Here is a simple amplifier for boosting the audio level from low-power sound cards or other audio sources driving small speakers like toys or small transistor radios. The circuit will deliver about 2 watts as shown. The parts are not critical and substitutions will usually work. The two 2.2 ohm resistors may be replaced with one 3.9 ohm resistor in either emitter.source

This is a High Quality, simple design Stereo Preamplifier with Bass-boost.The circuit requires 20 to 30V supply.This preamplifier was designed to cope with CD players, tuners, tape recorders etc., source

This is 10W Audio Amplifier circuit with Bass-boost,High Quality, very simple design,No preamplifier required.This design is based on the 18 Watt Audio Amplifier, and was developed mainly to satisfy the requests of correspondents unable to locate the TLE2141C chip. It uses the widespread NE5532 Dual IC but, obviously, its power output will be comprised in the 9.5 - 11.5W range, as the supply rails cannot exceed ±18V.source