TS9/SD-1 circuit questions

[grrrunge]

Hello Everyone!

I recently started a thread over at the freestompboxes website, but i didn't think it'd do any harm to ask here as well.
I want to write an article for my blog about the TS9/SD-1 circuit. It's supposed to be an in depth explanation of the circuit in noob language.

I need some information on how the tone control works. I've already read the tubescreamer anatomy over at geofex, and i watched Wampler's videos on youtube about the circuit.
My original thread over at freestompboxes is here, if you're interested: http://www.freestompboxes.org/viewtopic.php?f=11&t=12615