The PastFX PX-101 is a lowpass filter pedal, an envelope filter and auto wah in a compact stompbox. It is PastFX's take on the discontinued Moogerfooger MF-101 Lowpass Filter, shrinking the original's large format into a pedalboard-friendly box and adding a Level control the MF-101 did not have1. Guitar Pedal X's Stefan Karlsson described it plainly:
"PastFX's PX-101 is a replica of the Moogerfooger MF-101 Lowpass Filter, adding an Output Level control while retaining its control topology."2
Guitar Pedal X, July 20242
A lowpass filter with an envelope follower works differently from a wah you rock with your foot. The pedal tracks the level of your playing, and the harder you pick, the more the filter cutoff sweeps, opening up brightness on loud notes and closing down on quiet ones. The result is the quack and bounce associated with funk bass and disco guitar, without touching a treadle.
What it does to your sound
The PX-101 filters out high frequencies above a cutoff point, and that cutoff moves in response to your playing dynamics through the envelope follower. The Envelope Amount control sets how much the envelope signal modulates the filter cutoff1. The 2/4 Pole switch chooses how much of the filter circuit the signal passes through: 2 Pole for a brighter sound, 4 Pole for a deeper, mellower one1.
The Mix control blends between filtered and unfiltered signal, and it has a second trick. PastFX notes that turning Mix fully counter-clockwise gives you the "Preamp" sound without the filter, so the pedal can act as a straight preamp when you want it to1.
Guitar Pedal X found the pedal covers a lot of ground tonally: "It suits guitar, bass, synth, drum machines and beats, covering funk, boogie, disco and sci-fi tones"2. The underlying MF-101 design is a mono input and output device, so it handles one signal chain rather than stereo sources3.
Controls
| Control | What it does |
|---|---|
| Drive | Adjusts the signal input gain1 |
| Envelope Amount | Controls how much the envelope signal modulates the filter cutoff1 |
| Mix | Blends filtered and dry signal; fully counter-clockwise gives the "Preamp" sound without the filter1 |
| Level (Master Level) | Sets output level; new versus the original MF-10112 |
| Smooth/Fast | Switches the envelope follower between smooth and fast attack modes2 |
| 2/4 Pole switch | Half or all of the filter: 2 Pole brighter, 4 Pole deeper and mellow1 |
The Smooth/Fast switch follows the original MF-101's approach, where the envelope follower can be switched between fast and smooth attack modes for producing sweeps3.
Expression pedal control
The EXP jack takes an EP-3 expression pedal or similar with a 50K to 100K linear pot, and from it four parameters can be controlled: Mix, Amount, Resonance and Cutoff1. Guitar Pedal X also notes that the Audiostrom MXP-1 expression pedal is supported2. With cutoff on an expression pedal, the pedal can be swept manually like a wah rather than driven by the envelope.
Where it came from: the Moogerfooger MF-101
The PX-101 traces back to the Moog MF-101 Lowpass Filter, part of Moog's Moogerfooger line of voltage-controlled analog effects inspired by original Moog synth modules41. Vintage Synth Explorer describes the MF-101 as a stomp-box style Minimoog VCF, the same filter design found in the Minimoog synthesizer, with knobs for filter cutoff, resonance, envelope amount and more3. Gearnews' Robin Vincent notes the MF-101 and its sibling MF-102 Ring Modulator were based on original synth-module designs5.
The Moogerfooger line has since been discontinued, which is what creates the opening the PX-101 fills. The original MF-101 measured 130mm by 230mm and had larger format rocker switches and wooden side panels; the PX-101 comes in at 60mm by 112mm, with the rocker switches replaced by space-saving toggle switches2.
The original Moogerfooger MF-101 is discontinued. The PX-101 is PastFX's compact take on that circuit, not a Moog product.
What reviewers said
Guitar Pedal X's Stefan Karlsson reviewed the PX-101 at its July 2024 pre-order launch:
"The PX-101 certainly injects a lot of bounce into your signal. And I had a lot of fun working my way through the various"2
Guitar Pedal X, July 20242
In the site's year-end roundup of the best new modulation and utility pedals of 2024, the PX-101 was named "an absolute essential for Bass / Funk Players"6. The original MF-101 drew its own praise over the years, summed up in one collected review as "a simple but great sounding filter with envelope following abilities"7.
Videos
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Questions
Is the PastFX PX-101 a copy of the Moogerfooger MF-101?
Yes. Guitar Pedal X describes it as a replica of the Moogerfooger MF-101 Lowpass Filter, and PastFX calls it their take on the discontinued original. It keeps the filter and envelope follower circuit concept but moves it into a much smaller enclosure, replaces the original's rocker switches with toggle switches, and adds an Output Level control the MF-101 did not have.
Does the PastFX PX-101 have an output level control?
Yes. The PX-101 includes a Master Level control, which is new relative to the original Moogerfooger MF-101. PastFX lists the Level control among the pedal's features, and Guitar Pedal X notes the added Output Level control as one of the changes made to the original design.
Can the PastFX PX-101 use an expression pedal?
Yes. It has an EXP jack that works with an EP-3 expression pedal or similar, using a 50K to 100K linear pot. Four parameters can be controlled from it: Mix, Amount, Resonance and Cutoff. Guitar Pedal X also notes support for the Audiostrom MXP-1 expression pedal.
What instruments does the PastFX PX-101 work with?
Guitar Pedal X found it suits guitar, bass, synth, drum machines and beats, covering funk, boogie, disco and sci-fi tones. The underlying MF-101 design is a mono input and output device, so it processes one signal at a time rather than stereo sources.
How big is the PastFX PX-101?
PastFX lists the enclosure at 112 x 60 x 31mm, or 4.4 by 2.36 by 1.22 inches, enclosure only. Guitar Pedal X measures it at 60mm by 112mm, against the discontinued original Moogerfooger's 130mm by 230mm, making it a much smaller footprint on a pedalboard.
Sources (7)
- PX-101 LOWPASS FILTER, pastfx.com, 2026
- Guitar Pedal X, Guitar Pedal X, 2024-07-26
- Moog MF-101 Lowpass Filter, Vintage Synth Explorer, 2026
- Moog sunsets Moogerfooger effects, Guitar.com, 2018-08-28
- Moog Music announces that Moogerfooger has reached the end of the line, gearnews.com, 2018-08-27
- Guitar Pedal X, Guitar Pedal X, 2024-12-19
- Reviews, Sherman (www.sherman.be)
