ThruBox Build Instructions

Congratulations! You’re a few simple steps away from owning a great little music-tech gadget that will serve you for years and that you’ll have the satisfaction of having built yourself.

Building this project takes about an hour if you’ve done some DIY electronics before, complete beginners should expect to take a little longer. The instructions assume that you can identify components, solder and do simple voltage and continuity tests with a multi-meter. There are lots of resources available to help you learn these skills – just hit Google or YouTube and you’ll soon be ready to start!

But before you do… we highly recommend that you

  • Take the time to read through this guide a couple of times
  • Check your parts against the Bill of Materials at the bottom of this page to ensure that you have everything that you need

Enjoy building your ThruBox, we hope you make great music with it!


To complete this build you will need

  • Soldering iron
  • Solder
  • Wire cutters
  • A voltmeter or multimeter
  • 2mm allen key (all of our machine screws are hex-headed; you might need a screwdriver instead if you’re obtaining your own hardware)
  • Spanners, sockets or pliers for tightening M3 nuts

You’ll also need a clean, well-lit workspace with a heat-resistant surface to work on.

Build Options

Be clear about which version of the project you are building! These instructions cover both versions.

IMG_7166_thumbThe CASED version – this version of the ThruBox requires both a PCB and a panel and is designed to fit perfectly inside a Hammond 1590B die-cast aluminium enclosure

IMG_7192_thumbThe EMBEDDED version – this version of the ThruBox requires just the PCB; you’ll need to supply your own MIDI and power connectors, terminated to IDC sockets and you’ll also need to devise your own method of securing the PCB inside your enclosure of choice.

Build Instructions, Step 1 – for both options

All components go on one side of the PCB – the side with the part numbers printed on it.

Solder parts into the marked positions; where a part has to go a specific way round there will be markings on the PCB to guide you, and a clear note in the instructions.

We add parts to the board in height order, starting with the shortest parts (this makes the PCB easier to manage and handle during the build).

D3 – small signal diode

IMG_7131_thumbFind D3 in the upper-right of the PCB. Diodes have to be inserted the correct way round – so make sure that the black bar at one end of the diode matches the bar on the printed symbol. Set the diode into place, check it, then flip the board over and solder it into place. You can tidy the wires now with a pair of cutters or do them later (I tend to do mine as I go along as it makes the PCB easier to photograph).

R1 – 10K resistor

IMG_7132_thumbNext, locate R1 – it’s just to the left of the diode you just soldered. Resistors don’t care which way round you put them but you do have to be sure you’re using the correct value – either check it with a multi-meter or refer to this chart to be sure you have the correct resistor. Then put it in place, flip the board over, solder it, tidy if you want to.

R2 to R12 – 220R resistors

IMG_7135_thumbAll of the remaining resistors on the board are 220 Ohms; go ahead and put them all in place. You can give yourself extra art points for keeping the colour bands running the same way right across the PCB (but it doesn’t make any difference to the circuit if you don’t do this, so don’t sweat it).

D1 and D2 – rectifier diodes

IMG_7137_thumbAgain, these diodes have to be inserted the right way around – make sure that the black bar at one end of the diode matches the bar on the printed symbol. Check them again before you solder. These might be a little trickier to solder than the components that you’ve done so far as they soak up quite a lot more heat; if you have an adjustable soldering iron, it’s worth giving yourself an extra few degrees for this part of the job. Wait until these have properly cooled, then, if you’ve not tidied the spare wire away from the back of your PCB yet, do it now – it makes getting at the next couple of components a lot easier.

U2 and U3 – IC sockets

IMG_7141_thumbWe don’t solder Integrated Circuits (“chips”) directly to the board – the heat would damage them. Instead, we use these IC sockets. Although these don’t really have a “correct” way round, it’s sensible to line up the notch at one end of the component with the notch marked on the PCB silkscreen, as this helps us make sure we put the ICs in the right way later.

Holding these in place whilst turning the PCB over can be tricky – I usually locate the socket in the PCB, put a piece of card over it, then turn the PCB and card over at the same time – this holds the socket in place. Slip the card out from under before you start soldering, though.

Install one at a time and make sure that you don’t miss any pins when soldering.

U1 – voltage regulator

IMG_7142_thumbThis component takes the incoming voltage of 9 to 12 volts DC and brings it down to a nice, steady 5V. It’s important that it goes in the right way round, but if you take a close look at the photo you’ll see there’s only one way it will actually fit. First thing you’ll need to do, though, is make it bend at the knees.

