F-1:  Stereo Lowpass Filter


Bob Moog's "transistor ladder" filter is a work of genius. This brilliant design uses a small number of components to achieve the warm and fat sound that has inspired generations of musicians. When designing our F-1: Stereo Lowpass Filter, we researched many filter topologies but ultimately came back to the elegant transistor ladder as our starting point. From there, we added modern touches like linked-stereo (or dual-mono) operation, 12/18/24dB slope/octave selection, and temperature compensation for accurate tracking. 

No compromise Stereo Lowpass Filter.

At the core of our F-1 module, you will find a no compromise design with two tightly matched transistor ladder filters. Why two filters? Because we love stereo sound and all the sound-stage and phase information it carries. We think it's a shame to down-mix all of your sounds to mono before sending them through a typical filter. F-1 lets you avoid this and opens exciting stereo synthesis possibilities, especially when paired with our M-4 Advanced Stereo Mixer. If you just need two separate (mono) filters, no problem–the F-1 has you covered there too!

Beyond modular synthesis, you can also use F-1 to breathe analog life into your old drum machines, digital synths, virtual instruments or even apps on your phone or tablet. The possibilities are far reaching.

Knobs and CV controls:

  • Sat (Saturation) - This knob controls each channel's input gain level. Unity gain is around the "12:00" position. Turning beyond this point lets you overdrive the channel to achieve varying degrees of glorious analog distortion. You can then filter that overdriven sound if you wish.

  • Cut (Cutoff) - This knob sets the cutoff frequency. Cutoff frequency can also be controlled via CV input. The slope or "steepness" of the filter is set by the Filter Order switch.

  • Res (Resonance) - This knob sets the resonance amount of each channel, ranging from no resonance to maximum. Resonance can also be controlled via CV input.

  • Out (Output) - Sets the output level for each channel. This provides sonic options. For example, drive the input harder to achieve analog distortion while reducing output levels to avoid excessive output. Conversely, create a super-clean sound by driving the input lightly and making up the low output level by turning up the output knob.

When Stereo Link activated, the left channel knobs and CV-inputs control both channels (the right-channel controls and CV inputs are ignored). This lets you use one knob or CV source to easily control both channels when working with stereo signals. When Stereo Link is switched off, the left and right channels work independently, effectively giving you two separate filters in one module.

To maximize sonic versatility, the Filter Order switch lets you choose between second, third, or fourth order filters (12, 18 or 24 dB/octave, respectively). Each of these modes affects the sonic characteristic of the module, so it's like getting three filters in one:

  • 2nd order - Provides a "well-behaved" 12dB/octave slope with no self oscillation.

  • 3rd order - Slightly more "assertive" sound with 18dB/oct. slope (TB-303 style). No self oscillation.

  • 4th order - Aggressive (Minimoog style) sound with sharp 24dB/oct. slope and self-oscillation.

Finally, we include a Cutoff Offset knob that lets you introduce a deliberate offset between your two filter cutoff frequencies. When the knob is in the detented "12:00" position, the two cutoff frequencies are precisely matched but as the knob is turned clockwise or counter-clockwise, the two cutoff frequencies are "pushed" away from each other around a central frequency. This knob works regardless of how the Stereo Link switch is set, so you can use it to create some very interesting stereo effects when working in stereo or formant filter style effects when working in dual-mono.

Key Features:

  • Tightly Matched Stereo Filter

  • Transistor Ladder design provides classic Moog sound

  • Stereo Link mode when filtering stereo sources or use dual-mono

  • Filter Order switch lets you select between 2, 3 or 4 pole filters (i.e., 12, 18, 24dB/Octave)

  • Cutoff Offset knob for wild stereo or formant style effects

  • CV control of both filter Cutoff and Resonance for each channel

  • 16HP wide, 41 mm depth (rail-to-back)

  • CNC machined, infilled aluminum front panel (no silk-screen)

  • Made in the USA




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