The Mu-Tron Micro-Tron III is an analog envelope filter pedal, the modern, compact reincarnation of the classic Mu-Tron III auto-wah first built by Musitronics Corp. in 1972. It tracks your playing dynamics and sweeps a filter in response, producing the "auto-wah" effect, and its maker says it delivers "all the classic Jerry tone and Bootsy funk, in a pedalboard-friendly size"1. It runs on standard 9V DC power1.
What it does and where it came from
An envelope filter, often called an auto-wah, opens and closes a filter automatically according to how hard you play, rather than being rocked by foot like a wah pedal. The original Mu-Tron III became the reference point for the effect type, and Guitar World notes its controls included "a Mode switch with low-pass, band-pass and high-pass filter settings"3. The original is long out of production4, and vintage units have since become expensive and collectible.
The Micro-Tron III is the newest version of that circuit from the revived Mu-Tron brand, described by RockBoard's PedalPedia as "the newest reincarnation of the classic Mu-Tron III envelope filter"1. Pedal of the Day reviewed it in July 2019 as "compact, convenient and a lot more affordable than the original pedals are these days"2.
Controls and modes
The Micro-Tron III keeps the control layout of the original Mu-Tron III and adds to it. Pedal of the Day notes that the original pedal featured Mode, Peak and Gain knobs as well as Range and Drive switches, "these are all present in the Micro-Tron III"2.
| Control | What it does |
|---|---|
| GAIN | Controls the envelope and filter audio drive5 |
| LEVEL | Controls the output volume of the effected signal5 |
| Mode knob | Selects Lowpass, Bandpass or Highpass filters2 |
| Range switch | LO sets the sweep to a low range for rhythm guitar, bass and lower frets; HI sets a high range for string harmonics and up-the-neck solo work2 |
| Up/Down footswitch | UP gives the familiar auto-wah sweep, like heel-to-toe on a wah pedal; DOWN gives a down-swoop, like toe-to-heel2 |
The Mode knob carries over the original's three filter choices. On the vintage pedal this was a rotary switch; as the Guitar FX Layouts technical analysis put it, "the original included a rotary switch for the Mode selection, but there are only 3 selections"6, which is why the modern layout can use a simple toggle or knob instead. The added LEVEL control is a practical change: the original had no output volume of its own, so matching your clean tone meant working around the amp or other pedals.
Using it on bass and beyond
The maker positions the Micro-Tron III as a multi-instrument filter, saying it "sounds amazing on guitar, bass, keys, horns, harmonica and more"5. For bass players, the LO range mode is the relevant feature: Pedal of the Day describes it as setting the sweep "to a low range for most rhythm guitar, bass and lower fret uses"2, keeping the filter sweep where a bass signal lives, while HI suits harmonics and lead work.
What reviewers said
Pedal of the Day's 2019 review came down in favor of the compact format. The reviewer wrote2:
Pedal of the Day's reviewer came away sold on the compact design, finding that the Micro-Tron III sounds fantastic and preferring it overall to the Tru-Tron 3X Envelope Filter2.
The reviewer was sold on the compact design, found it sounds fantastic, and preferred it overall to the larger Tru-Tron 3X, another modern Mu-Tron-style filter2.
Videos
Pedal of the Day
Tri Pedal Reviews
Sugaree Licks
Questions
What power does the Mu-Tron Micro-Tron III need?
The Micro-Tron III runs on industry-standard 9V DC power, the same supply most pedalboards already use. A standard center-negative pedal supply will cover it, so no special adapter is needed alongside your other pedals.
Is the Micro-Tron III analog?
Yes. The Micro-Tron III is an analog circuit, listed with analog as its circuit type. It is a modern, compact reincarnation of the original 1972 Mu-Tron III envelope filter rather than a digital model of it.
What is the difference between the Micro-Tron III and the original Mu-Tron III?
The Micro-Tron III is described by its maker as the newest reincarnation of the classic Mu-Tron III envelope filter, in a pedalboard-friendly size. The original pedal, made by Musitronics Corp. and first released in 1972, was out of production by 1979 or 1980. The Micro-Tron III adds an output level control and keeps the original's Mode, Peak and Gain knobs and Range and Drive switches.
Can the Micro-Tron III be used on bass?
Yes. Musitronics Mu-Tron says the Micro-Tron III sounds amazing on guitar, bass, keys, horns, harmonica and more, and the reviewer at Pedal of the Day noted that the LO range mode suits bass and lower-fret rhythm playing.
Who makes the Mu-Tron Micro-Tron III?
The Micro-Tron III is made by Mu-Tron, also badged as Mu-FX, the revived brand of the company that built the original Mu-Tron III. That original pedal was made by Musitronics Corp. and first came out in 1972.
Sources (6)
- Micro-tron III by Mu-Tron, RockBoard PedalPedia, 2026
- Mu-Tron Micro-Tron III Envelope Filter, Pedal of the Day (pedal-of-the-day.com), 2019-07-10
- How the Mu-Tron III became a vintage pedalboard icon, Guitar World, 2026-02-09
- Mu-FX Tru-Tron 3X, Vintage Guitar magazine, 2015-09-04
- Mu-FX Micro-Tron III, Musitronics Mu-Tron
- Guitar FX Layouts: Mutron III, Guitar FX Layouts (tagboardeffects.blogspot.com), 2014-06-19
Tim Mahoney
