Radio Music Mk2 Build Guide ←

Radio Music is a 4hp Eurorack module that you can build yourself in an hour or so. The video above shows a complete end-to-end build with full instructions.

The single PCB is pre-populated with 90 tiny components. Your job is to attach the power header and interface elements: pots, buttons, sockets, LEDs and the SD Card holder.
It’s not a difficult project, but the density of the board means it probably shouldn’t be the first thing you ever solder. If you also bought a Radio Remote, build that first.
A few parts of the build are slightly counter-intuitive, so please watch the video or read the text below carefully. If anything is unclear, contact [email protected], send photos.
NB: This is the build guide for Radio Music kits bought in 2026 and after. For older kits, use this version.

Once you’re finished, use the Radio Music testing guide to check the controls, sockets, LEDs and SD card playback.

What you need to know about soldering before you start ←

To build Radio Music you’ll need to make about 45 through-hole solder joints.
Your joints don’t have to be perfect, but for the module to work, they should all look like one of the ‘OK’ joints in the image above.
Here is a good seven-minute video introduction to soldering from Curious Inventor.
I recommend Adafruit’s fantastic Guide To Excellent Soldering. The image comes from the common problems page.

Build Guide ←

I recommend watching the real-time build video above, which talks through all stages of building Radio Music mk2 in detail. This guide provides step-by-step guidance.

Tools required: solder, soldering iron, diagonal cutters AKA snips AKA side-cutters, masking tape. A Digital Multimeter is always helpful for checking for bad solder joints and continuity. Thonk sell a range of inexpensive tools.

1. Introducing the PCB ←

Take a look at the bare PCB.

This is a very dense board with many tiny surface mount (SMD) components already attached. The board has been tested at Thonk, and the microcontroller is already programmed.

The Front side is the side with all the components - including the USB-C socket which pokes through the front panel.

The Back side is the side that faces into the case. It has no populated SMD components but will have the power header connected to the ribbon cable.

Front of the programmed Radio Music PCB before build — Programmed PCB, front side.

Back of the programmed Radio Music PCB before build — Rear side: headers go here.

2. Attach the power header ←

Take great care with this step as it is critical and hard to fix later.

The power header pins are quite large, and the 6 central pins are connected to large ground planes, so require a little bit more heat than usual to solder them. However, if you apply too much heat, the pin can melt the plastic and drop down - requiring a bit of fiddling to get it all aligned.

To hold everything in place I use the four Thonkiconn sockets to lift up the board over the power header and a strip of masking tape to hold the board in place. The video shows my technique for doing this.

Then solder just one pin and check the power header is flush and well aligned. If not, re-heat the pin (make sure you’re not holding that pin with your finger!) and slot it into place.

At this stage, you can also add the optional 4-pin expansion header if it comes with your kit. It won’t do anything until I think of something to do with that header.

Radio Music PCB with rear header placed — Solder one point on the power header before checking alignment.

Side view of the power header sitting flush on the Radio Music PCB — Check the header is upright and flush before committing.

Rear headers soldered on the Radio Music PCB — Then solder all the pins.

3. Fit pots, sockets and LEDs without soldering ←

The next step is to put the pots, sockets and LEDs into place, before soldering them.

We’ll come back to do the button and SD Card holder later. If you’re super confident you can do it all in one step.

Pots: These are slightly unusual pots with 5 pins and two legs. They’ll only mount in one direction but make sure all pins are straight and going into the holes

LEDs: LEDs must be oriented correctly. Each LED has one long leg and one short leg. The Long leg goes into the hole marked with a + symbol. There are 5 LEDs, one goes next to the Reset button and is very close to the expansion header.

Sockets: Remove any nuts from the sockets before installing them.

DON’T SOLDER YET.

Radio Music PCB with the pots placed before soldering — Pots placed, not soldered.

Radio Music PCB with jacks and pots placed before soldering — Jacks added, nuts removed.

Radio Music PCB with pots, jacks and LEDs placed before soldering — Pots, jacks and LEDs placed before fitting the panel.

