VCV Rack Modules

These modules are not regular plugins, but modules to load inside VCV Rack. Once VCV Rack is installed you can run it standalone, or load it as a plugin inside any DAW.

They can be purchased on the VCV Rack Library page.

CF100

The CF100 is a highly detailed analog model of the classic cascade filter found in the early Prophet synthesisers which used the SSM2040 filter chips. This model is based off the Discrete OTA schematic created by Jürgen Haible, with some extras added including multiple filters responses, and extra input and output saturation options. It runs without internal oversampling over the full range of frequencies. Oversampling can be optionally done using VCV Racks sample rate settings, and is recommended for patches where large amounts of drive or stronger sounding high frequency resonance is required.

Input Controls:

  • DRIVE (0 to 10) – Exponential input gain amount from -inf dB up to +12 dB. Voltage controlled from the DRIVE CV input port.
  • FREQ (8hz to 30khz) – Exponential cutoff frequency of the filter. Can be controlled by the 1V/Oct, FM1, and FM2 CV input ports.
  • RES (0 to 10) – Linear resonance control, self oscillates at around 7.5. Voltage controlled from the RES CV input ports.
  • DRV Mod Depth (0 to 10 CV depth)
  • FM1 Mod Depth (0 to 10 CV depth)
  • FM2 Mod Depth (-5 to 5 CV depth)
  • RES Mod Depth (0 to 10 CV depth)

Input Ports:

  • DRIVE (CV in)
  • FM1 (CV in)
  • 1V/OCT (CV in)
  • FM2 (CV in)
  • RES (CV in)
  • IN (audio in)

Output Ports:

  • NPN2 (audio out) – twin 2 pole notch filter, with one notch an octave above the cutoff, and another an octave below. This response has lots of phase shift and sounds a bit like a phaser.
  • HP2 (audio out) – 2 pole high pass
  • BP4 (audio out) – 4 pole band pass, with a 2 pole high pass and two pole low pass both centred at the cutoff.
  • LP2 (audio out) – 2 pole low pass, with lots of character and drive
  • LP4 (audio out) – 4 pole low pass, with tamed and deeper character and drive

Right click options:

  • Boost Input – Off, +6dB, and +12 dB. This changes the input level just like moving the DRIVE knob but allows for extra gain
  • Boost Output – Off, +6 dB, and +12 dB. This places gain between the output of each of the filters stages and an Op-Amp that clips to the voltage rails. Increase this for post filter distortion.
  • Circuit – AC JH, DC JH, DC Datasheet. The AC version is for audio, the DC versions can be used for either CV or Audio. The JH is the original CF100, and the Datasheet version is based on the schematic shown in the SSI2140 datasheet.
  • Noise Level – Off, Input Only, 50%, 100%, 150%, 200%. Analog modelled thermal hiss. 100% is true to the analog circuit.
  • PNP BF – 40, 400, 4k. Forward beta value of the PNP transistors used in the circuit. 40 gives more 2nd order harmonics, 400 is the default, and 4k reduces 2nd order harmonics.
  • Oversampling – Off, x2, x4. The oversampling multiplier to increase the sample rate used by the module internally, which reduces aliasing and gives stronger resonance
  • Knob LED Brightness – Off, 25%, 50%, 75%, 100%

Credits:

Audio Examples

  • Filter Types Intro

    A sawtooth waveform being filter with various amounts of drive and resonance to show how the filter behaves.

    0:00 – LP4 with different drive and resonance.

    0:44 – LP2 with different drive and resonance.

    1:20 – BP4 with different drive and resonance.

    2:13 – HP2 with different drive and resonance.

    3:11 – NPN2 with different drive and resonance.

    4:45 – LP4 fade out.

  • Stereo Bass and Arp

    A basic song with a stereo bass and arp, with various filter sweeps and changes in drive and resonance.

    0:00 – Bass using LP4.

    0:28 – Arp using LP2.

    1:06 – More melodic variation.

    1:58 – Just Bass and Arp.

  • Deep Bass Growl

    A basic bassline with increasing amounts of drive being added.

    0:00 – Low Drive.

    0:29 – Medium Drive.

    0:43 – High Drive.

    1:00 – High Drive with Resonance.

  • Pad Sin Wobble

    A deep pad sounds is created with self oscillating resonance tuned to the same pitch as the oscillator. As the song progresses the cutoff of the filter is slightly changed to beat against the oscillator.

    0:00 – Tuned resonance at the same pitch as the oscillator.

    0:29 – Slightly detuned cutoff so it beats against the oscillator.

    1:02 – More detuning of the cutoff.

Change Log

v2.0.0 (2023 Jul 7) – Initial release of the CF100

v2.0.1 (2023 Jul 11) – Increased resonance slightly, and added support for PNP BF (forward beta) customisation

v2.0.2 (2023 Jul 13) – Calibrated the self oscillation tuning at 1000hz on the freq knob to 1000.00hz using a resonance of 7.5, PNP BF 400, sample rate of 44.1khz

v2.0.3 (2023 Jul 14) – Added oversampling support via a right click menu: Off, x2, x4

v2.0.4 (2023 Jul 30) – Added a DC blocking toggle. Added detailed noise modelling. Added LEDs to knob dots. Fixed right click Initialize.

v2.0.5 (2023 Jul 30) – Swapped the DC blocking toggle to a Circuit choice: AC JH, DC JH, DC Datasheet

v2.0.6 (2023 Aug 19) – Working macOS arm64 build