Homebrew USB condensor mic inside an Altoids tin
In this instructable, a 15 year old kid Angelo describes a homebrew USB condenser microphone for recording quality audio at home. His project uses an USB soundcard (DAC), a transistor preamp circuit, and two microphones, all enclosed inside an Altoids tin box. The resulting setup has cardioid pickup pattern, smooth frequency response and 16-bit output, and 44.1/48kHz resolution, which gives you professional audio results under the budget of $10.
Homebrew USB microphone