I have an amplifier in my workshop, for listening to tunes from my iPod, but if I turn it up louder then whisper level, it distorts, pretty bad. I've been going nuts trying to figure it out, even tried many different speakers, from 1/2 watt to 20 watt ratings, and swapped out the LM386 chip. I have another one of these kits, used for an iPod amp around the house played through a 1 watt 2 inch speaker, plays fine, with little or no distortion at normal listening levels. This amp is run off 4 AA batteries, while the distorting one is run of a 9 volt battery.
Schematic: (Look at the amplifier section)