YAMAHA DX7
YAMAHA DX7 is the first model of the DX series.
DX7 uses 16-polyphonic, 6-OP-Sine-Waves FM OPS chip, and the 4-OP synths can be seen as its simplified version.
YAMAHA DX7 (1983)
YAMAHA DX9 is the first 4-OP FM synth. It's the direct descendent, or a cut-down model of DX7. It retains 16-polyphony, with the 2 operators and velocity omitted.
YAMAHA DX9 (1983)
YAMAHA DX27 and DX100 are the second generation 4-OP FM synths with OPM chip. They are 8-polyphonic.
There was also DX27S, a version with built-in speakers and analog chorus. DX21 and DX27S are the only DX synths that has analog chorus.
The parameters (EG steps, frequency/detune settings, etc.) became more simplified than DX9, but velocity parameter is added, though the keys are not velocity-sensitive.
Since this OPM series, YAMAHA implemented louder modulator output for 4-OP FM than 6-OP. This feature compensates the lost operators, and makes it possible to generate impressive harmonics, in spite of the simplified engine.
YAMAHA DX100 (1985)
DX21 uses OPP chip, the multi-timbral version of the OPM. While OPP is 8-part multi-timbral, DX21 only uses the timbres as 2 sets of 4 voices parts.
The first synths that used OPP chip seem to be YAMAHA SFG-01 FM Sound Synthesizer Unit for their MSX computer YAMAHA CX5M series. Later SFG-05 came out with the velocity-sensitive firmware.
YAMAHA FB-01 is the half-rack version of OPP FM synth. It's 8-part multi-timbral.
YAMAHA CX5M series (1984)
The parameters are slightly different from DX21 series - it's closer to SFG series. Some parameters are added - velocity modulation for attack rate, etc.
YAMAHA also used OPP chip for Portasounds. The DSR series are the versions with synthetic editability, multi-timbrality and a PCM drum machine. Like CASIO HT-3000 and HT-6000, they can be seen as the workstation-synth versions of the family keyboard.
YAMAHA FB-01 (1985)
The high-end model DSR-2000 has velocity and the following 15 synthetic parameters are editable. This editing interface seems to be what precedented the Quick Edit interface of DX11.
Spectrum
YAMAHA DSR2000 (1988)
The third generation of the 4-OP synths use OPZ chip. In OPZ, Operators have more complex parameters than OPM/OPP. 8 basic waveforms including Sine, Operator Frequency Fine, Fixed Frequency Mode, etc. are added. OPZ can generate much more complex harmonics than OPM/OPP's sine waves FM. YAMAHA TX81Z is the first rackmount OPZ synth.
DX11 is the keyboard version of TX81Z with Quick Edit interface.
YAMAHA TX81Z (1986)
Quick Edit controls several parameters at once - For example, Brilliance parameter controls all modulators with relative change. This seems to be the first attempt of the feature, which is inherited in many synths today.
OPZ was also used in various products, such as the entry model synthesizer YS200, Wind Synthesizer module WT11, etc.
YAMAHA V50 uses the updated version, OPZII. The polyphony is doubled to 16, and much lower fixed frequency mode is added. It's my impression that V50 sounds closer to TX802 / DX7II than TX81Z, and I suspect V50 / OPZII may be the 16-bit version of 4-OP synths.
YAMAHA V50 (1989)
KORG DS-8 is the versions of FB-01 with quasi-analog editing interface and a digital delay unit. KORG 707 is the version without FX.
ELKA, the former company of Generalmusic - GEM, released some FM synths like EK44, using FB-01 compatible engine.
KORG DS-8 (1987)
QUASIMIDI QUASAR's MASS engine (Multi Algorithm Sound Synthesis) uses PCM, 4-OP FM and additive synthesis. But it's not deeply editable and the detail is unknown.
Many PC sound cards used 4-OP FM chips. IBM Music Feature Card can be seen as a version of FB-01 / OPP.
QUASIMIDI QUASAR (1994)
IBM Music Feature Card (1987)
YAMAHA provides many sound chips for mobile phones, and they still use 4-OP FM. The recent chip MA-7 (YMU786) uses 128-polyphonic 4-OP FM synth with other synthesis engines (PCM, streaming PCM, AL - Analog Lite, HV - Humanoid Voice, Multi-Effects, etc.)
YAMAHA MA-7 (2005)
Among many FM softsynths, Nativeinstruments FM7 and Disco DSP Phantom are patch compatible with DX21 and other 4-OP FM synths.
There are some hardware synths that can emulate 4-OP FM - Clavia NordLead 2 and KORG Z1, etc. Creamware SCOPE platform with the PCI DSP board has several FM synth applications.
Nativeinstruments FM7 (2001)
Disco DSP Phantom
KORG Z1 (1997)
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DX21
Deep Synthesis: Home7. 4. 2005