Strange Science Instruments - F1 Stereo Lowpass Filter


Far more than just a Moog clone! – The F1 consists of two voltage-controllable transistor ladder low-pass circuits. The filters can be used individually or as a linked pair with optional offset. Thus, besides separate respectively parallel operation, it is also possible to evenly process stereo material or to create serial patches with two shifted resonance peaks. Thanks to three switchable filter slopes, you can not only enjoy classic Moog sound, but also alter signals in a velvety soft fashion. Saturation stages add roaring overdrive, if desired.



The F1 is a two-channel transistor ladder filter with a unique feature set. The audio inputs are followed by a combination of level control and saturation stage. With the associated potentiometers in 12 o’clock position, you have unity gain. Higher settings make the saturation stages produce beefy distortion.

Next in line are the actual filters. Cutoff frequencies and resonance values are not only editable by hand, but can also be controlled via CV inputs. The edge steepness is chosen for both filters. The following options are available:

  • -12 dB per octave: In this mode of operation, the F1 features a very gentle sound character. It is somewhat reminiscent of the Oberheim SEM filter. The resonance can be used to sharpen signals. Self-oscillation is not possible in this mode of operation. We recommend the -12 dB per octave setting for creating soft leads and pads. Furthermore, this mode is perfect while playing live, as sounds can be faded in and out very smoothly.
  • -18 dB per octave: Every bit as charming as the -12 dB mode, yet cutoff and resonance are noticeably more powerful. Combined with the roaring saturation, you can create twitchy basses with a little TB-303 flavor.
  • -24 dB per octave: Classic Moog sound! The resonance is meticulously fine-tuned. Self-oscillation is reached only right before the end of the potentiometers' control ranges. The sensitive calibration gives the F1 an almost surgical character.

As usual with transistor ladder circuits, low frequencies are properly thinned out by high resonance values. You can take countermeasures via the saturation stages. An offset control makes it possible to set the cutoff frequencies of both channels apart from each other. A tip: With both filters receiving the same audio signal, vocal-like sounds can be produced at high resonance values and offset cutoff frequencies. Connecting the VCFs in series, on the other hand, gives you to resonance peaks. – Also very interesting for sound experiments. Without an offset, an edge steepness of -48 dB per octave may be created by wiring both filters in series.

Level increases generated by the saturation stages can be compensated with the help of additional volume controls right in front of the audio outputs.

An important feature of the F1 module is the Stereo Link switch. While active, all parameters of both channels can be controlled solely by the potentiometers and CV inputs on the left side of the front-panel. – Perfect for modular DJ sessions and live performances.


Per filter:
Audio input and output
Cutoff CV input
Resonance CV input


3U Eurorack module, 16 HP wide, 35 mm in depth
Power consumption: 70 mA at +12 V and 65 mA at -12 V

0.2 kg
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