I wrote about this circuit sample here. Mark Hammer posted this over at DYStompboxes.com forum. I think it was probably meant for synthesizers. It looks a lot like the kinds of things people are doing with guitar pedals!
I used the Falstad circuit simulator to mock it up: Bernie Drive simulator.
The output doesn’t look crazy but it does have a bit of a tube like quality. Who knows its just a picture, we will have to hear to really make a judgment. The shape is asymmetrical, rounded on the bottom and sharper on the top. Might have even order harmonics.
I set the range of the op-amp to 0 to 9V, and created a bias voltage of 4.5V. The input is a sin wave of 1V peak to peak. This seems like the ranges we might see in a guitar pedal.
The input wave form is on the left, and output is on the right.
Add a 1M pot to control the gain. At the low gain the output, its hard to see here, has little distortion.
Turn up the gain a little and the wave form is symmetrical. More triangular than the input.
More gain and we get, what looks like some crossover distortion, along with the asymmetrical clipping.
The input is a little hot for a guitar, Lets try a smaller input signal. This shows some classic soft clipping.
Lets try a hotter input wave form. Imagine we added a an op-amp input buffer with a gain control. This with a 2V peak to peak input. The top half of the signal gets clipped.
This deserves to put on the breadboard for some experiments.