This is a "tube sounding" distortion with the ability to capture the sound of an heavy overloaded tube amp.(with a bit of imagination though!)
Due to the red led's and the two gain controls it's possible to get many variations of "tube distortion" characteristics!...Well, that's my opinion anyway! In this curcuit I've used TL072, but use whatever op-amps you've got!
Though it's the same circuit as the dual supplied circuit found in my Rack page,the sound of this single supplied unit is a bit differently! I've omited the tone control because I wanted to come up with a better one!

Modifications:
Yes,there are a few! You can change the clipping-diodes,on one stage,or on both stages.
Try 1N4148,1N914 or other types. Led's on the first stage, silicon diodes on the next stage.
Changing the bass-cut at the input stage(around the first op-amp) changes the sound. Choosing between 2,2microF and 220nF for C1 gives you a bass cut around 40Hz and 340Hz.
There are endless possibilities!