FM Sound Unit

From Sega Retro

FMSoundUnit 2.jpg
FM Sound Unit
Made for: Sega Mark III
Manufacturer: Sega
Type: Add-on
Release Date RRP Code
Sega Master System
¥6,8006,800[1] FM-70

The FM Sound Unit (FMサウンドユニット) is an add-on for the Sega Mark III used to enhance the sound output of certain Mark III games. It was sold in Japan beginning in 1987 for ¥6,800.


The FM Sound Unit contains a YM2413 FM synthesizer chip that acts in lieu of the built-in SN76489 PSG chip, featuring nine mono sound channels. It connects to the Mark III through the console's front expansion port, and also has a 5-pin DIN pigtail connector at the back which connects to the Mark III's AV out. Composite video and the final audio signal are then output from a 5-pin DIN connector on the rear of the unit. Those who wanted to have FM audio through an RF connection needed to connect the Telecon Pack's transmitter module to the FM Sound Unit, as FM audio is not passed through to the Mark III's RF modulator. Once connected, the unit sits on top of the left-hand side of the Mark III and hooks into the top air vents. It is not compatible with anything other than the Mark III.

When the redesigned Sega Master System hit the Japanese market, the FM Sound Unit was built-in to the console (though it is absent from international releases). The Japanese Master System also allowed for both PSG and FM audio to be mixed together, something not possible on the standalone FM Sound Unit. This is used to great effect in its special BIOS screen, which plays a rendition of the Space Harrier theme using both audio chips. However, no games were released that took advantage of this feature.

Unfortunately not all Mark III or Sega Master System games made use of FM audio, and Sega eventually stopped including FM audio support during 1989. The unit was not built into the Sega Mega Drive or Power Base Converter, so these extra features cannot be activated when playing Master System games on Sega's 16-bit console. Newer flash cartridges for the Mega Drive have the ability to emulate the YM2413[2], and there also exist modification boards[3] to allow for FM audio on non-Japanese consoles.


Note: Only the Japanese versions of Phantasy Star and Ys: The Vanished Omens have FM Sound Unit support, as the FM audio code was removed to make room for translated text in the international releases.

The following games have FM soundtracks but were not released in Japan:

Out of these, only Wonder Boy III is known to have been released in South Korea. However, the FM audio in Wonder Boy III will only function with a Japanese system equipped with FM audio capabilities; Western consoles modified with FM audio use PSG due to the game's region detection code. However, the Wii Virtual Console version allows using the FM audio.

Incompatible Games

Great Baseball (1985), Pit Pot and Teddy Boy Blues have control issues when the FM Sound Unit is connected, and Sega included a special notice with the add-on to let owners know of these compatibility issues. These games do not have problems on the Japanese Master System.

Physical scans

Master System, JP
FMSoundUnit SMS JP Box Front.jpg

Production credits

Developer mentions[4][5]

External links


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