider for a moment infinite impedance on the output, to fulfill the 
"rules" and make virtual ground at +, the current into R1 must equal 
the current through R2. Now if the resistor values are such that the 
current through R2 can't get large enough, once you go outside some 
input range the output isn't at ground anymore and follows the input at 
a distance (assuming the right amount of impedance past the output) 
like this (use fixed width font):

             /
            /
           /
   --------
  /
 /
/

I don't know the values of the resistors, but to me this indeed looks 
like a nonlinearity that could be used in a waveshaper.


Achim.
-- 
+<[Q+ Matrix-12 WAVE#46 Neuron microQkb Andromeda XTk sonic heaven]>+

Factory and User Sound Singles for Waldorf Q, microQ and rackAttack:
http://Stromeko.Synth.net/Downloads.html#WaldorfSounds