Via the ‘Other Instruments & Toys’ page:
I stuck an LTC1799 oscillator module in a lil box which can be connected up to the gameboy via 1/8" stereo cable for variable speed under/overclocking. I really didn’t want to add any ugly controls to the Gameboy itself, so this worked out well. It runs like normal without it plugged in, but with it plugged in you're able to use coarse and fine control knobs to drop it to a near-stop at 100Khz, or speed it up to 7.12Mhz (original gameboys run at 4.19Mhz). It crashes any higher than that, so I capped the speed there (though the 1799 does go up to 33Mhz). Also added a switch to set the max speed at either 1x or 1.7x, so in a performance setting there's no need to fumble around for the proper speed after dropping it down. Fun for music, also a quality of life improvement for the Pokemon grind. This gameboy has been a nice restoration project, and has a few other mods as well (Backlight, bivert chip, internal pro-sound mod, internal speaker amplifier, glass screen cover).
Check the photo gallery for a wiring diagram! The 1799 module I used came from Amazon, though any will work.
August, 2020.