Mini MicroAmp Build

With each new pedal build, I try to focus on some aspect that makes it a new challenge or something new to learn. My first pedal build ever (about 18 months ago) was a boost pedal. I decided I’d build another boost: this one using the MXR MicroAmp circuit. I used the General Guitar Gadgets MAMP PCB, which in addition to selling the PCB sells entire kits and has excellent documentation1. Since it’s a relatively simple circuit and, therefore a fairly small PCB, I wanted to try to fit it into a “mini” enclosure (i.e., a 1590A format). This means having to really think ahead about aspects of the build so that everything can squeeze into such a relatively small enclosure.

The completed enclosure, including the mis-aligned hole for the input jack on the right side

The first thing is that this pedal format can’t utilize a battery for power; the pedal will be AC powered only. That’s fine as I don’t use batteries in any pedal anyway and only ever added a battery snap to that first pedal build. Secondly, the height of the components really matters. The taller components (generally, the capacitors) had to be bent over. For the electrolytic capacitors, I had to remove and replace a couple in order to facilitate this (I had planned ahead otherwise – as my sketched notes on the wiring diagram shows below, but I am just so in the habit of soldering the completely vertical I forgot!). In the end, the tallest component off the PCB was the integrated circuit (IC), as it was mounted in a socket. This way I can potentially swap out ICs in the future. Speaking of ICs, I went with a low-noise TL071 op-amp (in place of the original pedal’s TLo61 – which consumes less current but, again, I’m not using a battery so I don’t really care about that). The only other modification I made to the GGG circuit was that I swapped out a 10MΩ in place of the 22MΩ pull-down resistor (R1). Really, any fairly large (<1MΩ) resistor value will do here and 22MΩ are a little harder to find.

The completed wiring. This was a tight fit! Notice all the taller capacitors look like a strong wind came through.

Lastly, the arrangement of the larger off-board components such as the footswitch, jacks, LED bezel, and pot really came down to millimeters. I had to use calipers to measure every last item and meticulous sketch it out on a printout of the enclosure. I still managed to mess up drilling one of the jack holes (I located it 1/2 the diameter off, which s about the worst place to mess it up!). I was able to re-drill the hole thanks to having a drill press and some clamping blocks. It’s a bit ugly and the jack’s nut is a bit crooked, but it worked out fine.

Re-drilling a hole for the output jack. Drill press & clamps absolutely required to fix this sort of bone-headed mistake.

The pedal works great. I mean, it’s about as simple an effect as you can get. It simply takes the guitar signal and makes it a lot louder (probably around the order of 20-25db). I’m pretty pleased with how clean the wiring worked out, as well.

My build cost around $27 for the parts I had to purchase. That’s not including resistors, capacitors, diode, and LED (nor hookup wire and solder), all of which I already had in my parts bins but would run you around $3 in total. I also had to pay around $9 in shipping. The PCB from GGG for was about $3.50 to ship. I bought parts for several builds at once in a large order from Mammoth Electronics (my parts supplier of choice), but smaller orders from there tend to ship for around $5. They have high-quality powder-coated enclosures for really great prices, along with generally good prices on other parts and kits. So, in total, this build is roughy around $39 in cost (and I still haven’t added any artwork, so consider what slide decal or other format might cost).

That being said, unless you really want to build your own, I would not recommend this build to anyone else. You can purchase a TC Electronic Spark for about $35 used on Reverb.com (plus shipping) right now. It has the exact same size as my build, but has their amazing non-latching (relay) footswitch and essentially the same amount of clean boost. If you don’t care about size, you can purchase a used MXR MicroAmp for around $49 on Reverb (plus shipping). Both of those are solid choices if you really just want a boost pedal and are less interested in practicing your soldering skills or learning how to layout a small pedal form factor. And honestly, as much as I think this pedal sounds great so far, those probably sound even better and have less noise at full gain.

But overall, I’m pleased with this build. On the clean channel, it just gets louder without adding anything else noticeable. Best of all: with the knob set to about 3 o’clock, it makes my Blackstar HT-5R head’s gain channel absolutely breathe fire!

  1. I think I could have pretty easily build this circuit on perfboard, but probably not to fit in the this small of an enclosure. So for a bit more cost I opted for the PCB, which has a fairly small footprint. []

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