Delton T Horn's Music Synthesizers a manual of design and construction. http://lucmorton.com/lucstuf/pdf/Music%20Synthesizers%20-%20...
Miller Puckette's theory and technique of electronic music http://msp.ucsd.edu/techniques.htm
Dave Bensons music a mathematical offering: https://homepages.abdn.ac.uk/d.j.benson/pages/html/maths-mus...
Here is a list of other good reference books: https://sdiy.info/wiki/Synth_DIY_books Also, if you don't mind digital - have you seen the daisy ecosystem?
https://www.electro-smith.com/ https://github.com/electro-smith/DaisyWiki/wiki
They have built a DSP library with a lot of the basics, there are plenty of example projects, and a supportive community.
https://github.com/electro-smith/DaisyExamples https://forum.electro-smith.com/