Mu-FX Micro-Tron III

The Mu-FX Micro-Tron III is an envelope filter pedal and, in Musitronics Mu-Tron's words, "the newest reincarnation of the classic Mu-Tron III envelope filter"¹. The original Mu-Tron III, made in the 1970s by Musitronics, translated the envelope, or volume picture, of every note into a controlled filter sweep, and the maker described it as producing synthesizer-like sounds from a guitar². The Micro-Tron III carries that circuit into a pedalboard-friendly size, and the maker calls it "a compact, convenient and affordable version of the classic Mu-Tron III envelope filter"¹.

What it does for your sound

An envelope filter opens and closes a filter in response to how hard you play, so the sweep follows your picking rather than a set rhythm. Musitronics Mu-Tron says the Micro-Tron III "provides all the classic Jerry tone and Bootsy funk, in a pedalboard-friendly size", referring to the sounds associated with Jerry Garcia and Bootsy Collins, and says it sounds amazing on guitar, bass, keys, horns, harmonica and more¹. RockBoard's PedalPedia listing repeats the same description³. Pedal of the Day's reviewer noted in 2019 that the pedal is "compact, convenient and a lot more affordable than the original pedals are these days"⁴.

Controls and footswitches

The Micro-Tron III has five controls and two footswitches¹:

The two footswitches are the pedal's most distinctive feature. The maker explains that the UP position produces the familiar "auto-wah" sound, like a heel-to-toe sweep on a wah pedal, while the DOWN position produces a "down swoop" sound, like a toe-to-heel sweep¹. Pedal of the Day's reviewer described the two positions the same way⁴.

Filter modes

The MODE control offers three settings, carried over from the original¹:

• LP (lowpass): passes all the signals below the peak and attenuates signals above the peak¹
• BP (bandpass): passes signals only near the peak¹
• HP (highpass): passes signals above the peak¹

Guitar World's history of the Mu-Tron III confirms the original had the same three settings: "Controls on the Mu-Tron III include a Mode switch with low-pass, band-pass and high-pass filter settings"⁵. On the vintage circuit, the mode selection was a rotary switch; the Guitar FX Layouts technical analysis notes that with only three selections it is easily accomplished with a DPDT on/on/on toggle in modified layouts⁶.

How it differs from the original Mu-Tron III

The Micro-Tron III keeps the classic Mu-Tron III's filter behavior but adds two things the vintage unit did not have: an OUTPUT level control, and the ability to footswitch select between the UP and DOWN drives¹. RockBoard's listing confirms both additions³. The LEVEL control matters in practice because the filter's response changes with input drive, so matching the effected volume to your clean tone is not automatic.

For players tracing the line of Mu-Tron filters, the Micro-Tron III carries the same core controls the original was built around. Its RANGE switch sets the filter sweep to a low range for most rhythm guitar, bass and lower fret uses, or a high range for accenting string harmonics and solo work¹. The PEAK control, also labeled Q, shapes the filter audio response from very weak to very strong¹.

Owner's manual

Musitronics Mu-Tron provides a Micro-Tron III Owner's Manual through the product's page on mu-tron.com¹.

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