Mojo Hand FX Wonder Filter

The Mojo Hand FX Wonder Filter is a classically inspired envelope filter pedal: an analog effect that sweeps a filter in response to how hard you pick, the same idea behind the auto-wah sounds of 1970s funk. Mojo Hand FX built it around the voice of the Mu-Tron III, the envelope-controlled filter that started the whole category, and the company describes it as offering "all of the responsiveness and versatility you need to funkify your life," from choppy to smooth¹.

The pedal is discontinued; Mojo Hand FX lists it as such on its product page¹. It was hand-built, fully analog and true bypass, and Premier Guitar's 2021 review put its street price at $229¹².

A Mu-Tron III-style envelope filter

An envelope filter listens to the level of your playing and moves a filter up or down as that level rises and falls. Pick harder and the filter opens; let the note decay and it closes. The effect needs no footwork, unlike a wah, and the sweep follows your touch note for note.

The template for this is the Mu-Tron III, an envelope filter Musitronics released in the 1970s, which Guitar World describes as "an envelope filter called the Mu-Tron III" and which Musitronics still builds today as the Mu-Tron III+ Envelope Controlled Filter, with envelope control of the filter at the heart of the design³⁴. The current Mu-Tron III Vintage Silver reissue carries the same auto-wah, envelope-filter tags⁵.

The Wonder Filter is Mojo Hand FX's take on that circuit. Premier Guitar's reviewer placed it squarely in that lineage, calling out "its classic Mu-Tron-rooted voice"². Where the original Mu-Tron was a large box with a handful of controls, the Wonder Filter packs the concept into a hand-built pedal with a wider control set than most envelope filters offer¹.

The controls and filter modes

The control layout splits between knobs and toggles. Mojo Hand FX kept the Peak and Gain controls from the classic design and added its own features on top¹.

The Mode selector is the pedal's most distinctive feature. Beyond the Band Pass, High Pass and Low Pass settings that shape which part of the spectrum the filter sweeps, it adds a Notch Filter setting and a No Filter setting¹. No Filter takes the filtering out of the chain entirely, and Mojo Hand FX describes it as "offering preamp stand-alone boost capability," which turns the pedal into a clean boost with the Boost knob doing the work¹.

The Mix control matters for players who want the effect subtler than a full-on funk sweep. Premier Guitar's reviewer listed it among the pedal's strengths, citing "fat filter sounds and fluid interactivity. Useful mix control."²

Mojo Hand FX says the pedal works for guitar, bass, keys and more, and the Range toggle's low and high positions are what let you match the filter's operating range to the instrument¹.

Power and bypass

The Wonder Filter runs on a standard center negative 9V DC supply, which is not included, and draws about 60mA¹.

Bypass is true bypass, so with the pedal off your signal passes through unbuffered¹.

The Wonder Filter and the Little Wonder

In September 2020 Mojo Hand FX announced the Little Wonder, a compact sibling to the Wonder Filter. Delicious Audio described it as "a three-knob, stylized, and more intuitive version of it that still offers two filter types (Bandpass and Lowpass)," with controls for Blend, Peak and Gain⁶.

The differences are straightforward. The Little Wonder trims the control set to three knobs and two filter types, where the Wonder Filter carries the full complement: five mode settings, Attack, Boost, Mix, and the Range and Drive toggles¹⁶. A player who wants the Mu-Tron-style sound with minimal tweaking has the smaller box; a player who wants to fine-tune the response, blend the effect, or use the No Filter boost needs the Wonder Filter's extra controls.

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