[sdiy] Triple Lockhart cascade (while we're on the subject of waveshaping...)

[Aaron Lanterman]

I got curious what would happen if you cascaded a few of these. Here  
is what LT spice says:

users.ece.gatech.edu/~lanterma/triple_lockhart.png

Output of 1st stage is green, second stage is deep blue, output of  
third stage is light blue.

I picked the 30K/10K ratios of the first two inverting op amp stages  
to get a gain of 3; Ken's website said the Lockhart folder wants a +/-  
1.2V signal and gives out a +/- 0.4 V signal. That's how I got the  
number of 3. I boosted the feedback resistor of the last stage by 5 so  
it would look more like a usable output signal, but I don't show the  
output of that (it's just a gain).

I didn't get what I expected. One Lockhart stage gives one fold. But  
two gives four, and three gives... whoa, 13!!! How is that happening?

Someone wanna breadboard this up and tell me how it sounds? :)

Here's the LT Spice file if anyone wants to play around with it:

users.ece.gatech.edu/~lanterma/lockhart3.asc

- Aaron

P.S. I found that the Lockhart stage needs to see that 10K impedance  
at the output of the transistor stage to work right. If you don't  
include it, and you have it feeding infinite impedance, then the  
wavefold happens essentially instantly once you get to either side of  
ground.