Sunday, November 4, 2012

Neat OpAmp Waveshaper

So I as messing around in LTSpice (what I use for running circuit simulations) and wondering what a passive Sallen-Key filter can do if you muck with the components. I used a square wave from a 9v-powered 555 oscillator circuit as the input and monitored the output.
Here's what I found. If frequencies look different, it's because I took pics of less oscillations. None of these actually change the frequency. Oh, and the resistor values are simulating a dual-ganged potentiometer.

Normal Setup (via Wikipedia):
Normal, with less input resistance:
Removing input feedback loop, 100k resistors:

Reducing input resistors to 10k:
And, because I found the difference between 10k and 100k fascinating, I tried 50k resistors, which created just a triangle wave with a slightly bent top, so I tried 20k:
As you can see, a 100k pot sweep can go from a triangle wave to a dirty saw wave. 
So, it seems that a Sallen Key Filter can make a better waveshaper base than a low pass filter base. Now I feel like building a simple device with two filter setups, with and without the feedback loop.


It's SCIence!

I swear, I'll have a really interesting hand made modular synth if I keep this up (and keep getting parts, of course)!
All it needs is CV capabilities... Oh, and a VCA would be helpful. LOL

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