Funkstill Filter Threek 13700, Analog Morphing Multimode Filter For Eurorack

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Funkstill Filter Threek 13700 is an analog morphing filter module with 12 available operation modes, a built-in matrix, and a very characterful sound.

Switzerland is known for its mountains and good cheeses, among other things. However, they can also create lovely Synthesizer products. Last year, I showed you in a video from Zurich Modular Fest the Kosmonaut analog Synthesizer from an indie developer. This year, Arie from Funkstill was on the festival and showed me his Filter Threek 13700 Eurorack module. It has been on the market since 2018, but it is an exciting module that many do not yet know.

The Filter Threek 13700 is an OTA-based analog multimode filter that offers two serial linked multimode circuits. The first can be operated in a high pass, bandpass, lowpass, or all-pass mode with a slope of -12dB per octave. The second filter circuit is a high-pass or lowpass circuit with a slope of -6 dB per octave.

Funkstill Filter Threek 13700

What makes this analog filter very versatile is the possibility to combine both stages with which you can make complex filter shapes. The following operation modes (combinations) are available.

Operation Modes

  • 3 pole output:
    • 3LP: Low pass characteristic with a slope of -18 dB per octave
    • 2L-1H: Bandpass characteristic consisting of 2-pole low pass and 1-pole high pass
    • 1L-2H: Bandpass characteristic, consisting of 2-pole high pass and 1-pole low pass
    • 3HP: High pass characteristic with a slope of -18 dB per octave
    • 1L-2A: Combination of 2-pole all-pass and 1-pole low-pass
    • 1H-2A: Combination of 2-pole all-pass and 1-pole high pass
  • 2-pole output:
    • High pass, bandpass, low pass or all pass characteristics with a slope of -12 dB per octave. (Depending on the 3-pole mode selected)
  • 1-pole input:
    • High-pass or low-pass characteristic with a slope of -6 dB per octave. (Depending on the 3-pole mode selected)

With the mode toggle switch on the module, you can manually change between the bandpass types and all-pass combination. This process can also be controlled via CV. Good to know is that it is also possible to use the filters individually with the 2-pole output and 1-pole input.

Magic Feature: Analog Morphing Without Steps 

The highlight of the Filter Tweek module is the continuous morphing between the different filter modes with the mode knob thanks to the diode circuit. It can also be modulated via CV and goes far into the audio range. Check out my first look to get an idea of this feature. In the center position, the signal is inverted and the filter produces lovely distorted sounds, a bit like an acid filter.


  • cutoff frequency knob + freq CV attenuator
  • 1V/Oct input, made for play filter tonal in self-oscillation (resonance completely clockwise), VCF as VCO.
  • resonance: classic + two variations can be selected with the type switch.
  • LP-comp switch is a bass boost for a constant level even with increasing resonance
  • 2 assignable CV inputs, one with bipolar attenuator and the second with attenuator, switch for turning on/off and inverting.
  • each CV is normalized so can, therefore, function without additional CV at the input.

Funkstill Filter Threek 13700 analog morphing filter is available now for 319€.

More information here: Funkstill

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