Whilst creating my Pokemon Yellow SNES cart, I noticed that the music sounded a bit strange, but not enough to immediately cause concern – once I compared it to the original played on a GameBoy, I was sure I had made a mistake connecting stuff up – the sound was just too high pitched, and even the gameplay felt slightly off. In fact, it turns out that the speed of the clock isn’t exactly the same as the original Gameboy – this is due to the Super Game Boy (SGB) using a value derived from the clock speed of the SNES itself, rather than its own internal one:
The original Super Game Boy is known to play the game program and its audio 2.4% faster than other Game Boy hardware. This is due to the use of the Super NES’s clock speed divided by 5, which ends up being 4.295 MHz instead of 4.194 MHz. The timing issue can be rectified by adding an appropriate crystal to the Super Game Boy and disconnecting the Super NES’s clock source.
Here’s a YouTube video highlighting the difference in speed between the two. This issue has been fixed in the Super Game Boy 2, however these were only released in Japan and are normally quite difficult to find for a reasonable price (at least in the UK!). Knowing this, I got to work modifying my SGB to run at the right speed. Required components are as follows:
- Super GameBoy cartridge.
- Small Gamebit screwdriver.
- Small Philips Screwdriver.
- 1x 4.194304 MHz Crystal Oscillator.
- 2x 15-33pf Capacitors (I used caps with a value of 22 picofarads).
- 1x 1M Ohm Resistor.
- Kynar wire for connecting the components to the SGB PCB – this is helpful as the pins on the SGB-CPU1 are very small. I used some light equipment wire from Maplin for the ground connection as it was a different colour, but Kynar should work fine as well.
- Hot glue and/or electrical tape for securing everything together.
- (optional) Small piece of Strip/Breadboard to assemble components on. You could also solder them directly onto the SGB PCB, but this puts more pressure on the chip legs, and we don’t want them breaking off!