The Luna Mod Looper

Weekend Project

Weekend Project

This project is part of RadioShack's The Great Create.

A simple handheld synth and looper box that generates intriguing sonic rhythms.

  • Author: Brian McNamara
  • Time required: 1-2 weekends
  • Difficulty: Moderate
  • Add Note x

The Luna Mod is an easy and fun instrument that will have you making great-sounding loops in no time. Rather than sampling input like a traditional loop station, the Luna Mod synthesizes its own sounds, and you play it using two knobs and one button.

I based the Luna Mod on the Wicks Looper, which I sell on Etsy, but it’s designed to be even simpler to build and play, without any complicated functions that would never get used. One knob controls the sound generated, the other controls the tempo of the loop, and the button writes the current sound into the ongoing loop. The variety of sounds you can get from these three controls is amazing.

You don’t need any special or expensive tools to build the Luna Mod, and it was designed for hackability. Its handy, built-in programming port lets you easily upload new firmware to the microcontroller chip, in order to change the sounds the instrument produces and which variables are tied to which controls.

Check out more Weekend Projects.

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Add Note Edit Step 1 — Populate the circuit board  ¶ 

  • Take a 26x16-hole piece of stripboard (use a sharp hacksaw as necessary to cut to size, then sand the edges smooth). The copper strips should run the long way.

  • Cut, strip, and solder 13 solid-core jumper wires between the following points on the board: (5,1 to 5,3), (5,15 to 5,16), (7,10 to 7,11), (7,13 to 7,15), (11,5 to 11,11), (13,5 to 13,7), (14,4 to 14,9), (16,8 to 16,14), (17,9 to 17,11), (19,10 to 19,12), (19,14 to 19,15), (21,9 to 21,14), and (22,8 to 22,13).

    • To identify holes on the board for placing components, I use grid references of the form (x,y), where (1,1) is the top left hole of the non-solder pad side, and the board’s long edge and copper strips run along the x-axis.

    • On the shorter jumpers you can remove all the insulation on the wires.

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Add Note Edit Step 2 — Populating the board  ¶ 

  • Turn a sharp 1/8" drill bit by hand to make breaks in the board’s copper traces at these points: (5,12), (8,3), (8,11), (8,13), (11,3), (14,11), (14,12), (14,13), (14,14), (16,3), (17,14), (17,16), (19,8), (20,12), (24,6), (24,10).

    • Remember to count the x-coordinate from right to left when the board’s copper side is facing you.

  • Solder the resistors onto the stripboard: 1kΩ (18,12 to 18,16) and (25,12 to 25,16); 10kΩ (2,12 to 2,16), (9,7 to 9,14), (10,3 to 10,13), and (21,3 to 21,7); and 22kΩ (3,12 to 7,12).

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Add Note Edit Step 3 — Adding additional components  ¶ 

  • Solder in the 8-pin IC socket with Pin 1 at (12,11) and Pin 8 at (15,11).

  • Solder in the 2 caps: 10nF (23,12 to 23,14) and 100nF (20,14 to 20,16).

  • Solder in the voltage regulator, Pin 1 to (3,5) and Pin 3 to (3,3).

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Add Note Edit Step 4 — Installing the LEDs  ¶ 

  • Trim the LED leads to ½" (14mm) to keep them long enough to poke up through the panel, but keep track of which legs are positive (anode, with the longer leg) and which are negative (cathode, shorter and marked by a flat part in the plastic).

  • Solder one LED with its (+) leg at (9,3) and (–) leg at (9,4), and the other with (+) at (18,3) and (–) at (18,4).

  • The on/off toggle switch legs are too wide to fit directly into the PCB holes, so use a 1/16" drill bit to extend the holes into small slots at (14,1), (14,2), and (14,3).

  • Fit and solder the switch into place.

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Add Note Edit Step 5 — In go the pots  ¶ 

  • For the potentiometers, use the 5/16" bit to enlarge the holes at (1,6), (1,10), (26,6), and (26,10). Locate Pin 1 on each of the pots; it’s the rightmost pin as you face the pins with the pot shaft pointing up.

  • Fit the pots’ mounting tabs into the enlarged holes with Pin 1 of one at (4,9) and Pin 1 of the other at (23,7). Solder into place.

  • For the programming socket, cut 3 wires, ideally of different colors, about 3½" (or 9cm) long. Solder one end of each to (1,11), (1,12), and (1,13).

  • Remove the 1/8" stereo jack cover, slip it over the 3 wires, and solder the wires to the jack’s contacts for the plug’s sleeve (inner), ring (middle), and tip (end), respectively. Replace the cover.

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Add Note Edit Step 6 — Wiring the pushbutton and audio jack  ¶ 

  • Solder 2 wire leads for the pushbutton about 7" (or 18cm) long at locations (1,14) and (1,15).

  • You’ll solder the pushbutton to these 2 loose wires after fitting it into the front of the panel.

  • Solder 2 wires about 7" (or 18cm) long to the PCB at (26,12) and (26,14). Solder the other ends to the panel-mount mono audio jack’s tip (signal) and sleeve (ground) contacts, respectively.

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Add Note Edit Step 7 — Finishing up the electronics  ¶ 

  • Solder the 9-volt battery clip to the board, red (+) to (1,2) and black (–) to (1,4).

  • Plug the Picaxe 08M into the IC socket with pin 1 at upper left, nearer the LEDs.

  • The circuit board is now finished and ready to fit into the control panel.

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Add Note Edit Step 8 — Building the case  ¶ 

  • Using 3/8" board, cut two 5½"×1 5/8" side pieces and two 2½"×1 5/8" end pieces. (Using 8mm boards, cut pieces 140mm×40mm and 65mm×40mm.)

  • For the base, cut a piece 5 7/8"×3 5/8" (or for 8mm wood, 150mm×90mm.)

  • For the lid, cut a piece 5½"×3¼" (or for 8mm wood, 140mm×82mm.)

  • For the control panel, cut a piece 4¾"×2½" (or for 8mm wood, 124mm×65mm.)

  • Use sandpaper and a sanding block to put a small bevel around the top edges of the base and lid pieces.

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