A conventional common-drain MOSFET-based power op amp, with a simple and stable configuration, has a dynamic response identical to that of IC1. However, as a power amplifier, it exhibits a limited-output voltage swing that is typically less than either supply by 6V.
http://www.edn.com/archives/1994/092994/20di5.htm
The circuit is based on a simple inductor-capacitor filter circuit, and needs only a pot and a small light bulb to set and stabilise the oscillation. The frequency is fixed, and with a good inductor should be capable of very low distortion.
http://sound.westhost.com/project59.htm
This App Note describes a digital amplifier, which operates from13.5-Volt power source and outputs up to20W poor channel power.
http://www.tripath.com/downloads/EB_TA2020.pdf
A power MOSFET is biased using a pot (needed to correct for different device characteristics) so that the voltage at the drain is about 1/2 the supply voltage.
http://sound.westhost.com/project36.htm
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
Based on the National Semiconductor LM3876. This device is capable of delivering as much as 56W of continuous average power into an eight ohm load with 0.1% THD from 20Hz to 20Khz.
http://www.web-ee.com/Schematics/45WattAmp/45W%20amp.htm
A simple amp to build, uses commonly available parts and is stable and reliable.
http://www.sound.au.com/project03.htm
circuit amplifies and filters the voice audio signals from an electret microphone.
http://www.imagineeringezine.com/PDF-FILES/voicex1.pdf
http://www.sound.au.com/project53.htm
Computer Audio Booster, 4-Transistor Amplifier for Small Speaker Applications, Op-Amp Audio Amplifier, Crystal Radio (and other purpose) Audio Amplifier, Class-A Audio Amplifiers
http://www.techlib.com/electronics/audioamps.html