Yamaha FM Sound Synthesizer Unit
This page was last modified 15:07, 16 December 2021 by Mars2000you. Based on work by Gdx and Alexey and others.



The FM Sound Synthesizer Unit is a module for the 60 pins side slot on the Yamaha CX and YIS computers: the CX series were only sold in music shops and the module was included with the computer, though also sold separately; the YIS series were available in the same shops as other MSX computers and generally sold without FM Sound Synthesizer Unit.

With a little adapter (UCN-01), the module can also be inserted into the cartridge slot of any other MSX computer. However, this adapter is not required on some computers released by Victor (HC-5 and HC-6) or Sakhr/Al Alamiah (AX-100 and AX-200), which were also manufactured by Yamaha.

Note that the SFG-05 module requires a computer with a minimum of 32kb RAM.


The FM Sound Synthesizer is built around the YM2151, also known as OPM (FM Operator Type-M) or YM2164 a.k.a. OPP (FM Operator Type P) sound chip. These IC's have 4 operators and are especially used in the cheaper Yamaha DX series (e.g. the DX9, FB-01), several arcade games and the Korg DS-8 and 707.

This unit includes a D/A converter (YM3012), so 8 audio tone signals can be obtained at the right and left channels. It has also a YM2148 chip with MIDI function and keyboard scan function.


There are several versions of this module:

  • The SFG-01 FM Sound Synthesizer Unit, released in 1983, is build around a YM2151 (OPM) sound chip and YM2148 MIDI UART.

It has a 16kB ROM (MBIOS 1.0) which can't receive external MIDI note information; it requires a proprietary keyboard (YK-01, YK-10 or YK-20) and it uses its MIDI port only as an output to send data to a digital synthesizer, for example the Yamaha DX7. (Note that it is technically capable of receiving MIDI data, just the ROM does not support it.)

  • The SFK-01 FM Sound Synthesizer Unit, released in 1983. It's same as SFG-01, but without MIDI connectors.
  • The SFG-05 FM Sound Synthesizer Unit II, released in 1984, is build around a YM2164 (OPP) sound chip and YM2148 MIDI UART.

It has a 32kB ROM (MBIOS 2.0) which supports MIDI input, so it allows the internal FM synth to be played by any external MIDI keyboard. Note that the YM2164 is compatible with and virtually identical to the YM2151.

SFG-01 and SFG-05 have 2 MIDI connectors (MIDI-IN and MIDI-OUT), 2 audio stereo connectors (L and R) and a music keyboard connector.

  • Later, SFG-05 clones were made by the RBSC, then reproduced by Omega.



SFG-01 module
SFG-01 module


SFK-01 module
SFK-01 module


SFG-05 module

SFG-05 clones

SFG-05 clone by the RBSC
SFG-05 clone by RBSC, produced by Omega
SFG-05 clone with adapter by RBSC

Launching of the firmware

From BASIC, the music firmware can be launched with CALL MUSIC or _MUSIC. If the module is used on a machine with MSX-MUSIC in a lower slot, you have to make the distinction between both extensions: to start the SFG firmware in this case, enter CALL MUSIC plus any additional letter or number (eg _MUSICA)

Note that on the MSX2+ Sanyo and Sony machines with built-in MSX-MUSIC, this ROM is in slot 3-3. The SFG-05 module can only be added into a lower numbered slot, therefore CALL MUSIC will always run the SFG firmware when this module is present (even with additional letter or number).


SFG-05 Voice menu (F3)

The module includes 46 pre-programmed 8-note polyphonic voices, plus a subset of the same voices in monophonic form, and 2 reserved voices: voice 47 is for use by the CSM (Composite Sinusoidal Modeling) vocal synthesis driver, voice 48 is for no voice.

When using the SFG-05 module, you can have the list by pressing F3. Voices 1 to 46 can be edited and modified by using specific cartridges: the Yamaha YRM-102 FM Voicing Program and YRM-502 FM Voicing Program II (the YRM-502 was also built in the CX5MII and CX7M-128 computers).

The SFG-05 module allows to have 48 system voices (internally 0 to 47) and 48 user voices (internally 64 to 111); the internal voice numbers 48 to 63 are reserved. To switch between the system voices and the user voices, press twice quickly the SELECT key.

Here's the complete list of system voices. When there are 2 instruments mentioned, the first one is for SFG-01 and the last one for SFG-05.

Voice Instrument Voice Instrument Voice Instrument
01 Brass 1 17 Piccolo 33 Train/Low Strings 1
02 Brass 2 18 Oboe 34 Ambulance/Horn Low
03 Trumpet 19 Clarinet 35 Tweet/Whistle
04 Strings 1 20 Glockenspiel 36 Raindrops/Storm
05 Strings 2 21 Vibraphone 37 Rhythmic Brass
06 Electric Piano 1 22 Xylophone 38 Rhythmic Flute
07 Electric Piano 2 23 Koto 39 Rhythmic Guitar
08 Electric Piano 3 24 Zitar/Zither 40 Rhythmic Horn
09 Guitar 25 Clavichord 41 Rhythmic Bass 1
10 Electric Bass 1 26 Harpsichord 42 Rhythmic Bass 2
11 Electric Bass 2 27 Bells 43 Snare Drum
12 Electric Organ 1 28 Harp 44 Cowbell/Round Cymbal
13 Electric Organ 2 29 Bell+Brass/Smadsyn 45 Percussion 1
14 Pipe Organ 1 30 Harmonica 46 Percussion 2
15 Pipe Organ 2 31 Steel Drum 47 (reserved)
16 Flute 32 Timpani 48 (reserved)