Recently, I built an audio amplifier based on TI's hybrid digital chipset. It is made mostly from recycled parts (the only parts I purchased just for it are the chipset, terminal block, and switchover relay). It is built in a case from an old 802.11b router and the power supply is from an old laptop. The chipset uses only 1W (one watt!) at normal listening levels. The power supply is actually quite efficient - level 3 efficiency rating. Here's the schematic:
And here's a view of the circuit boards:
P.S. I named it after a celebrity. Amanda Harris (
http://barbiebarbell.com/ ) is known for her incredible power-to-weight ratio and that's what first came to mind when I cranked up the volume (the chipset is capable of over 60W RMS continuous in my testing, which is *VERY LOUD*).