http://margo.student.utwente.nl/el/audio/pwramp02.gif
designed to be used as car amplifier.
http://home.maine.rr.com/randylinscott/may98.htm
and push-pull Amp.
http://www.recherche.enac.fr/~puechmor/e_aclass.html
http://www.sound.au.com/project10.htm
This circuit is the audio amp section for a complete optical transmitter. The circuit amplifies and filters the voice audio signals from an electret microphone
http://www.discovercircuits.com/PDF-FILES/voicex1.pdf
Low distortion amplifier using discrete components.
http://www.mitedu.freeserve.co.uk/Circuits/Audio/2wamp.html
http://sound.westhost.com/project72.htm
The about 660-mW output can be gotten with the 16-ohm speaker. The impedance (4-ohm and 8-ohm, and so on),
http://www.interq.or.jp/japan/se-inoue/e_ckt3.htm