Uses an OpAmp and transistor. If you use a bipolar device such as the venerable 741, the output can't go lower than 2 volts above ground or higher than 2 volts below Vcc.
http://www.elexp.com/t_audio.htm
This is a four channel amplifier ideally suited for use with quadraphonic equipment such as a Sound Blaster Live card.
http://www.zen22142.zen.co.uk/Circuits/Audio/quad.htm
10W design by J. L. Linsley Hood
http://www.sound.au.com/jll_hood.htm
http://www.intio.or.jp/jf10zl/compamp.htm
http://www.mif.pg.gda.pl/homepages/tom/files/simp200W.gif
Uses type 5687 Dual Triodes.
http://www.geocities.com/TimesSquare/1965/pp5687.html
The LM12 is a power op amp capable of driving ±25V at ±10A while operating from ±30V supplies. The monolithic IC can deliver 80W of sine wave power into a 4 load with 0.01% distortion. Power bandwidth is 60 kHz.
http://www.national.com/pf/LM/LM12CL.html
http://www.reconnsworld.com/audio_cartridgeamp.html