Some stuff is around the web, some is from other people. Particularly for classic kit, someone's usually analysed it before, but it's not always in a good tutorial kind of form. I did a lot of messing around with audio/programming from my early teens onwards, so I have a good intuition about how the maths and sound link up.

A lot of this stuff can be made from relatively simple building-blocks though, and you don't have to copy a previous configuration. My thought process was pretty much exactly as written in the blog-post! I just wanted to make something which didn't require any special tuning skills.