A couple of resources if you aren't aware:
Elliot Sound Labs is a hi fi enthusiast site with lots of circuits, theory and discussion.
https://sound-au.com/. They have a great set of tutorials and articles that are free to access. They take donations if you find it useful. I donate each time I use it because I find it so good. There is a lot of wisdom here.
Douglas Self has written a lot of very good books and articles on Audio Design over the years. He wrote a bunch of stuff for wireless world in the UK . He has also written several good books and anthology type collections- highly recommended. Nice style of expaining.
Baxandall is another old author, who collaborated with Self on some books. Less prolific than Self, but some very good stuff- "inventor" of the standard tone control circuit.
One thing to be a bit careful of when reading old references is to make sure some of the wisdom is still current. Power devices have improved immeasurably over the past couple of decades. "Linear" type MOSFET's are also less common these days- most are designed for switching with fast saturated switching rather than operating class A, etc. Some judgement required.
Have fun.