Congratulations! You’re a few simple steps away from owning a great modular synth power supply 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 Dualist power supply, we hope you make great music with it!
Tools
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)
- M3 nut driver, socket, spanner or pliers
You’ll also need a clean, well-lit workspace with a heat-resistant surface to work on.
Build Instructions
Putting our Dualist power supply together is pretty straightforward; the parts count is low, the parts are easy to identify and all of the parts go on one side of the PCB.
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.
Typically 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). We’ll only deviate from this approach occasionally where it’s sensible to do so.
R1 and R2 – 2K4 resistors
We’ll be working entirely on the side of the PCB that has the component markings and references printed on it. Locate the positions for R1 and R2 and solder both of the resistors into place. It doesn’t matter which way round they go as long as they’re in the right location. 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).
D1 to D6 – rectifier diodes
There are six of these 1N4004 diodes located around the PCB. Diodes have to be inserted the correct way round – so make sure that the white bar at one end of the diode matches the bar on the printed symbol. Set each diode into place, check it, then flip the board over and solder it into place.
Repeat until all of the diodes are soldered.
C4, C5, C9, C10 – tantalum bead capacitors
These capacitors are polarised, which means there’s a right way to orient them on the board.
The longer leg of the capacitor goes into the hole marked “+” on the PCB; it can sometimes be a little unclear as to which is the longer leg on these components, so you can also look for the “+” marking n the body of the capacitor.
Locate the positions for these capacitors on the PCB, check that they’re oriented correctly and then solder them into place.
J1 and J2 – 4-pin headers
You’ll find the locations for these in the middle of the left edge of the PCB. Working with one at a time, locate the pin header in the holes, flip the PCB over and solder into place.
You might find it useful to just solder one pin, then check that the header is straight, making any adjustments before soldering the remaining 3 pins.
J4 – box header
This Eurorack power header has to be correctly oriented in order to function properly and not damage your modules, so take great care to ensure that the gap in the header shroud matches the gap in the printed outline on the PCB silkscreen.
Position the header, then flip the board over and solder one pin into place.
Before you continue to solder the remaining pins, flip back over and check once more that the header is correctly oriented.
If you are happy that everything is laid out correctly, continue to solder all of the remaining pins.
U1 and U2 – voltage regulators
The voltage regulators, although they look identical to each other, perform different functions and have different pin assignments so it’s essential that they are correctly placed on the PCB.
We strongly advise that you work with one regulator at a time, and check the print on the component to ensure that you’re working with the correct one (U1 is LM7812, U2 is LM7912).
It’s important that each regulator 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.
Position a heatsink over the printed outline on the PCB, then locate the regulator pins in their holes; you should now be able to pass an M3 machine screw through both the regulator and the heatsink and secure them into place with an M3 locknut on the backl of the PCB.
Double check that the regulator is the right component in the right place before soldering it into place,
Repeat the process for the other regulator.
J3 – 2-way terminal block
JK1 – 2.5mm socket
These components offer options for how you get power into your Dualist. We recommend that you add both so that your Dualist is ready for any future changes in your modular setup.
Both parts should be oriented with the open side facing the edge of the PCB. Locate the pins in their holes and then solder the parts into place.
Important note: on the initial release batch of the PCB, one of the holes for JK1 is tight; you’ll need to either pinch the pin with pliers or file some of it away to reduce its width slightly in order for it to fit. This does not affect the function of the component at all and this detail will be rectified in the next batch of PCBs.
C1, C2, C3, C6, C7, C8 – electrolytic capacitors
These large 4700uF capacitors smooth the regulated power. Electrolytic capacitors are polarised – they have a positive and a negative connection and these have to be the right way round. If you look at the locations for these capacitors on the PCB you’ll see that one hole has a “+” or “+++” 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 stripes are all on the side that faces your 16-pin box header J4. Push the capacitors down snug to the board and solder them into place.
That’s it, your Dualist is ready for testing and use.
Testing
Before we connect Dualist to a power supply, we’ll make a quick test for short-circuits. You’ll need your multi-meter for this step.
With your meter set to detect continuity
Work with the pin header J1. Using your meter, ensure that there is NO continuity between the four pins.
