MXR M133 Micro Amp Review

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Clean boost pedals are one of the simplest but ultimately helpful tools you can have as a guitar player. The idea behind a clean boost is to add more gain in your signal chain. Why would anyone want that? Well, there are plenty of reasons. To name a few of the most common ones, a clean boost can push your tube amp into that sweet spot without affect volume. It can also match the volume of different guitars, and lastly, it can give your tone a whole lot of girth that wasn’t available before. The MXR M133 Micro Amp is one of the better pedals of this type.


Design and layout of MXR M133 Micro Amp is incredibly simple. They have used their standard mini chassis for this model. For example, if you were to look at controls, you would find just one knob labeled as Gain. That is all there is to it. Its finish is also pretty simple. As you probably know, MXR is not too big on complex graphics and similar stuff. Instead, they pretty much color code their pedals while using the same logo/labeling pattern they have come up with ages ago. In case of MXR M133, it’s a beige color with a slightly rough texture.

Feature Pick

Mxr M133 Micro Amp

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Build Quality

Good looks might be important to some, but build quality is what you really want to know about. MXR’s pedal bodies were always known to be fairly rugged. After all, it is a die cast piece of pretty thick metal. Putting a serious dent on that would take much more than your feet can do. During a brief period of time, MXR had some troubles with their switches. Whether they used a bad batch or they sourced this component out to a bad manufacturer is unknown, but those switches were terrible. The stuff they use today is much better and goes in line the overall reliability of their pedals. You can easily have MXR 133 on your pedalboard, use it every day in harsh conditions, and have it work next time you push that foot switch. This is a professional piece of kit in every sense of the word.

MXR M133 review


As we have mentioned before, there aren’t many features on MXR M133 Micro Amp. The pedal features a single knob, an input and an output. The only other details worth mentioning is power management. You can use a 9V battery or a power adapter to keep this puppy fed. Aside from that, MXR M133 Micro Amp is one of the simplest and most basic pedals you will run into. As are most clean boosters out there. Let’s talk about its performance as that part of the equation is much more interesting anyway.



Clean boost are a powerful tool to have. They are very versatile, although the type of versatility we are talking about is a bit different. MXR M133 Micro Amp perfectly describes what a proper clean boost pedal should be like. The gain it infuses into the signal is extremely pure. You can easily use it on a clean channel and get no negative side effects. Speaking of which, if you were to pair the M133 with a proper tube amp, it could push those valves into that subtle overdrive.

However, the real fun starts when you pair this pedal with a good dirty channel. All you have to do is find a value of gain that isn’t an overkill and you are in for a world of fun. The first thing you will notice is the amount of added girth. Leads feel much thicker without there being more distortion. You just feel more weight to the tone. One good way to isolate the effect is to drop a couple of blues riffs. Rhythm is not the only area that gets better. Arguably, solos have much more to gain from a proper clean boost pedal.

Another thing that clean boost does, especially MXR M133 Micro Amp, is shaping up the performance of passive pickups. By hooking this pedal into your signal chain, you can get passive humbuckers to sound fairly hot, almost resembling an active setup. In other words, you can gain access to that active tone without losing any of the expression ability a set of passive pickups inherently have. In the right set of hands, this can turn out to be pretty effective.

If these words aren’t enough, watch this video demo of the MXR Micro Amp Boost Pedal from ProGuitarShopDemos to get a better feel for how this pedal sounds.


At the end of the day, MXR M133 Micro Amp is a much more impressive pedal that it appears to be. In the world of sledgehammers, it is a fine tuned scalpel. Many guitar players, especially those who are new to the world of guitar effects, have a hard time understanding what’s so great about clean boosters. If you are in that group, do yourself a favor and try this pedal out. It might just be the missing link you were looking for. In fact, Jack White’s discography offers all the proof you will ever need regarding what clean boost pedals can do. He has virtually mastered this particular effect, making it an integral part of his very unique tone.

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