Adding to the info contained in this thread I add the Scots Guide to Electronics in particular the Audio analog section. This site contains easy to understand analog design concepts in a semi technical easy to understand language.
http://www.st-andrews.ac.uk/~www_pa/...io/Analog.html
the animated gif depicting the Class of amplifiers allows instant visulization of how this actualy works as a system
http://www.bcae1.com/ampclass.htm