Introduction: Cajon Hybrid (Αcoustic - Electronic Cajon)

By FS Woodworking

A cajón (Spanish pronunciation: [kaˈxon] ka-HON, "box", "crate" or "drawer") is nominally a six-sided, box-shaped percussion instrument originally from Peru, played by slapping the front or rear faces (generally thin plywood) with the hands, fingers, or sometimes various implements such as brushes, mallets, or sticks.
Cajones are primarily played in Afro-Peruvian music, as well as contemporary styles of flamenco and jazz among other genres. The term cajón is also applied to other unrelated box drums used in Latin American music such as the cajón de rumba used in Cuban rumba and the cajón de tapeo used in Mexican folk music.
Source:Wikipedia

Traditionally the cajon is an acoustic instrument but I wanted to take it a step further and make an electronic version of it, relatively easy to make and affordable. There are a few companies that make electronic cajones but with fixed drum modules and also very expensive. As a drummer I have two drumsets at home, an acoustic one and an electronic drumset. So I used the drum module of my electronic drumset to make my cajon pads come to life. Having a drum module, and using some wood I already had in my workshop I had to pay only 30€ for the whole project.

Tools:
About the tools: All the tools that I arrange here are just for reference on what I used for the construction of the instrument. Many people out there probably do not have all the tools that I have, ex. planer or shaper or radial arm saw, so I will try to give you alternatives on what tools you can use instead.

  • Safety glasses !!
  • Radial arm saw (You can use a circular saw, a jig saw or even a hand saw instead)
  • Tape measure
  • Pencil
  • Band saw (also here you can use a circular saw, a jig saw or even a hand saw)
  • Jointer and Planer (a hand plane should do the trick)
  • Router (This is a must!)
  • Drill Press
  • 25 mm forstner bit
  • 40 mm forstner bit
  • 10 cm hole saw
  • 20 mm corner round bit (As you can see in my video I used my shaper instead, although I highly recomend a router bit because its more accessible to anyone and much safer to use)
  • 10 mm straight router bit with a bearing on top (Also here in the videos I use my shaper but you can make a template or a jig and achieve the same results.)
  • Sander with 100 and 200 grit sand paper
  • Soldering Iron kit
  • Utility knife and scissors

Materials:

  • 20 mm thick plywood for the four sides (birch in my case)
  • 4 mm thick plywood for the front and back (birch as well)
  • (3x) pieces of any hardwood you can find 5.0 x 5.0 x 32 cm (I used white oak)
  • Wood glue
  • Guitar string
  • Guitar tuner
  • (3x) mono input jacks
  • (3x) 35 mm Piezoelectric transducers
  • Some wire (The thinest the better)
  • Rubber mat
  • (4x) rubber feet
  • Drum module
  • (3x) instrument cables 1/4 male - male
  • Water based wood finish
  • 20 mm screws
  • Sand paper 240 and 400 grits

You can also check the embedded videos for more details.

Attachments

Step 1: Prepairing the Four Sides

Take your 20mm plywood and cut two pieces 39 x 32 cm (H x W) and two pieces 25 x 32 cm (H x W). Pretty easy!

Once you have done that its time to make the rabbets. The exact dimensions provided in the plans I have attached! I made them using my radial arm saw, I lifted up the disk 1.0 cm from my table, so I can get one more cm cut. I kept cutting along the side of each piece until I had my rabbets done.You can also use your router with a straight bit to do that or if you have a table saw you can use a dado stack.

Step 2: Making the Corner Blocks

Get your hardwood and cut out four pieces 5.0 x 5.0 x 32 cm, square them using your planer or a hand plane and make two 1.0 x 1,5 cm grooves on each one of them 1.0 cm from the edge as shown in the pictures. Remember! I used my shaper here but you can do it just with your router and a 10mm straight bit. (Image 3) Once you have done that round the outside corner using your router and a round router bit. Again in the video and pictures I use my shaper.