4. Use the panel as an alignment tool ←

Place the front panel into place. Put a nut onto one of the pots and two of the sockets. Don’t worry about the LEDs yet.

Check the panel and the PCB are parallel and aligned. Give them a squeeze!

Now add some masking tape and push through the LEDs to keep them aligned to the panel. If you prefer, you can also push them straight through - it’s purely aesthetic.

DON’T SOLDER YET

Radio Music panel fitted over the loose controls — Panel fitted before soldering.

Radio Music panel held with jack and pot nuts — Use nuts to hold the panel in position.

Radio Music LEDs taped in place from the front panel — Tape keeps LEDs flush to the panel.

Back of Radio Music PCB while LEDs are taped in place — Back view before soldering one point on each part.

5. Check everything, then solder ←

Check again that the two boards are parallel, that all the LEDs are the same height. Check the long LED legs are through the pins marked +.

SOLDER!

Once you’re happy, solder one pin on each component - one LED leg, one pin on a pot (not the big legs), one pin on each socket.

I recommend this because it’s easy to reposition or fix a part when only one pin is soldered. If it’s out of place or not flush against the PCB, you can just reheat that joint and snap it into place.

Check again. Once you’re happy everything is aligned, go back to solder all the points.

Side view checking Radio Music panel and PCB alignment — Side view: check the PCB is parallel to the panel.

Second side view checking Radio Music panel and PCB alignment — Second side view before finishing the soldering.

Back of Radio Music PCB after first stage soldering — First stage soldering complete.

6. Add the button and SD card holder ←

Now go back and add the button and SD Card holder. These are the fiddliest parts to mount, so take it slow and steady.

The pushbutton has one flat side. Make sure this side matches the flat side on the PCB artwork. There are two very fine LED pins under the pushbutton, make sure they’re not bent and can go through the holes.

The SD Card has very fine pins. Check none are bent then place it on the board.

Attach the front panel and tape the SD Card Holder and pushbutton into place.

At this stage, the ‘solder one pin first’ rule is particularly important. Solder one of the larger pins on the pushbutton, and one of the larger ‘leg’ pins at each end of the SD Card holder.

Gently remove the tape and check…

The SD Card holder should be flush against the PCB at the bottom, and aligned with the slot in the panel.

The pushbutton should also be flush against the PCB, and it should work smoothly when you tap it, not rubbing against the panel.

Once you’re happy, solder all the pins. The tiny pins on the SD Card holder are very tiny, but the soldermask makes it easier than it looks to solder them cleanly.

Radio Music pushbutton and SD card holder ready to fit — Button and SD card holder.

Radio Music PCB with pushbutton and SD card holder placed — Place the button and SD card holder.

Radio Music panel refitted over button and SD card holder — Refit the panel before soldering.

Radio Music panel with tape holding the button and SD card holder in place — Tape holds the final parts in position.

7. Checking, trimming and finishing ←

Now check your work. If you have one, get a magnifying glass and some bright light to check each of the solder joints on the back. You’re looking for missed joints (I always miss at least one joint, somehow), and blobby joints that don’t look like the OK joints in the picture at the top.

Add any missing joints, reflow any you’re not sure about. You don’t need perfection, just ‘OK’ joints. It’s not normally about adding more solder, although sometimes that is required.

At this point, trim the long legs of the LEDs. This can also reveal a missing joint, or a point to touch up.

Once you’re happy, you can finish the build:

Add the rest of the nuts and tighten them using pliers with tape wrapped round the end, or a fancy tool if you have one.

Push on the knobs. These push straight on. Make sure the knob buttons still click when they’re on.

Add the power cable. You’re done.

Back of Radio Music PCB after final soldering — Final soldering complete.

Back of Radio Music PCB after trimming component legs — Trim the LED legs.

Radio Music front panel with knobs fitted — Fit the knobs.

Radio Music power cable connected to the rear power header — Connect the power cable in the correct orientation.

Testing ←

Once you’re finished, use the Radio Music testing guide to check the controls, sockets, LEDs and SD card playback.