I’ve come across a guitar tool that can accomplish a whole bunch of jobs for a small amount of coin and I thought I should let you know about it. While I initially pursued it for a couple of particular applications, it soon became clear that this is one of those devices that is extremely useful and flexible and can come in handy for hundreds of small but vital applications.

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Actually, the Micro Amp and I go way back, as in 'w-a-a-a-ay back. My first exposure to it came when I was given an original MXR Micro Amp by my brother at the beginning of the ‘80s and it became a foundational part of my rig. I had a Traynor medium-gain amp that needed what Nigel Tuffnel would call that “little push over the cliff” to become sweet. Fifteen years later when I sold the amplifier and I thought I wouldn’t need Micro Amp anymore, I sold it in a vacuous moment. Surprise! Ever since I’ve repeatedly had needs that the Micro Amp would have filled. Now, the original Micro Amp wasn’t perfect, but back then guitar effects were pretty rough and ready and by contrast it was classy. It remained the best thing going for about twenty years before the boutique market supplied newer options. I've seen original examples selling for over $200 and the black market has begun making clones, so I suppose they must have had something on the ball. But recently, the MXR custom shop decided to refresh their original design with a new version that added some little tweaks that seemed to promise even more quality and utility, so it came time for me to investigate. Of course, we’ve all become accustomed to companies “upgrading” their classic designs, only to discover that the charm of the original was somehow lost along the way. Don't you hate that? I was wary of this tendency and paid special attention as I evaluated this new design.

What is the Micro Amp+?   It is a clean boost pedal featuring true bypass and a simple bass and treble EQ.
That sounds pretty drab. What can you do with it?

Clean sounds: You can “cook” a tube amp for a wonderful bloom of overtones. Here is how you do it with a clean boost in front of a tube amplifier: First, get your basic clean sound with the boost out of the chain. Then, kick in the boost and push up the gain until the preamp distorts. Finally, back off the gain until the amp just cleans up. You’ll notice more character and overtones in your sound because the amp is generating even-number harmonics in the soft zone of distortion. Also, if you adjust your gain just right, just a little higher, you’ll be able to go in and out of grind by increasing and decreasing the power of your picking attack.

Dirty sounds: You can use a clean boost to drive the front of an amp that is on the edge of distortion right off the cliff and can switch it in and out via footswitch. Because you will be driving the first tube gain stage with the clean boost rather than driving the second tube stage with the first, you will probably also hear a different character to the distortion as well.

Lead sounds: You can push up the gain on a medium-gain amp and raise the volume for leads via a footswitch. With the EQ you can also prevent some of the bass sogginess or treble ice-pick that might result. There's plenty of gain to allow you to push a single-coil guitar's sound up to that point where it becomes phat and sustainy.

Channel switching: On your two-channel amps you can add a third channel with its own separate gain and EQ controls to allow clean, crunch, and drive sounds for ultimate flexibility.

Guitar switching: You can set up your rig to switch between single coil pickups and humbuckers rapidly and match levels and basic tones.

And on and on...

The pedal is packaged in the familiar, sturdy, one-space MXR enclosure with the familiar black knobs, heavy-duty footswitch, and cone-shaped input and output jacks. Power is 9vDC via battery, accessed by unscrewing the baseplate, or via the usual barrel jack. The color is very much like the original except that a little pearlescence has been mixed in for fun. The red "engaged" LED has been retained from the second edition of the M133 Micro Amp.

Recently, the electronic elves from the Dunlop Custom Shop, specifically Bob Cedro of Scholz and Rockman fame, undertook to upgrade the quality of a couple of the classic MXR pedals. With the Micro Amp, Bob redesigned the gain circuit and added a two-band EQ. The original M133 exhibited a tiny bit of high frequency roll off and some frequency response non-linearity. That roll-off was there whether the pedal was switched in or out because it lived in the buffer amp and the pedal wasn’t a true bypass design. Firstly, on the CSP233 Micro Amp Plus the Custom Shop added true bypass. Secondly, even with the EQ controls centered, that roll-off is a thing of the past. Based upon a new, low-noise integrated circuit, this new design has a much flatter response (+/- 0.75db, 20-20kHz). Thirdly, the new design also greatly reduces the background noise to far below that which was exhibited by the original as well (to -87db). And finally, they also added the elegant, subtle EQ circuit mentioned above to round out the pedal.

First off, with the EQ knobs centered the pedal is virtually transparent in tone. Amazingly so, in fact. As you use the pedal, one of the extremely attractive design characteristics of this unit is the use of very gentle tapers on the EQ controls. Those tapers make the controls less sensitive around the null areas and more so towards the ends of their travel so it is possible to easily center up the controls and have them virtually disappear from the signal. Then as you move away from the nulls, the controls progressively begin to “bite” and do their thing. The Gain control works similarly: there’s plenty of subtle travel down near the bottom, allowing you to use the Gain control for fine gain makeup. That is important if you want to match the bypass level when you use the EQ to roll-off frequencies. That capability brings up one of my favorite uses for this pedal and the one that finally drove me to throw down the extra pesos for the new Micro Amp Plus: I use this pedal to cleanly reduce the “woof” from humbucking pickups when played into a Fender 5E3 Tweed Deluxe. The Tweed Deluxe was clearly designed to match the frequency spectrum of Fender’s single coil pickups and it does so marvelously. However, with their increased gain and rolled-off high end, humbucker pickups can make the amp sound a bit “woofy.” This pedal allows you to gently roll out that woofiness without negating all the wonderful interaction between the guitar and the Deluxe’s preamp. One of my first tests for the pedal was to plug it up with a Deluxe and back off an ES-335's volume control to see how it reacted. It felt just like plugging in directly and there didn't appear to be any strange frequency effects, either, as I rolled back my guitar’s volume control.

So, with this pedal’s custom shop refresh, Dunlop/MXR have successfully updated what was already an extremely useful design in all the right ways. With the addition of the EQ, they’ve turned it into a virtual Swiss Army Knife of gain and tone. The sound quality of this version easily exceeds the original, taking it far into the boutique pedal realm. As a result, the MXR Micro Amp Plus is the sort of tool that should probably live in every serious electric guitarist’s toolkit.

Input Impedance: 1 Megohm
Output Impedance: 470 Ohm
Maximum Output Level: +7dbv
Noise Floor: -87db (A-weighted, Gain at maximum clockwise position, Bass and Treble at mid position)
Tone Controls
Bass: +/-14db at 33 Hz **
Treble: +/- 11 db at 8.4 kHz
Gain Control: +.05 to +26 db
Frequency Response: 20hz to 20khz +/- 0.75 db
Bypass: True Hardwire
Current Draw: 6.5 mA
Power Supply: 9 vDC
Street price: $119.99

** The user's guide states that the bass frequency is 33 hz but it sounds more like 330 hz to me. Could be a typo.

The pedal
User’s guide
Warranty card (can be registered online)
Dunlop Electronics 2013 Catalog