Next, check the 16-pin IDC header J4 and ensure that there is NO continuity between any two pairs of pins.
If your Dualist passes this test, it’s safe to connect it to your power supply and continue with the next set of tests. If it fails this test, take a good look over the back of your PCB for shorts between soldered connections. Rectify and try again.
Powering up
Dualist requires a 12V AC-AC supply with a 2.5mm barrel socket (we chose the 2.5mm component as we found that in this application they seem to “latch” more securely than equivalent 2.1mm connectors). We’ve found some suitable power supplies here (1A) and here (2A, which we recommend), but both are supplied with 2.1mm connectors; if you bought a Dualist kit, you’ll have received a 2.5mm replacement plug as part of the kit, however if you need to obtain one of these they’re available from one of our favourite suppliers.
Important note: Dualist requires a 12V AC power supply; you can’t use a DC power supply with this module or with the Dualist PSU. You must not try to power the Dualist PSU directly from mains voltage!
With your meter set to measure voltage
Connect your 12V AC supply to Dualist via J3 or JK1.
Work with the 4-pin header J1. Touch your meters BLACK probe to pin 3 (GND).
Touch the RED probe to pin 2 (+12V). You should measure approximately 12V here (a small amount of drift is acceptable).
Touch the RED probe to pin 4 (-12V). You should measure approximately -12V here (a small amount of drift is acceptable).
IMPORTANT NOTE: These tests are designed to ensure that Dualist
- is safe to use
- will not damage your power supply
- will not damage your Eurorack modules
Skipping these tests, carrying them out improperly or ignoring the results can carry serious risks and consequences for you and your equipment. In proceeding to connect Dualist to your equipment, you are assuming liability for any consequential loss or damage.
Connecting up to your system
There are lots of options for connecting your modules to Dualist:
- Connect a flying header cable directly to J4
- Connect a bus board via a 16-way cable and J4
- Connect a bus board via a custom cable and J1
- Connect a ThirdRail via J1
- Connect a MiniBus via J1
Bill of Materials
In addition to your PCB you’ll need parts. The full list of parts for the project is given below, with Mouser and BitsBox part numbers to aid you in identifying compatible parts. Although we’ve used all Mouser and BitsBox parts in the example build above, you may be able to obtain cheaper compatible parts by shopping around.
| Reference | Value | Description | Qty | Supplier & Part | Notes |
|---|---|---|---|---|---|
| C1, C2, C3, C6, C7, C8 | 4700uF | Electrolytic capacitor, 25V, 105 deg, 7.5mm pitch | 6 | Bitsbox EC4K7U25 | |
| C4, C5, C9, C10 | 1uF | Tantalum Bead Capacitor, 25V, 5mm pitch | 4 | Bitsbox CT1U035A | |
| D1, D2, D3, D4, D5, D6 | 1N4004 | Rectifier diode | 6 | Bitsbox QD023 | |
| J1, J2 | 4-pin male | IDC header | 2 | Bitsbox CN202 | |
| J3 | 2-way | PCB Mount Terminal Block, 5mm pitch | 1 | Bitsbox CN020 | |
| J4 | 2×8-pin, male | Shrouded IDC header | 1 | Bitsbox CN210 | |
| JK1 | 2.5mm 30V | PCB-Mount DC Power Socket | 1 | Bitsbox CN019 | |
| R1, R2 | 2K4 | Resistor, metal film, 0.25W, 1% | 2 | Mouser 603-MFR-25FRF52-2K4 | |
| U1 | LM7812 | Voltage regulator +12V TO-220 | 1 | Bitsbox QD002 | |
| U2 | LM7912 | Voltage regulator -12V TO-220 | 1 | Bitsbox QD075 | |
| U1, U2 | Heatsink | Drilled fixing hole, 21 deg C/W, 19 x 19 x 9.5mm | 2 | Bitsbox HW090 | |
| 2.5mm 12V | DC Power Plug 1A | 1 | Bitsbox CN016 | ||
| M3 x 6mm | Machine screws | 2 | Use eBay or local hardware store | ||
| M3 | “Nyloc” nuts | 2 | Use eBay or local hardware store |
Make Synths Not War 