A very small but good quality amplifier circuit that is also fairly cheap. It is based on TDA2002 which offers very low distrortion. Power should be 12-15 volt 1,2A. The amplifier frequency responce ranges from 40Hz to 15Khz. A good heatsink is required. At the input you can connect your mp3 player or your pc audio out etc.
The TDA2002 is a class B audio power amplifier in Pentawatt package designed for driving low impedance loads down to 1.6ohms. The device provides a high output current capability up to 3.5A, very low harmonic and cross-over distortion. In addition it offers very low number of external components, easy assembly with no electrical insulation requirement due to Pentawatt package, high reliability, with embended short circuit and thermal protection.