STmodular: Franz OTA VCF PCB/Panel

STmodular: Franz OTA VCF PCB/Panel


Franz is a 10HP Analog OTA Multimode Filter with an internal LFO and a 3-Channel Mixer.

This is a PCB/Panel in the Eurorack format.

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Availability:In stock

Franz is a 10HP Analog OTA Multimode Filter with an internal LFO and a 3-Channel Mixer.

The filter is based on the CA3080 chip and offers four different outputs:

  • Low Pass
  • High Pass
  • Band Pass
  • Notch

 You may adjust the CUTOFF frequency and RESONANCE by the dedicated knobs. In addition to the filter circuit this module also includes a resettable LFO offering a TRIANGLE and SQUARE wave. The LFO is internally normalled to the Filter CUTOFF and its effect can be attenuated with the knobs CV1/TRI and SQU/CV2. The two waves may be applied at the same time and can be reset with an external trigger source. The normalization of each LFO waveform is interrupted as soon as you plug an external CV source into the CV1 or CV2 input jacks. The LFO Rate may be changed with the LFO Rate potentiometer. Its speed is indicated by a bi-coloured LED.

In order to layer waveforms you will also find a transistor based 3 channel mixer on the bottom of the module. The sum of the mixer is directly routed into the filter and also passed to the MIX output jack. The volume of the mixer inputs can be adjusted per channel (VOL1-3) and all together with the filter INPUT potentiometer.


  • Analog OTA Filter
  • 4 Filter Outputs: Low Pass, High Pass, Band Pass, Notch
  • Internal LFO with two Waveforms: Triangle & Square
  • LFO Reset
  • LED indicating LFO rate
  • LFO normalled to Filter Circuit
  • Apply two LFO waveforms at the same time
  • Attenuator for each LFO Wave or external CV
  • 3-Channel Transistor based Mixer
  • MIX out to use the Filter as a single Mixer Block
  • Volume control for each Mixer Channel
  • Wrong Polarity Protection
  • 3U Eurorack module, 10 HP wide
  • Power consumption: 83 mA at +12 V and 72 mA at -12 V

 The module consists of three boards:

  • Front PCB Panel
  • Control PCB for LEDs, potentiometers and jacks
  • Main PCB
More Information
Brand STModular
HP 10
Additional Resources Build Guide