MU-FX TRU-TRON 3X

 

02/22/15- This is another trip down nostalgia alley, similar to my article about the Schaller Bow-Wow/Yoy-Yoy pedal that I used in my high school band. In this case, it began as a longing for my '70s Univox Unitron (similar to the pic to the right, which was lifted from the www), which I've read was an very faithful copy of Musitronic's Mu-Tron. I got that pedal shortly after my high school band days, so I don't have a deep nostalgic connection to it from any gigging experience. I remember that it was a fun pedal, albeit somewhat gimmicky. I don't remember why it stopped working, but I assume that I did something bad to it, because I gutted the enclosure and decades later, used that to house my funky "Jimibox" Octavia/Distortion/Univibe Frankenpedal. After the Unitron died, I got an MXR Envelope Filter; I harvested its circuitboard for my experiments in onboard guitar effects and homebrew multi-fx pedal boards (back in the day, before the Rockman and Zoom). It was certainly no replacement for the Unitron, but did a respectable job of its basic "autowah" functionality.

Honestly, I never found the Envelope Filter/autowah to be a terribly versatile effect. I think I used it in exactly one song in my post-college days band, to reinforce the cheesiness of a cheesy C&W tune we did named "Fishnet Hose and Heels" ("Well she was just another hooker, at a truckstop motel..." -JT Steed). But like I said, it was a fun pedal to noodle with. Obviously, your mileage may vary. My favorite example of recorded usage is probably Frank Zappa's solo interlude in "Inca Roads" from "One Size Fits All". (It's a very cool solo, without a speck of cheese.) It was considered a funk effect, and in some ways, brought a hint of the synthesizer sound to the world of electric guitars.

Anyway, my search for a Univox Unitron was fruitless-- it isn't a very well-known pedal, and probably hasn't been produced in nearly half a century. Vintage Musitronic Mu-Trons are readily available on eBay, although relatively pricey. There's a good likelihood that most would need capacitor replacements since those components naturally decline with age (like my brain). There's a more recent incarnation sold in stores that looks almost exactly like the original (Haz Mu-Tron III+), but there's a full-on hate campaign against it because it doesn't use the original circuit design and is not blessed by the original circuit's designer (So I've read...). It was on eBay that I learned that the true successor to the original Mu-Tron was Mu-FX's Tru-Tron 3x, sold by the circuit's original designer and co-founder of Mustronics, Mike Beigel. Unfortunately, it's priced about the same as the cheapest up-priced vintage Mu-Tron, so you'd have to decide whether you're after the sound of the effect (the new one has upgraded functionality and new, reliable components) or the nostalgic vintage vibe (the vintage one has cooler graphics and a larger enclosure).

If you're not familiar with this class of stompbox effect, it's like a wah wah pedal with the treadle sweep controlled by the envelope (attack, amplitude, and decay) of the guitar signal. Like a wah wah, the filter section passes a band of frequencies up and down the frequency spectrum. The old school way of doing this was to have the signal drive a light, which coupled to a photocell to control the wah (filter) circuit in place of the treadle's potentiometer. Similar in some ways to the Univibe circuit, where the light is driven by the variable-rate pulses from an oscillator. I'm not sure how they do it nowadays, but I was surprised to read references to those optocoupler components being hard to find. (Damn, I hate change!) Generally speaking, depending on how you have it set up: Pick hard and the wah circuit goes open, full treble. Pick lightly and it does minor excursions in the bass/closed wah zone. Pick stacatto with palm muting and it does quick popping sounds. Do a volume knob swell and it does a slow wah sweep.