Mark 1.0 cm from each groove as shown (Images 7, 8 and 9) and use a plane to bevel the inside edge at 45degrees. This is an optional step though, you can leave them square if you like, it doesn't really affect sound or appearance of the instrument.

Step 3: Assembling the Box

Before you assemble the box make three holes 3.0 cm appart from eachother using your 2.5 cm forstner bit to the one of the vertical sides of the cajon 2.0 cm from the edge. Those holes will accommodate the jacks for the instrument cables.

Once you have done that just glue all the pieces as shown (Image 3) and use some clamps to apply pressure on them while the glue dries (Image 4)

Step 4: Making the Jack Plate

Cut out the template you will find in the plans and transfer the shape on a piece of 4mm plywood. Cut the plywood and round the corners with a sander. Drill the holes for the jacks, attach the jacks and screw the plate on the cajon.

Step 5: The String Mechanism (The Frame)

We need to make a retractable mechanism that holds the string and the tuner. With a retractable string mechanism we can use the string when playing acoustic cajon and retract it when playing on the pads, so the buzz from the string on the front panel is reduced.

We need to make a 41.0 x 25.0 cm frame out of 2.0 x 2.0 cm wooden pieces.

So cut 2 pieces 41.0 x 2.0 x 2.0 cm and two pieces 25.0 x 2.0 x 2.0 cm. You can assemble the frame any way you like and feels more comfortable for you. I have used the mortise and tenon joint technique. It gives a very strong joint and if you use some screws to secure it, it gets even stronger.

Step 6: The String Mechanism (Tuner, String and Nuts)

Once you have finished making the frame, its time to add all the components that make the mechanism functional.

Take a guitar string (I used the "A" string, it is the second string) and pass it through a 3 mm hole on the lower right corner of the frame , 3 cm from the edge. Now pass it through a 8 mm hole in the middle of the upper wooden piece of the frame, around a nail and back through the hole again. Pass it through a second 3 mm hole on the lower left corner of the frame and attach it to the tuner. Now the tuner must be attached on a piece of 20 mm plywood in order to be strong and functional. 3 small pieces of hardwood will help reduce wood tear out while tuning. In the end you should have something like this.

Step 7: Attaching the Mechanism on the Cajon

Use two 30 mm hinges and 16 mm screws to attach the frame inside the cajon. The guitar string must touch on the front side at all points. Now on the right side of the cajon cut a slot so the bolt can pass through. This bolt is used with a wingnut and locks the wooden frame in place.

Step 8: Front and Back Sides

For the front and back sides I used 4 mm birch plywood. The dimensions provided in the attached plans. Cut the two pieces and round the corners a little bit.

Step 9: The Pads

For the pads I also used 4 mm birch plywood and some pieces of a rubber mat. The pads are 13 x 8 cm each. With a 40 mm forstner bit drill three holes 10 mm deep into the plywood. These holes must be under each pad and in the center of each pad. Now drill a 8 mm hole in the center of the 40 mm holes just to feed the piezo wires through them. Now cut 3 13 x 8 cm pieces of the rubber mat as shown on the pictures above.

Step 10: Assembling and Attaching the Pads on the Cajon

Use some construction adhesive or contact cement to attach the wired piezos under the pads. Feed the piezo wires through each hole, add a rubber mat piece under each pad and secure them on the cajon using some screws.

Step 11: Soldering

Solder the wires coming from the piezos on each jack. See the diagram here.

Lastly you can cut some pieces of plywood and use them to tidy up the cables inside the cajon as shown on the pictures above.

Step 12: Final Steps

Use a water based varnish to finish the cajon. I used it on everything, back and front sides, on the cajon box, on the jack plate and the pads. Two coats are fine. Now assemble everything and you are good to go!

The building process is now finished. Now the only thing missing is to connect the cajon on a drum module and start playing. I will upload a video on my Youtube channel later this week. Please check it out to see how it is connected to the module and what sounds it can generate!