JoMoX Mod FM is a complete 8-voice FM synthesizer in eurorack format that promises enormously powerful sounds out of the box without forgoing the usual CV modulation options. Mod FM has 4 operators and 2 LFOs/VCOs per voice as well as 2 analog filters per voice and analog VCAs, which give Mod FM analog depth and warmth even though the FM engine is digital.

  • 8-voice fully multitimbral FM synth
  • 4 operators per voice
  • Full modulation matrix with 26 algorithms
  • 2 LFOs per voice that can also be used as VCOs
  • CV/gate per voice
  • CV modulation inputs per operator
  • Outputs for each voice plus mix output
  • True audio FM modulation inputs
  • True analog filters per voice
  • 24db low pass filter
  • 12dB multimode filter with continuous LP/BP/HP
  • True analog VCAs per voice
  • MIDI TRS type A
  • USB-C device
  • Digital reverb and 2 × stereo delay
  • Full patch storage including CV amounts
  • 128 presets, 118 multi sets
  • 2 128×64px OLED displays

Each voice has its own CV/gate inputs and an individual output. There's a stereo mix output where the even and odd voices are distributed and where internal effects such as delay and reverb can be mixed in. In addition to the CV/gate control, Mod FM has MIDI in and out in 1/8" TRS Type A format and a USB-C port that also processes MIDI. This allows you to create great metallic-sounding FM sounds and crisp basses, but also soft and deep-sounding analog sounds without much modular effort. Mod FM also offers numerous external CV modulations, for example to modulate each operator individually or to control the FM envelopes.

Mod FM is also fully multitimbral, meaning each voice can have its own sound in Multi Mode, which is also saved as such in the Multi Set. Here we come to the biggest advantage of the hybrid approach: modular can become a trap with complex sounds and FM itself is inherently complex, making it difficult to get the same great sound from before again, so Mod FM's ability to save and recall presets certainly helps!

Matrix FM

4 operators are arranged in a matrix in which each operator (sine oscillator) can be frequency modulated by the other three. The 16 endless controls in the matrix each set the modulation value (FM amount). Each operator can have its basic frequency adjusted individually (diagonal controls). There are various overtone modes that determine whether an operator is controlled by the keynote (CV / base operator) or locks in as an overtone (overtone operator) on the assigned base operator. Then the number determines the nth overtone or harmonic above the base operator fundamental frequency. The Overtone operator follows the Base operator, but can also freely modulate or be modulated. Each operator has an ADSR volume envelope. This envelope can also frequency modulate the operator.


The well-known algorithms from FM synthesis are actually special cases of the entire matrix, and since unmanageable feedback occurs very quickly if you change all the values ​​of the matrix JoMoX has implemented the algorithms. There are 26 algorithms that are based on the 4-operator DX9. There is also the option to enter the frequency of an operator in full Hz, but these are then fixed and can no longer be changed via the keynote, only through modulation – useful for percussive sounds.


Each voice has 2 LFOs, each of which can modulate the frequency (FM) or amplitude (AM) of an operator. Each LFO has 64 different waveforms, which are shown on the right-hand display. There is also a feature where each LFO can be switched to a VCO that can also be fed directly into the signal path and responds to the keynote; the original LFO rate becomes the detune. This means you can also create classic-sounding square/sawtooth analog basses or string pads.


Each voice has an analog filter, which is implemented using the SSI2140 chip from Sound Semiconductor, which in turn is based on the old SSM SSM2040 filters that were often used in Oberheim synths and the first Sequential Prophet 5 in the 1980s. The filter has a 24dB low pass output and a 12dB state-variable multimode filter, the characteristics of which can be continuously blended from low pass to band pass to high pass. Both filter types can be mixed independently of each other. The ADSR for the filter is fast and takes effect directly; the resonance is easily adjustable. The filter has its own dedicated cutoff LFO independent from the LFOs in the digital sound engine and also has 64 waveforms.


The VCA is a fast transistor VCA, which is important for snappy sounds and is featured in all JoMoX drum products. As a result, Mod FM can also be used as a rich sound source for techno drums and percussion of all kinds.

Metal noise

There is another sound source on the analog board: metal noise. This can be mixed into the filter independently from the FM synth digital sound engine and in turn offers an inexhaustible source of 'stark' sounds.


Mod FM also offers 2 effects – reverb and two delays – that work exclusively on the mix output. The delay can be beat-synchronized and offers the option of setting very short delay times in the millisecond range. This can be used to create very nice 'oil can' sounds and flanging effects.

ConditionBrand New (New)
Brand New items are sold by an authorized dealer or original builder and include all original packaging.Learn more
  • Mod FM
  • 2023
Synth Module Function
  • Full Voice Synth

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Kraft Music

Franklin, WI, United States
Joined Reverb:2016

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