Can be directly connected to CD players, tuners and tape recorders.
http://www.electronics-lab.com/projects/audio/001/index.html
High Quality simple unit, No need for a preamplifier.
http://www.redcircuits.com//Page2.htm
The optimal supply voltage is around 50V, but this amp work from 30 to 60V.
http://www.electronics-lab.com/projects/audio/042/index.html
Uses TDA1554 Two Channel Audio Amplifier Chip
http://www.aaroncake.net/circuits/amp20w.htm