I've always sort of liked the classic "GE" tape head/mic preamp
circuit:
ftp://jjlarkin.lmi.net/GEcircuit.jpg
but it occurred to me that it might also make a nice headphone amp...
ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG
Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.
John