Where to start???

I have a mathematics degree so I have no issue understanding the math thats happening but I feel so lost trying to jump into understanding the math behind amp building.

Does anyone have any resources where you can start from the very basics (what is a transistor and how it works type stuff) and then build up to more complicated stuff. My goal is to understand it all well enough to build my own stuff and not rely on kits that tell me how to do everything. I'd love to really understand the math.

Thank you!