The Mu-FX Tru-Tron 3X is an all-analog envelope controlled filter pedal, described by its maker as "the modern all-analog refinement of the classic Mu-Tron III™ envelope controlled filter"1. An envelope filter, also called an auto-wah, listens to how hard you pick and sweeps a filter in response, so the effect follows your playing dynamics instead of a foot rocking back and forth. At its heart, the maker says, the circuit is the Mu-Tron III, the 1972 pedal that was the very first commercial envelope filter12.
What makes the Tru-Tron 3X distinct is who built it. It was designed and produced by Mike Beigel, the inventor and designer of the original Mu-Tron III and co-founder of Musitronics Corp.1. In 2013 the Tru-Tron 3X became, in the maker's words, "the true official successor to the Mu-Tron legacy"3.
An envelope filter descended from the Mu-Tron III
The Musitronics Mu-Tron III was released in 1972 and was the first commercial envelope filter effect2. Premier Guitar's builder profile on the Mu-Tron story calls it "the first envelope-controlled filter in modular form"7. The original had six simple controls, three knobs and three switches, which let a player tweak the filter in a number of ways8.
The Tru-Tron 3X keeps that DNA. Premier Guitar's review notes that "the optical filter control circuitry and control set of the Mu-Tron III is at the foundation of the Tru-Tron 3X"4. Where the original had a fixed relationship between the signal driving the envelope and the signal driving the filter, the 3X splits those into two independent controls, and it adds a MIX mode and a stronger peak. MusicRadar's NAMM 2014 announcement described it as "the authorized modern all-analog re-issue and refinement of the classic Mu-Tron III™"9.
A small number of units printed with "Mu" instead of "Tru" were unearthed and released as collector's items; inside, they are identical to the Tru-Tron units6.
The controls
The control set splits into knobs and switches, with the MU/PRE switch deciding how the two main knobs behave169.
| Control | What it does |
|---|---|
| PRE knob | Controls the preamp drive1 |
| MU knob | Controls the envelope and filter audio drive1 |
| MU/PRE switch | Determines the PREamp and ENVelope drive modes of the device1 |
| Mode knob | Selects low-pass, high-pass, band-pass, and MIX modes4 |
| PEAK control | Sets resonance; the 3X peak is much stronger, from about 9 to 11 on the dial1 |
| Filter Range toggle | Adjusts the range of the filter sweep, lower end for rhythm work or higher end for lead tones6 |
| Envelope Drive toggle | Up selects auto-wah mode, Down selects a "down swoop" mode6 |
The MU/PRE switch is the heart of what is new. In the MU position, the pedal "works exactly like the original Mu-Tron III"1. In the PRE position, the MU knob controls only the envelope drive and the PRE knob controls only the filter audio drive1. MusicRadar summed this up as "MU and PRE controls for independent control of envelope drive and audio gain"9.
The mode knob selects between low-, high-, and band-pass filters, plus a new mix mode4. In LP mode, the low-pass filter passes all the signals below the peak and attenuates signals above the peak1. MIX mode is an optimized mixture of the dry, unfiltered signal and the filtered signal, which the maker included for quick and easy setups6.
The Envelope Drive switch sets the sweep direction. Its 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" sound1.
Power and connections
The Tru-Tron 3X runs on 12VAC, not DC. A 12VAC 200mA adapter is included in the box1. Standard 9V DC pedalboard supplies and daisy chains will not power it, so it needs its own adapter or an isolated supply with an AC output.
The box contains the pedal, the 12VAC power supply, the owner's manual, and a Mu-FX sticker1. Connections are simple: 1/4" input and output jacks1.
Specifications from the maker1:
| Specification | Value |
|---|---|
| Input impedance | 390K Ohms |
| Nominal input level | -10dBu |
| Output impedance | 150 Ohms |
| Nominal output level | -10dBu |
| Maximum output level | +16dBu |
| Signal to noise ratio | 85dB or better |
| Dimensions | 7" x 4 15/16" x 2 1/4" |
| Weight | 16.3oz/462g (unit only) |
Bypass is true bypass, convertible to active, so the pedal can sit fully out of the signal path when off or run as an active preamp bypass if the rig calls for it1.
