• 12hp / 25mm deep / 150mA +12V / 120mA -12V
  • Analog stereo filter with digital control.
  • 4 pole stereo / 8 pole mono
  • Traditional filter ui with cutoff, bipolar FM, resonance, mode controls with CV.
  • Analog CV for FM and 1V/oct.
  • Pole control.
  • Variable character control with five classic characters: Fat, Crisp, Liquid, Sour and Mean.
  • Stereo control for inducing drift and offset for widening mono into wide stereo image.
  • Drive control with a boost function to overdrive the filter by 20dB.
  • Firmware updates via audio.
  • Two user banks and character upload via audio coming in further firmware updates.

The Neutron Flux 8 Pole Variable Character Filter is a 12hp skiff friendly Eurorack filter module with a stereo analog core and digital control over it. The digital control allows the core to shaped almost endlessly, taking on the character of almost any classic filter, and gives the filter the ability to explore sounds that have never been heard before.

Two 4 pole filter cores: These can be run in stereo, mono divided to stereo or chained as a 8 pole mono filter for almost LPG-like steep slope.

Characters: The green factory character bank has five characters with vintage spirit:

  • Fat – Our take on a ladderish filter character, great for slightly overdriven bass sounds.
  • Crisp – A bright state variable filter. Has a notch setting in the center of the mode pot.
  • Liquid – Spacey resonance. Filter pings dripping with dew.
  • Sour – The squelchy acid thing. Chained pole settings have a sour filter first and a flat distortion after.
  • Mean – This is all about bad behavior with distortion. Highly unstable.

The Yellow factory bank contains some more specialized characters. See Character Guide below.

Coming later in a firmware update the yellow and red bank characters can be replaced via audio update.

Overdrive: Long press on the pole switch enables the boost circuit. It is a +20dB before the filter core. Most of the audible distortion happens on the first filter stages which go from clean via warm saturation to hard distortion. In all cases the drive pot acts as a volume pot, while the overdrive function switches two different ranges.

The topology of the Neutron Flux allows toggling the boost separately for each core. For example some special characters could have the boost operating between the cores when they are chained in the 6 or 8 pole modes. See the Sour character for a use case like this.

Stereo: This control spreads the cutoff between L and R channels and induces VCO-like drift. This way a mono signal can be split into wide stereo. The stereo effect isn’t like a micro delay or chorus but something else. It’s more like an animated binaural mismatched eq-like effect. A sole static cutoff spread between left and right is a bit troublesome because the stereo image would be crooked. This is why we added some VCO-like drift in the stereo function. You can use it as set-and-forget way or apply it on top of an single envelope or LFO in the CV input. This way the modulator’s effect is applied a bit differently to each side.

Another special function in some characters is that the center point in the stereo pot is the zero spot. Move it to one side and the other moves in the other way the same amount. This way the filter can do some cool symmetric stereo phaser effects.

Neutron Flux on ModularGrid

Neutron Flux 1.2 Quick Start Guide

Firmware updates

You can update your Neutron Flux Filter’s firmware by holding BUTTON and POLES buttons and turning the power on. The module then enters bootloader state. Next, two different patterns are shown on the LED ring around CHARACTER. The second shows the version number (displayed below with each version). Don’t mind the first pattern, it is for our debugging purposes. After that the module is waiting for the firmware update. You can connect your computer or phone’s headphone output to CHARACTER jack and play the firmware audio file. The progress is shown on the voices LED array. After updating the firmware the module enters play mode.

From an ordinary headphone output on a smartphone, volume should be turned way up to achieve proper result. If a red animated pattern is shown, cycle power, go to the bootloader state and try again. WARNING: the audio files below contain 56k modem-esque DAMN LOUD audio. Don’t damage your ears or audio equipment with it.

When the module is waiting for the update files, the yellow LEDs show the input level. Try to run the audio via a VCA or an amplifier module if the level is not sufficient. The update may require multiple attempts. Check that the file has completely downloaded.




Neutron Flux Firmware 1.2

Firmware 1.2 LED Pattern

  • Yellow character bank is added, see bank description sheet for new responses. Banks are switched by holding “BUTTON” until character LED color changes
  • Increase character, mode, resonance and stereo CV -update rate to 4kHz
  • Reduce noise when  “CHARACTER” is between the named positions. Reduces Character CV effective bandwidth to about 600Hz
  • Increase Liquid 2 pole maximum cutoff
  • Swap left and right channels in Fat 1 and 3 pole modes, such that right channel is always the “master” channel which has resonance enabled.
  • Change pole selection pattern to “traffic light”, i.e. order is now 2, 4, 1, 3, 6, 8

Firmware 1.2 audio file direct download link

Neutron Flux Firmware 1.1

Firmware 1.1 LED Pattern

Internal release, no user observable changes

Firmware 1.1 audio file direct download link

Other useful info


 This project is a part of R&D project funded by European Regional Development Fund and European Social Fund.

Timo & Heikki’s Dev Corner

We’ll keep a small diary here what we’re currently working on

07.04.2021 – The Firmware 1.2 is released!