You can see that there are obvious adjustable parameters for this kind of device:

  • Threshold/sensitivity This set the point at which the effect is triggered by strength of the guitar signal. Set the threshold low and a soft signal will make it go "wah", and vice-versa. In the Tru-Tron, this is controlled by the "Mu" and "Preamp" knobs when the "Mu/Pre" switch is set to "Pre". In "Mu" mode, the Mu knob acts alone as the sensitivity and output knob, giving you simplified control (like the original Mu-Tron), but less control over the output level. In "Pre" mode, the knobs are somewhat interactive for setting the desired threshold, but give you more latitude for dialing it in. The Preamp knob also lets you output an overdriven signal.
  • Drive Direction ("Envelope Drive") The direction that the wah filter circuit is driven to produce a "waa" (up) or "oww" (down) sound. Most prefer the up direction.
  • Bandpass Filter Width ("Peak", a.k.a. "Q" or "Resonance") The width of the band of frequencies that are swept up and down. When set widest (counter clockwise), the wah character almost disappears, and when set narrowest (clockwise), the frequencies that are passed are so narrow that they sound thin, "vowel-y" and irritatingly shrill (IMO). As with most control like this, you'll probably prefer a setting that's between these extremes.
  • Filter Range and Mode Switches It's hard to describe what these do in a meaningful manner, except to say that they set the operating zone of the filter. Practically speaking, you'll probably flip the switches and think, "Damn, that sounds like shit!", and permanently settle on positions that sound the best to you.
Some of these filter band setting options seem a little baffling since they seem to provide control over stuff that I don't care much about. Personally, I think I'd prefer/understand it better if there were knobs for setting the lower and upper range limits for the sweep. Also, maybe knobs for setting the attack and decay speed. On the other hand, maybe those would just make it too much of a knob-twiddler's tarpit, with very little practical improvement in functionality. For what it's worth, there are two trimpots inside the enclosure for adjusting the envelope time response and filter range, but the manual strongly discourages messing with the filter range trimpot. By default, it's set up for true bypass operation, but you can move internal jumpers for buffer operation.

Mechanically, it's a very sturdy unit with what appears to be a powder-coated steel enclosure: Very utilitarian. Although large for a pedalboard stompbox, it's significantly smaller than the original version.

Like the original, the input and output jacks are at the top (left to right), as is the jack for the 12-volt A/C wallwart. Notice that this requires 12 volts AC, not DC, so a typical stompbox external power supply won't work, and may do some damage. Unlike the original which ran on 18 volts (two 9-volt batteries), the Tru-Tron can't be powered by batteries. In other words, use the supplied adapter!

Because this is an envelope-controlled effect, placement in the signal chain has a huge effect on how it sounds and operates. My personal preference for wah-wah filters is to place them before distortion effects: I think it produces a more blended and natural tone. Of course, any device that changes gain, placed before the Tru-Tron, will interact with its threshold settings. This can be a useful thing-- effectively, the guitar's volume and tone let you manually control how the Tru-Tron sounds. You can use a DynaComp compressor in front to sculpt the attack and decay, which also compresses the sweep of the wah filter. Putting the compressor after the filter also works, and is my preference. Generally speaking, I think the effect should be fairly close to the front of the chain, nearest the guitar output.

In my opinion, with a nod to thinking objectively, I don't see this as a must-have stompbox for everyone. It's a luxury for guys like me who are fulfilling a nostalgic urge, who like new toys, and who are willing to pay for the privilege. It would probably appeal to fans of the vintage Mu-Tron and those who prefer vintage analog effects. I'm not exactly in that camp since I like cool effects, regardless of the technology. For modern-day guitarists who aren't constrained by that remembrance of a specific vintage vibe, there are probably many reasonably-priced alternatives out there that would make them perfectly happy.

I do like the effect and don't regret the purchase, but... Okay, my memory can be pretty unreliable, but I felt that I couldn't get the same downsweep sound that I got from my old Unitron. From what I remember, it just seemed easier, more intuitive to arrive at the deep "womp womp" sound memory that's burned into my brain. I never played through an original Mu-Tron to know if the Univox Unitron was an exact copy. There's really no way for me to know that now, unless I stumble across an as-new Unitron...


 

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