easy to build general purpose 50 watt amp
http://www.aaroncake.net/circuits/amp50w.htm
circuit amplifies and filters the voice audio signals from an electret microphone.
http://www.imagineeringezine.com/PDF-FILES/voicex1.pdf
uses a switched capacitor filter IC from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio.
http://www.imagineeringezine.com/PDF-FILES/3kscfamp.pdf
A simple amp to build, uses commonly available parts and is stable and reliable.
http://www.sound.au.com/project03.htm
tube amps and music electronics.
http://www.firebottle.com/ampage/
Two high gain amplifiers for adding audio to many projects.
http://www.wenzel.com/pdffiles/audioamp.pdf
based on TDA2030.
http://www.mitedu.freeserve.co.uk/Circuits/Audio/tda8.htm
Simple stereo amplifier based on TDA1554, can be used as a booster in a car audio system, an amp for satellite speakers in a surround sound or home theater system, or as an amp for computer speakers.
http://www.aaroncake.net/circuits/amp20w.htm