The Mu-Tron Tremu-Tron A Stock from Musitronics is an optical tremolo pedal that can also be used as a clean boost. Musitronics designed it to give non-tremolo tube and solid state instrument amplifiers the same rich tremolo found in vintage Fender and Vox amplifiers, and it carries the famous Mu-Drive preamp from the original Mu-Tron III envelope filter1. Pedal of the Day reviewed the Tremu-Tron in 2022 and found that it "delivers on all modulation fronts, awakening both your amplifier and your musical muse"2.
The "A Stock" part of the name is the interesting bit. These are the same pedals as the regular Mu-Tron Tremu-Tron, but with very minor cosmetic blemishes on the case. Musitronics says there are no issues internally and that A Stock units hold the same warranty as the non-A Stock version, so the difference is a few dollars in exchange for a mark on the enclosure1.
An optical tremolo that doubles as a clean boost
Tremolo works by repeatedly raising and lowering the volume of your signal in a repeating cycle, the effect built into many vintage amplifiers. The Tremu-Tron does this optically rather than with a purely electronic voltage control. Musitronics says the pedal "utilizes Mu-Tron's patented opto-mod technology to provide classic, hi-fidelity attentuation without extra noise artifacts"1.
Opto-mod is the same family of technology behind the original Mu-Tron envelope filters. Those circuits, which Premier Guitar notes were "created with an original Musitronics Mu-Tron III," used photo-couplers, components also known as optocouplers, photocouplers or vactrols, to control the signal path with light34. In the Tremu-Tron the same idea is applied to volume modulation: a light source and a light-dependent element shape the signal, which is how the maker gets the smooth, vintage-style attenuation.
The boost side comes from the preamp. The Tremu-Tron features the Mu-Drive preamp from the original Mu-Tron III envelope filter, the input stage that gave those pedals their character1. With the tremolo turned down through the Blend control and the Level control raised, the pedal works as a level boost for your signal.
Musitronics also suggests where the pedal belongs on your board: "The TREMU-TRON pedal should be placed after overdrive and before reverb in the signal chain"1. That is the conventional spot for a tremolo, after your overdrive and distortion pedals and before time-based effects like reverb and delay.
The controls
The Tremu-Tron has four knobs, and each one is straightforward:
| Control | What it does |
|---|---|
| Rate | Controls LFO speed, the speed of the tremolo pulse1 |
| Level | Controls overall output level of the signal1 |
| Shape | Controls the waveform from sine to square1 |
| Blend | Controls the amount of tremolo applied to the dry signal1 |
Rate and Shape together define the character of the pulse. A slow Rate with a sine wave gives the smooth, amp-like swell associated with vintage Fender tremolo; a faster Rate pushed toward square gives a choppier, more percussive chop. Blend is the control that makes the pedal flexible: turning it down mixes more of your dry signal in, which is also how you set the pedal toward clean boost territory, with Level setting how hard the output hits the front of your amp.
Power: 9V DC with an 18V internal rail
The Tremu-Tron runs from a 9V DC supply in its rugged Mu-Tron enclosure, but internally it operates on a higher voltage. Musitronics explains the benefit: "By utilizing an 18 volt dual-rail internal power supply, the TREMU_TRON provides a crisp, clean signal and high headroom"1.
For a player, headroom is the practical point. A tremolo that modulates volume can run out of room when the Level control is pushed, and a boost pedal needs clean overhead above your input signal to raise the level without clipping. The pedal uses an 18 volt dual-rail internal power supply, which provides a crisp, clean signal and high headroom, and it is 9V DC powered in a rugged Mu-Tron enclosure1.
What "A Stock" means
A Stock is Musitronics' own designation for cosmetically blemished units sold at a discount. The maker's description is direct: "Save a few dollars with very minor cosmetic case blemishes. No issues internally and hold the same warranty as non a stock"1. At the time of writing, the A Stock price is $174.00 against a regular price of $189.001.
Everything else is the same pedal: same circuit, same opto-mod technology, same Mu-Drive preamp, same controls, same 9V DC power with the 18V internal rail, and the same 1 year limited warranty1. The only trade-off is the finish of the enclosure, which for a pedal that lives on a board is a trade some players will take happily.
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Questions
What does "A Stock" mean on a Tremu-Tron?
A Stock units are Tremu-Trons with very minor cosmetic blemishes on the case. Musitronics says there are no issues internally and that they carry the same one year limited warranty as the non-A Stock version. The discount is the only practical difference: the A Stock price is $174.00 against the regular $189.00.
Can the Tremu-Tron be used as a clean boost?
Yes. Musitronics describes the Tremu-Tron as an optical tremolo effect which can be used as a clean boost. The Level knob controls the overall output level of the signal, and the Blend knob lets you dial back the amount of tremolo applied to the dry signal, so the effect can be set toward a straight level boost.
What does the Shape knob do on the Tremu-Tron?
Shape controls the waveform of the tremolo's low frequency oscillator, moving continuously from a sine wave, which gives a smooth, rounded pulse, to a square wave, which gives a harder on-off chop. Between the two you can find the in-between shapes that suit the part you are playing.
What is opto-mod technology in a Mu-Tron pedal?
Opto-mod is Musitronics' patented approach that uses light-dependent components, the same family of photo-couplers, optocouplers and vactrols found in the original Mu-Tron circuits, to control the signal. In the Tremu-Tron it provides what the maker calls classic, hi-fidelity attenuation without extra noise artifacts.
Is the Mu-Tron Tremu-Tron made in the USA?
Yes. Musitronics states that the Tremu-Tron A Stock is made in the USA, in the same rugged Mu-Tron enclosure as the rest of the current pedal line, and it carries a one year limited warranty from the maker.
Sources (4)
- Tremu-Tron A Stock, Musitronics Mu-Tron
- Mu-Tron Tremu-Tron Optical Tremolo + Boost, Pedal of the Day, 2022-01-26
- Beigel Sound Lab/Mu-FX Tru-Tron 3X Review, Premier Guitar, 2014-08-03
- Mu-Tron III+ Envelope Controlled Filter, Musitronics Mu-Tron
