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MXR M-133 Micro Amp Review

Updated on June 11, 2013
The MXR MIcro Amp is a clean boost pedal designed to drive the front end of a tube amp into saturated distortion by pushing the guitar signal's volume.
The MXR MIcro Amp is a clean boost pedal designed to drive the front end of a tube amp into saturated distortion by pushing the guitar signal's volume. | Source


Standard Retail Price: $79.99
Typical Used Price: $60 to $40

Controls: Gain
Power: 9-volt battery or Boss-style adapter (not included)

Famous Users: Albert Hammond, Jr. and Nick Valensi (The Strokes); Jesse Valenzuela (Gin Blossoms); Edwyn Collins (solo)
Further Information: The Official Dunlop Manufacturing Website

Overall Value

4 stars for MXR Micro Amp Boost Pedal

First Impression

MXR's pedals have a reputation for being at least as well-constructed as Roland's Boss units. That is to say, they're like miniature metal bricks that could be dropped from several stories above ground, plugged in and would probably still work. The chassis is simply constructed and small enough that it won't take up too much of the valuable real estate on your pedal board, and the single control knob tells you at a glance that operation will probably be a no-brainer.

Albert Hammond, Jr. (left) and Nick Valensi are noted users of the MXR Micro Amp. They utilize the pedal to achieve their saturated yet articulate guitar tones that form the foundation of the Strokes' sound.
Albert Hammond, Jr. (left) and Nick Valensi are noted users of the MXR Micro Amp. They utilize the pedal to achieve their saturated yet articulate guitar tones that form the foundation of the Strokes' sound.

Ease of Use

It probably goes without saying at this point that the M-133 is dead simple to use, but just in case you haven't already guessed, I'll spell it out for you: the M-133 is dead simple to use. However, I'll offer the disclaimer that it has many more functions than just the obvious one, and despite having only one control, there's quite a range of sounds to be found when using this pedal with a decent tube amp.

  • The lone control knob is labeled "Gain." Turn it to the left to minimize the boost effect and achieve gain unity (where the volume of your guitar signal with the effect on is equal to the volume with the effect turned off). Dial the control knob to the right to increase the amount of volume added to the signal while the effect is on.

The pedal features a single input and output, too, meaning that connection is as simple as it's possible to get. A plunger-style button is easy to toggle with one's foot, and a bright red LED tells the user when the effect is activated and when it's disabled. This is about as straightforward as pedal design gets!


It's worth noting at this point that the Micro Amp is mainly useful in the context of playing live, specifically with a tube amplifier. It's not likely to add much to your solo practice or writing sessions (although if you practice or write at a fairly loud volume, you may find that stomping on this guy when you arrive at a song's solo section fattens your sound a lot, which can be very inspiring) and when used in conjunction with a solid state or hybrid amp, you're unlikely to really be able to take advantage of the M-133's ability to add searing gain to an already-saturated amp sound.

Therefore, please bear in mind that "live performance" is the perspective from which the rest of this review is written, as I have never bothered to use this pedal in a recording context--since two different guitar signals recorded on different tracks can be blended to taste during mixdown, with levels raised or lowered accordingly.

MXR/Dunlop initially marketed the Micro Amp as a mere volume boost, and it definitely does a great job as such. As mentioned earlier, activating on the pedal as you play introduces a boost that is as subtle or extreme as you want it to be; as an added bonus, I can attest that I've never noticed any coloration to my guitar tone when using the M-133. Other boost pedals often introduce a mid-range "hump" that I, personally, usually don't mind. But it's nice to know I can use the MXR unit to get more of my sound, unadulterated.

A secondary function, per the manufacturer, is to slam the front end of a tube amplifier with extra volume to create even more saturated gain sounds than an amp is capable of producing on its own. Again, the M-133 Micro Amp excels at this, too.

Recently, MXR/Dunlop has been touting the pedal as a quick fix for guitarists who switch back and forth between, say, a Fender Stratocaster and a Gibson Les Paul during the course of a performance. Anyone who has utilized two instruments with different pickup configurations during the course of a single show is going to be intimately familiar with the problems posed by the volume discrepancy between single-coils and humbuckers. The Micro Amp does indeed make an effective solution; simply set the Gain knob so that stepping on the pedal brings the single-coil guitar's level up to match that of the humbucker-equipped instrument. Turn the M-133 off when you switch back to humbuckers.

Another great use for the M-133 is as a signal buffer. As any fan of effects pedals knows, the more stompboxes one lines up between your guitar and your amplifier, the weaker and less pure one's guitar signal becomes. There's some debate as to the actual cause of this problem, but there's really only one solution--which is to find a buffer to increase the volume of the signal before it enters the pedal chain so that a higher percentage of pure guitar sound reaches the amplifier after traveling through your effects. Putting the Micro Amp at the very start of your signal chain is a great way to buffer your sound, making this an invaluable tool for effects junkies who don't want to compromise their clean sound.


The MXR M-133 Micro Amp is a very easy-to-use pedal, but don't be fooled by the simplicity of its layout: there are a lot of uses to be found for this unit beyond its functionality as a straight-up clean boost, although the ability to dramatically increase your volume without coloring your tone is, by itself, worth the price of admission.

For guitarists who switch between multiple guitars with different pickup configurations and who may be driven slightly crazy by the volume drop between single-coils and humbuckers, the Micro Amp makes an inexpensive, easy-to-use and convenient solution.

I'd definitely recommend this pedal for anyone looking for access to a high-quality signal boost without breaking the bank.

Which way would you be most inclined toward using an MXR M-133 Micro Amp?

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