Do It Yourself

Build Your Own Maestro Boomer 2

  • By Nicholas Kula @tonereport
  • November 09, 2016

It may surprise some readers to know that wah pedal was originally developed for trumpet players, a fact usually discovered when one sets out to discover what recordings Clyde McCoy played guitar on. Much ado has been made about McCoy’s involvement with wah circuitry, so many of us figured he had to be a legendary shredder. However, shortly after a look into the man’s musical history, we discover that he’s actually a celebrated trumpet player, and it is to brass and wood instrumentalists that wah was originally marketed. Eventually, this gave way to electric guitar and rock music was all the better for it.

The first wah pedal was the Cry Baby, mercilessly duplicated overseas because the Thomas Organ Company failed to do so. As such, it’s been cloned, re-cloned, then re-cloned again, resulting in hundreds of variants that all follow the same basic topology. Only a select few wahs deviate from this circuit, usually omitting the high-priced toroidal inductor in favor of different filter types that still sound very wah-like when manually swept. These deviators include the Mu-Tron C200, Colorsound Wah, Tychobrahe Parapedal, Korg Mr. Multi and a few others.

However, most other wahs that exist are riffs on this particular model. Maestro, not to be outdone, needed a wah in its product line and created two: the Boomerang and the Boomer 2. Fortunately, Maestro wasn’t comfortable cloning it straight away, instead refining the circuit, and the result was my favorite vintage inductor-based wah.

Unfortunately, cloning the Boomer 2 is quite a feat for a few reasons. Firstly, there are a couple weird parts, most notably a 6uF electrolytic capacitor and a 25k potentiometer. Most wah potentiometers are equipped with a mechanism that allows for foot control. Because they are engineered as drop-in replacements for Cry Baby pedals, they all come in the same value—100k. Secondly, wah parts are just plain expensive. Empty wah shells start at 45 dollars, wah pots start at 17, and the toroidal inductors start at 15. At this point, you’re 77 bucks into the wah, not counting other parts and labor. Add it all up, and you start to wonder if it’s worth it.

Fortunately, we’re going to build a wah in a regular enclosure. As a bonus, we’re including three common wah mods, such as Q, bass response and gain. As another bonus, we’re going to add an expression jack where you need only a 25k-equipped expression pedal such as a Mission or Ernie Ball. Without the expression plugged in, you can use it as a cocked-wah sound, or a really awesome overdrive by cranking the gain control. It’s awesome, and it will soon be yours.


First, the disclaimer:

Now that all the legalities are out of the way, let’s build that circuit board!

Parts you’ll need:


1x 1k

1x 8.2k

3x 10k

1x 56k

1x 820k

1x 1.5m


1x 10nF (0.01uF) film

1x 47nF (0.047uF) film

1x 100nF (0.1uF) film

2x 1uF film

1x 4.7uF electrolytic

1x 6uF electrolytic (in my layout I use a 5uF and 1uF in parallel. You can probably get away with 1uF and 4.7uF or two 3.3uF.)


1x 1kB

1x 25kB

2x 100kB


2x 2n5088 transistors


1x 500mH toroidal inductor (I used a red Fasel)

1x piece of stripboard (Veroboard) cut and drilled to spec in the diagram

4x potentiometer dust caps (optional)


Ok, let’s go!

Step 1: Place resistors in specified positions, bend leads outward, solder and clip leads. Save the leads.

Step 2: Using those clipped leads, form the jumper wires. Note that one of the jumpers is quite long, so you may have to use a piece of wire. Save just one more lead.

Step 3: Insert the capacitors, bend leads, solder and clip. I had low-profile capacitors so I did them all at once.

Step 4: Insert the transistors, bend the leads, solder and clip.

Step 5: Insert the inductor. There is no polarity issue here, though most schematics would have you believe otherwise. Solder and clip the lead nubs.

Step 6: Solder all wires to the board, and solder those wires to the pots when applicable.

Step 7: Solder wires to the wah pot, but don’t connect them to anything at the moment.

Ok, that’s that! Now it’s time for the enclosure!

You’ll need:

1x enclosure, preferably 125B or bigger size, drilled for input, output and expression jacks, DC power, LED, four knobs, one toggle switch and footswitch

1x 3PDT footswitch

1x LED

1x LED bezel (same size as LED)

1x 10k resistor (for LED)

1x SPDT toggle switch

2x 1/4-inch mono jacks

1x six-lug switched stereo jack

1x DC power jack

4x knobs of your choice


Alright, let’s do it!

Step 1: Mount the toggle, all jacks, LED in bezel and footswitch.

Step 2: Using the last saved lead, run it between lugs 4 and 9 of the footswitch. Solder lug 4. Insert the negative LED leg into lug 1, and attach the resistor to the positive LED leg, then attach the other end of the resistor to BOTH positive power lugs. Solder only one positive power terminal. If the LED legs aren’t long enough to reach, use wires.

Step 3: This is where we ground the enclosure. The way I have it wired affects the sweep of the wah with expression (to fix it, both sides of the stereo jack must be individually grounded). Run a wire from footswitch lugs 2 and 6 to the sleeve lug of the stereo jack and solder the footswitch lugs. Run a wire from one sleeve lug to the other, soldering the first one. Then, take turns soldering one wire to the next ground point and soldering the previous lug, until all ground points (jacks, DC power and switch) are wired together. Leave the final point unsoldered.

Step 4: The pots will have tiny metal tabs on them that prevent proper mounting. Snap these off with pliers and mount the board AND the wah pot. You may need to do some experimenting to find out which side of the stereo jack needs the pot wires and which side needs the board wires in order for expression to work properly.

Step 5: Attach board wires to their appropriate places, including the stereo jack, ground wire and toggle switch and footswitch connections. Finally solder the last ground point once you feed the ground wire to it.

Step 6: Solder input and output tip lugs to the footswitch. Solder lug 9 of the footswitch now that the two wires are in place.

Step 7: You’re done! Feel the funk!

So, what does it sound like?

Well, it sounds like a Maestro Boomer 2. Because the “bass” control also messes with the input resistor, you have to carefully adjust both it and the gain control to really make the pedal pop. When the gain control it dimed, it creates a fantastic “wah-verdrive” sound that has to be heard to be believed. That said, the sound is great on the whole. The way I had the expression jack wired turns the expression control into a “wah swell” just like the old Mu-Tron C200. It handles dirt exceptionally well and the cocked wah tones sound like a real wah, because it is. Here’s a clip of Andy giving it what for.



Until next time, up the irons!

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  1. Thermionic Studios

    Nice article, but the notes about the pedigree of the Clyde McCoy Wah are inaccurate.  Jim Dunlop put together an online movie with many performers, but also included Brad Plunkett (who invented the wah at Thomas Organ) along with Del Casher (who convinced Thomas Organ President Joe Benaron that the wah was a guitar effect, not a trumpet effect).  It’s not online anymore but can be found on YouTube:

  2. barrett

    where do you solder the input and output jacks to the toggle switch? the end of this build log got really complicated as you became less descriptive. bummed i couldnt get it working and got a pile of parts now.

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