Hold the component so that the flat, metal “back” is away from you, the black resin “front” facing you. The components legs are wider at the top – about a millimetre below where the wide part of the leg ends, bend the leg 90 degrees away from you. Do this for all three legs – you can use pliers or even just the straight edge of a ruler to do this. You should now find that the legs fit straight into the holes in the PCB and the flat “back” of the component sits flush on the exposed area on the PCB – the holes in the component and PCB should line up, too.

Although it’s not essential to bolt the component to the board, it’s worth doing – if only to help keep it still during soldering. Use an M3 machine screw and nut if you choose to do this.

C2, C3 and C4 – ceramic capacitors

IMG_7143_thumbAfter that last step, this bit is really easy. We only use one value of ceramic capacitor in this project and they can go any way round, so locate C2, C3 and C4 and get them soldered into place.

C1 – electrolytic capacitor

IMG_7145_thumbElectrolytic capacitors are polarised – they have a positive and a negative connection and these have to be the right way round. Find C1 on the PCB – you’ll see that one hole has a “+” symbol next to it. This shows that the positive pole of the capacitor should connect here – the other hole is, therefore the negative.

There are two ways to tell which connection is which on an electrolytic capacitor:

The positive lead will be longer than the negative lead

The negative lead will be marked by a white stripe down the side of the body (or “can”) of the capacitor

So, put the long leg of the component into the hole marked “+” – this should mean that the white stripe on the body is on the side that faces your 14-pin IC holder for U2. Push it down snug to the board and solder it into place.

That’s the majority of the components in place – but pay close attention because the instructions diverge a bit now, depending on which option you’re building. If you’re making the cased version of the ThruBox, you can skip ahead to step 3, otherwise carry on with step 2.

Step 2 – embedded option only

This part is for the embedded version of this project only – if you’re building the complete, cased version you can skip to the next step.

J1 to J7 – pin headers

IMG_7192Since you’re going to be embedding your PCB inside another project, a rack case or a custom enclosure, all you’ve got left to do is give it a means of getting connected. Solder a 2-pin header to each of the marked points and you’re done!

You can skip ahead to the power test step now.

Step 3 – cased option only

You’ll need the top panel for this step, so make sure you have it to hand; it’s time to add some power to the PCB.

JK1 – DC inlet


JK1 will only fit one way – note how the pin arrangement is “keyed”. Don’t be tempted to solder it into place immediately, though – we have to ensure it aligns with the top panel correctly before we solder it. The first thing we need to do, therefore, is put the mounting posts in place so that our top panel has something to attach to.

Attach a post into each of the four M3 holes and secure it in place with a nyloc-style nut. Make sure they’re nice and snug but don’t overtighten – you don’t want to crush the PCB.

Now put JK1 in place but, again, don’t solder it yet. Instead fit your top panel in place, using M3 machine screws to locate it onto the tops of the posts. Don’t tighten the screws up beyond finger-tight as you’ll need to remove the panel again in a minute.

IMG_7150_thumbEnsure that the DC inlet hole in the panel and the hole in the component align nicely; jiggle JK1 around a bit if you need to. Plugging in a DC plug can be useful here, too – but make sure it’s not connected to mains!

When you’re sure you’ve got it aligned, flip the whole thing over and solder JK1 in place. The holes for the pins are pretty big so be generous with the solder, remembering to heat the pin, the pad and the solder all at the same time to ensure a good connection.

When that’s done and cooled, remove the top panel again and set it aside.

Step 4 – power test

Before we go any further, we’ll just carry out a couple of simple tests to make sure the circuit is going to carry power in the way that we want. We’ll do this before we insert our sensitive ICs into their holders.

With your meter set to detect continuity

Touch one of your meters probes to pin 7 of the U2 socket; touch the other to pin 14. There should be NO continuity between these pins (if there is, take a good look over the back of your PCB and look for shorts between soldered connections. Rectify and try again)

With your meter set to measure voltage

IMG_7212_thumbConnect your ThruBox to a power supply, ensuring that the connection polarity is the right way round and your meter will detect and display 5 volts DC.

Touch your meters BLACK probe to pin 7 of the U2 socket; touch the RED probe to pin 14. Your meter should display 5V (or thereabouts; a small variation is acceptable)

Touch your meters BLACK probe to pin 5 of the U3 socket; touch the RED probe to pin 8. Again, your meter should display approximately 5V.

Assuming all is well, disconnect the DC power – it’s time to carry on. If you’re building the embedded version of the ThruBox, skip ahead to step 6 now.

Step 5 – cased option only


It’s time to add the MIDI connectors. To do this neatly, we’ll need the top panel in place so go ahead and put it back on, remembering to only go finger-tight with the machine screws.

Gently drop JK2 into place (you might need to give it a bit of a jiggle or manipulate the pins a little to get it to seat properly). When it’s in place, you should find that the metal rim of the jack sits less than a millimetre proud of the top panel.

