Stomp box, Cajon Hybrid

The original idea came to me after seeing mostly acoustic bands, that I've seen at festivals, with the bassist or guitarist also playing the rhythm, percussion part by means of a Cajon.

When looking for information about the Cajon themselves, because it just seem kinda simple boxes (the real ones aren't that simple and need a lot more craftsmanship than I posses.) I came across the stomp box, a mostly smaller box with an electric pickup element available for amplification.

After further searching, I discovered a mix of the acoustic Cajon and electric stomp box. This seemed to me a nice mix for a DIY project.

The chosen sizes are a result of the boxes containing my small guitar gear, the height I like for my footrest playing guitar or bass while sitting down and the size of available wood in my shed.

The things I have used:

Materials

3.5mm thick, hardwood plywood
210cm x 11.8cm x 18mm pinewood
Wood glue
35 x 4.0mm screws
15 x 3.0mm screws
4 plastic feet (small doorstops/bumps)
6.3mm jack-plug chassis-mount
Piezo electric element
Piece of 2 wire cord
Hotglue
Solder

Tools

Saw
Screwdriver
Pencil
Drilling machine
Drills (2, 4, 6 and 9 mm)
Forstner bit 30 mm
Countersink
Wire cutter
Soldering iron
Tape measure
Squared

Step 1: The Basic Frame

After cutting the plank in two pieces of 32 cm and two pieces of 20 cm long and the plywood plate in two pieces slightly larger than 32 x 24 cm

You get four pieces of pinewood as below, in the shape that I wanted to make the frame/sides.

on the longer planks, drawing the spot for the screw holes for the frame first. Making sure that the jack chassis mount and screws don't end up in the same spot. Creating "fun" things like shorts

Step 2: Jack Chassismount Hole

Because I wanted to have the plug on the side and my wood is relatively thick. There is a need for a bigger "sink" hole than is needed on the outside.

The chassis-mount used here needs really only one hole of 9 mm diameter. However the mounting thread is much shorter then needed for the wood thickness. By making one side of the hole a lot lager. making it able to hold the base part of the mount, and making the wood thickness thin enough for the chassis-mount. Another advantage of starting from two sides work is that you have less chance for ugly chipping.

(The size of the holes or drilling depends on your used chassis part)

First I made a pilot hole so I knew the exact point for the small and large hole for both sides.

After that with a power drill and the 30 mm Forstner bit, the larger part of the hole is made. (About 14 mm deep in the 18mm think wood). This can also be done with a wood spade bit, however, which has a much larger centering point which makes it harder to get a nice finish on the 9mm hole on the outside

From the other side I've drilled the hole with the 9 mm drill.

Step 3: Frame Construction

If you have more patience than I, and better or more glue clamps, this can be done without screws.
Also more beautiful corner connections are to do if you more ease of use and the right tools. (think of miter, tongues, and so on)

This shows that if I put the four sides together with glue and screws. I will get a more or less square box.

Here are the parts laying flat, with the screw holes drilled. Making it easier to get the screws straight and the wood not split or crack.

Gluing and screwing the four shelves together into a frame should be quite straight forward.

The frame will be glued on top of the plywood plate. This glued plate will be the strike plate of the the box

(The plastic bag is used to prevent accidental gluing my project to the wooden table. A precaution that I've learned from previous mistakes.)

Clamps and letting it dry for the night ...

This is the moment I had my biggest goof on this project. While clamping I failed to notice the movement between the frame and the plywood. I decided to continue on, and remembering to start triple checking for movement during clamping.

This photo shows the damage done with the clamping. It also shows that doing a quick cut of protruding piece with the saw, wasn't a good idea. Now I will need to sand the piece a lot more.

Step 4: The Electrical Part

To get the electrical current from the piezo element to the jack mount, you need a few wires soldered to both.

I have used hotglue to mount the piezo element to the tapping board. Putting it in the more or less middle of the plate, expecting the warmest, deepest sounds there.

Only one thing was clear for me after researching the boombox. The element used and the spot placed is hotly debated. Mostly based on taste for one kind of sound or another. To make it easier to experiment I've only used hotglue on the edges, making removing without destroying easier. Some sources were quite fanatic that it should be somewhere on the tapping board, others were sure that it needed to be on one of the sides. (Almost as fierce as the Windows, Linux and OSX discussion.) The only thing I know at this moment is, that I will need to experiment a lot to get the best sound possible for my taste.

I have seen a lot of different elements used. Like piezo electric elements, speakers, dynamic microphones, real guitar or bass elements. there are a lot of possible solutions.

Step 5: Closing the Box

The last plate is only screwed on the box screwed, not glued.
This enables replacing and moving the piezo element around. Also I made the sound hole in this board. This makes it possible to experiment with that too, without the need to rebuilt the whole box, just the plywood plate. An other but less important part in the decision for having the sound hole on the bottom is having cats who like tho play with threads or wire. Less chances of them getting there and breaking the electrical part of the box.

Marked the screw holes. Those are pre-drilled too, except the four corner ones. The feet I have available are a little wider then the thickness of the shelves used. There holes wouldn't be in the middle of them.

Because I didn't want to glue it, I choose to use relatively many screws (on the long sides 5cm apart and on the short sides 5.5cm apart)
And lastly the feet. Also marked and drilled, preventing splitting or tearing of the wood and making having straight screw easier.

and finally standing on its feet in the last photo...

Step 6: Finally

And the test setup:

Everything works as expected. the box sounds OK acoustic and amplified. As you see it's cat-approved too :)

(If I find someone who has rhythm and likes to be in a video, I will add that in a later stage)

Adding a small list of possible improvements.

When gluing. Be better prepared and careful, and check again (twice wasn't enough this time)
Adding a volume control. I think a control as used in an (passive) electric guitar would work well (500k ohm log)
in general, no in between quick fixes of goof ups. I really don't like sanding, especially now my sanding machine is broken
As suggest by RowanCant, other types of pickups, or even a combination of them.
a nice finish on the outside

Inspiration and motivation for this instructable for this project by:

Youtube woodworkers like Steve Ramsey and Matthias Wandel

Hack42 en instructables motivator Moem and others at Hack42