History: Mike Beigel and the Mu-Tron successor
Mike Beigel co-founded Musitronics Corp. and designed the Mu-Tron III, released in 197212. He founded Mu-FX in 2013 to produce more compact renditions of his '70s classics, and the Tru-Tron 3X, designed and produced by Beigel, became the official successor to the Mu-Tron legacy that year3. Guitar World notes that "a modified version was also released in 2014 by Beigel's new company Mu-FX"8.
The pedal was announced and began shipping in January 2014, available in the USA direct only from Mu-FX for $379.735. MusicRadar covered the announcement at NAMM 2014, noting that Beigel "has retained all the sonic" character of the original9. Vintage Guitar reviewed it in May 2014 at a price of $369.6310. By April 2016 it had sold out once again, with demand matching the older models6. Premier Guitar's 2021 review listed it at a $295 street price4.
What reviewers said
Premier Guitar's review credited the pedal with "Authentic Mu-Tron III tones. Independent filter gain for overdriven sounds. Excellent build quality."4 The same review highlighted the mode knob's new mix mode as "a useful new mix mode" alongside the low-, high-, and band-pass filters4.
The maker's own claim is a strong one: "The Tru-Tron 3X is bar none the best envelope filter pedal for guitar. Actually, the Tru-Tron 3X is the best envelope filter for bass, keyboards, sax or any instrument that can be plugged in"1. That is Mu-FX's marketing voice, not a reviewer's, but it points at something the history backs up: the original Mu-Tron III was a classic effect used by numerous musicians across instruments6, and the 3X carries the same instrument-agnostic design, with a nominal input level of -10dBu and a maximum output of +16dBu that leave headroom for hotter signals than a guitar alone1.
Videos
Premier Guitar
Mu-FX
Mu-FX
Questions
Does the Tru-Tron 3X sound like an original Mu-Tron III?
In MU mode it works exactly like the original Mu-Tron III, and Premier Guitar's reviewer found it delivers authentic Mu-Tron III tones. It also goes further: the peak control is much stronger, reaching about 9 to 11 on the dial, and it can achieve higher Q than the original when needed.
Can the Tru-Tron 3X run on a 9V power supply?
No. The Tru-Tron 3X runs on a 12VAC 200mA adapter, which is included in the box. That AC power requirement rules out standard 9V DC pedalboard supplies and daisy chains, so plan a dedicated outlet or an isolated supply with an AC output.
Is the Mu-FX Tru-Tron 3X true bypass?
Yes. The maker lists it as true bypass, convertible to active preamp bypass. That means you can run it fully out of the signal path when off, or switch to an active buffered bypass if your rig needs it.
Does the Tru-Tron 3X work on bass?
Yes. The maker describes it as the best envelope filter for guitar and also for bass, keyboards, sax, or any instrument that can be plugged in. The original Mu-Tron III was itself used by numerous musicians across instruments.
Who designed the Mu-Tron III?
Mike Beigel, co-founder of Musitronics Corp., invented and designed the Mu-Tron III, the first commercial envelope filter, released in 1972. He later founded Mu-FX in 2013 and designed the Tru-Tron 3X as the official successor to the Mu-Tron legacy.
Is the Tru-Tron 3X the same as a Mu-Tron III?
It is an authorized all-analog reissue and refinement of the Mu-Tron III, built around the same optical filter control circuitry and control set. In MU mode it works exactly like the original, but it adds a PRE mode, a stronger peak control, a MIX mode, and true bypass.
Sources (10)
- Mu-FX Tru-Tron 3X, Musitronics Mu-Tron
- Lumitron Resonant Filter / Mu-tron® III, Aion FX, 2023-09-08
- Mike Beigel, Musitronics Mu-Tron (mu-tron.com)
- Beigel Sound Lab/Mu-FX Tru-Tron 3X Review, Premier Guitar, 2014-08-03
- Beigel Sound Labs Unveils the Tru-Tron 3X, Premier Guitar, 2014-01-22
- Mu-FX Tru-Tron 3X™ Envelope Filter, Pedal of the Day, 2016-04-19
- Builder Profile: The Mu-tron Story, www.premierguitar.com, 2013-09-12
- The Mu-Tron III: “Without it, there ain't no Bootsy”, Guitar World, 2023-03-17
- NAMM 2014: Beigel Sound Lab announces Tru-Tron 3X pedal, MusicRadar, 2014-01-27
- Mu-FX Tru-Tron 3X, Vintage Guitar magazine, 2015-09-04