IMG_7155_thumbWe need to flip this over and keep it in place and keep it pushed right into the PCB – we’ve found that using a small coin (a UK penny is perfect) as a “shim” under the flipped-over jack is perfect. Solder one or two pins and then flip it back and check it’s still where you want it to be. De-solder and adjust if necessary, then flip back over and solder the rest of the pins.

Repeat the above for all of the remaining MIDI jacks. When you’re done, you can remove the lid again.

Step 6 – for both options

Insert the ICs U2 and U3 into their sockets. These have to be properly aligned – this is where making sure the sockets were installed correctly pays off.

IMG_7156_thumbRotate the board so that, as you look at it, the notches in the U2 and U3 sockets are at 12 o’clock. In this orientation, pin 1 is at the top left of each socket.

The U2 IC will have a notch in one end. Match this to the notch in the socket, then gently but firmly insert the IC into place. Note that you might need to narrow the splay of the legs a little with some gentle finger pressure first.

The U3 IC will have a solid printed dot in the corner that holds pin 1. Align this with the top left corner of the socket, then gently but firmly insert the IC into place. Again, you might need to adjust the legs of the IC a little first.

IMG_7208_thumbIf you’re making the cased ThruBox, put the top panel back on. This time you can fully tighten the machine screws. If you have an enclosure to put your finished piece into, move on to step 7. If you don’t – that’s fine, you can move on to testing and using your ThruBox.

If you’re making the embedded ThruBox – you’re pretty much done! Connect your preferred power supply and MIDI connectors to the appropriate pin headers and move on to testing and using your ThruBox.

Step 7 – cased option only

IMG_7159_thumbIf you’ve bought our recommended enclosure, now is the time to use it! Unpack it and set aside the lid and the screws (you won’t need them – put them in your “bits box”, they’re bound to come in handy for something, one day!)

If you’ve bought self-adhesive feet, fix one in each corner of your enclosure and give them a good press into position. Now turn the box over and place the finished ThruBox assembly into position. Use the four machine screws that came with your panel to secure the whole thing in place.

You’re finished! Looks great, doesn’t it?


IMG_7210_thumbPower up your finished ThruBox, connect the MIDI OUT from a MIDI source (such as a keyboard) to the IN connector. Then connect one of the five outputs of the ThruBox to the MIDI IN of a synthesizer, sound module or drum machine. Any MIDI messages that you generate from your source device will be passed along to the output device.

If there are any problems at this stage, go back to your PCB and check for shorts, also ensure that the ICs are correctly oriented.

Bill of Materials

In addition to your PCB (and panel if you’ve bought one), you’ll need parts. The full list of parts for the project is given below, with Mouser part numbers to aid you in identifying compatible parts. Although we’ve used all Mouser parts in the example build above, you may be able to obtain cheaper compatible parts by shopping around.

Reference Value Description Qty Mouser Part Notes
C1 47uF Electrolytic capacitor, 25V, 20% 1 80-ESH476M025AC3AA
C2, C3, C4 0.1uF Multilayer Ceramic Capacitor, 50V 3 81-RDEF51H104Z0K1H3B
D1, D2 1N4004 Rectifier diode 2 621-1N4004
D3 1N4148 Small signal diode 1 512-1N4148
J1, J2, J3, J4, J5, J6, J7 2-pin, male IDC header 7 538-87891-0206 Optional – use for EMBEDDED build
JK1 AC/DC 12V Power socket, PCB mount 1 490-PJ-044B Optional – use for CASED build
JK2, JK3, JK4, JK5, JK6, JK7 5-pin, female DIN socket, PCB mount 6 490-SD-50BV Optional – use for CASED build
R1 10K Metal film resistor, 0.25W, 1% 1 603-MFR-25FTE52-10K
R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12 220R Metal film resistor, 0.25W, 1% 11 603-MFR-25FTE52-220R
U1 L7805 Voltage regulator TO-220 1 511-L7805CV
U2 74HC14N Hex Schmitt Trigger 1 595-SN74HC14N
U2 DIP14 14-pin IC socket 1 575-199314
U3 6N137 Opto-isolator 1 859-6N137
U3 DIP8 8-pin IC socket 1 575-199308
M3, 14mm Standoffs 4 855-R30-3001402 Optional – use for CASED build
1590B Hammond die-cast aluminium box 1 546-1590B-BK Optional – use for CASED build
M3 x 6mm Machine screws 5 Optional – use for CASED build; use eBay or local hardware store
M3 “Nyloc” nuts 5 Optional – use for CASED build; use eBay or local hardware store
6-32 UNC x 5/8″ Machine screws 4 Included with our panels
8mm dia Feet 4 Optional – use for CASED build; we like these self-adhesive feet from