Gameboys: Prosound mod

The stock GB comes with both a headphone mini-jack and a small speaker. This is fine for playing games. However when it comes to recording audio from the headphone output, the signal is actually weak and noisy.

GB musician/hacker Trash80 is credited to have been the first to publish a modification where the audio is directly taken at the line source, before the headphone amplification. This much cleaner signal is then redirected to an external connection (mini-jack, jack, RCA, etc). This is what is called a Pro Sound mod.