Diodes in distortion box signal path

[sbirkenstock]

Hi Everybody,

I can´t figure out what the diodes are doing in the signal path of the jfetvulcan:

http://diystompboxes.com/analogalchemy/sch/jfetvulcan.html

Do they create distortion or is their purpose a protecting kind?

If they create distortion, how does it work in this schematic?

Best regards,

Stephan

[robthequiet]

I found a clue, here is a post from the designer:

Some ideas about tube amp and emulation/simulation, Joe Davisson

There are a few videos on youtube if you have not already seen them. It's a great pedal.