The SY77 was my second synth, bought back in 1990. It later got expanded by a PCM.EX by Musitronics. Some day I may need to score an SY99 for better FX and writeable sample memory. Some years later, I also got a TX16W for cheap (€70, call me lucky) and a nearly fully equipped EX5 (it's only missing the digital I/O) for less than 3x the price of that TX16W ...

I'll upload bits and pieces of information about those machines here as time allows.

Suggestions, questions, acclamation, or simply curiosity about who that guy is you might want to place here:

rainer@buchty.net

To fight spam, I'm running a combination of DNS and reverse-DNS checking and RBL-based filtering, so if your ISP's mail server is blacklisted or doesn't play according to the SMTP RFC, you might encounter bounces.

On one hand, the SY77/99 architecture is amazingly well documented:

• Solid manual,
• pretty exhaustive MIDI documentation, and
• of course — as usual — officially available schematics.

On the other hand, Yamaha liked to keep certain things cryptic — like the elusive "free algorithm" aka Algorithm 127.

Also, the OS is partly hidden inside the main CPU, a microcontroller with internal memory.

Inspired by Ken Shirrif's amazing blog series on reverse-engineering the DX7, I felt the urge to fill in some blanks regarding the SY77/99.

SY77

• Service Manual
  (on SynthZone)
• MIDI Implementation
  (on de.yamaha.com)

SY99

• Service Manual
  (on archive.org; PDF with text)
• MIDI Implementation
  (on usa.yamaha.com)

• It takes a brave soul like Oliver "Musitronics" Schwarz to desolder the ROM containing the upper half of the OS, to place a NOP-buffered read-out routine there that reads the H8-internal part of the OS to be sent out via MIDI.

  Do you feel brave enough? ;)
  (Happy to write the code for you.)

• The inner workings of Algorithm 127.
• How to get 16 Operator Waves from just one sine segment.

• Main CPU (Hitachi H8/532)
• Patent US5076133 describing the FM engine
• Patent US5383386 describing the AWM2 engine
• Patents US5380950 and particularly US5583309 describing the digital filter
• Patent US5365467 seems to describe the DSP unit (but there's a ton more Yamaha DSP patents)