The preenfm family brings the old FM synthesis in small open-source modern DIY boxes



The 3 supported models are

  • preenfm2 with R5 PCB (7 years old)
  • preenfm2 with R6 PCB and 24 bits DAC (2020)
  • prenfm3 (2020)

Quick start doc for both preenfm

pfm2_qs                           pfm3_qs

Preenfm3 documentation  is in it’s github wiki here.

Preenfm2 documentation is still on this wordpress site. Click preenfm2 in the menu above.


They both share the following main FM engine (differences are detailed bellow) :

  • Several independent instruments (4 for preenfm2 and 6 for preenfm3).
  • Powerful arpeggiator (Mutable-Instruments opensource algorithm) per instrument.
    • 1 gate effect
    • 4 rapid access performance parameters
    • The 4 instruments can be saved all at the same time in combo presets.
    • Each instrument has its own modifiable midi channel. They can share the same for FAT multiple timbres notes.
    • 28 FM algorithms from 3 to 6 operators
    • preenfm2 : 1 effect Slot per instrument (chose among 32 filters such as LP, HP, formant, crusher…)
  • pfm2 has 8 voices with 6 operators / 14 voices with 3 operators FM algorithm.
    pfm3 has 16 voices what ever the number of operators is
    Each voices has:
    • 7 low frequency modulators (3 LFOs, 2 enveloppes, 2 step sequencers).
    • 12 matrix rows : 16 sources, 32 destination (LP, HP, gate, stereo, MI, attack…)
    • Arpeggiator, LFOs and step sequencers synchronizable on external midi clock or internal clock.
    • preenfm3 : Effect is per voice
  • Operator features:
    • 7 builtin waveforms + 6 user waveforms read from the usb drive.
    • Stereo panning (at the carrier operator level)
    • 8 envelope parameters per operator. Time and level for 4 envelope points.
  • Direct Scala scale file loading for microtonality. Up to 128 Scala scales selectable. pfm3 allows a different scala scale per instrument.
  • Modular Randomizer
  • Midi over USB
  • Custom bootloader to make firmware upgrade easy
  • USB powered
  • Comprehensive user interface. pfm2 has a 4×20 characters display, pfm3 has a 240×320 color TFT display.
  • Small, portable and easy to build

The preenfm3 in addition the the difference listed above provides

  • A built-in 6 voices sequencer (step mode and real time). More details here.
  • A mixer part. More details here.
    • The 6 instruments can use any of the 6 independant audio output (mono or stereo)
    • Microtonal scale per instrument.
    • Midi split and filter per instrument


Mac/Linux/Windows open-source preset Editor : standalone and VST / AudioUnit

Here is the github repo for this editor.

preenfm2 Editor       preenfm2 Editor


Firmwares and editors are all open-source.



Last remark

Preenfm can import and convert DX7 sysex banks (just put them on the usb stick), but don’t expect the same DX7 sound.
Preenfm and DX7 engines are very (VERY !!!!) different, and important the DX7 banks is just an attempt to match DX7 parameters to preenfm2 parameters.
Consider this as a starting point to create rich modulated stereo preenfm sounds :)