If you're like me, you know how annoying it is to use up 9V batteries on your guitar effect pedals. Its wasteful, and brand name 9V's are almost $9 for a two-pack. If you forget to turn off your pedals you've thrown away big bucks. Its an extreme waste of money when you can build your own power supply for only about $25.The power supply I designed and built delivers steady, regulated 12 volts, 9 volts and 5 volts all at the same time. Each voltage has two outlets, but they can be "daisy chained" with a custom cable to connect many more pedals. The styling is an homage to the old days of vacuum tubes, when components generated so much heat they needed to be on the outside of the casing instead of inside. I used some gigantic capacitors that I thought would look cool, other than that they are major overkill. In this Instructable I am going to assume that you know some basic electronic skills and know what I am talking about when I say capacitor, resistor, LED, transformer, AC and DC, etc. There are lots of introductory electronics Instructables and soldering Instructables you can check out if you'd like to gain a better understanding of basic electronic principles and components.IMPORTANT NOTE: Depending on what pedals you intend to use this for, you should take care to wire the DC connectors as pin-positive/ring-negative or pin-negative/ring-positive. The latter is the industry standard way of doing it, although it poses issues when building a pedal that has a metallic housing. I prefer pin-positive/ring-negative because of that issue, and I wired this supply in this way. Please take care as to which way you wire the power supply to prevent damage to your pedals.
Step 1: Planning and Schematic
The first thing to do is design the circuit. Many guitar pedals and stompboxes have 9V DC power jacks on the back (if your's doesn't and you're feeling ambitious, you can add your own) which we will use to power them instead of the 9V internal battery clip.
The schematic I designed can be modified for whatever voltages you would like. For example, if you don't have any 5V pedals, you can just swap the 5V power regulator for a 9V regulator, and now you'll have double the 9V power.
The schematic uses a simple power supply circuit converting AC to pulsating DC, smoothing it with capacitors and running it through voltage regulators for fixed DC outputs.
Here is a higher resolution version of the schematic if you can't read the one below very easily:
Step 2: Parts and Tools
- 5" long by 2.5" wide by 1.75" tall project box
- Segment of stripboard, veroboard (it's like perfboard but the copper is in strips, see pic)
- 7809 (9v) and/or 7812 (12v) linear voltage regulator(s), depending on the voltages and configuration you want
- 18V Transformer
- Bridge rectifier
- IEC Power connector
- Two 10000uF 50V capacitors (less overkill version: 100uF)
- Three 10uF 63V capacitors
- Toggle switch
- Green LED
- 5mm LED holder
- 220 ohm resistor
- Fuse holder
- 100mA fuse
- Six 2.1mm DC jacks
- Six 2.1mm DC connectors
- Adhesive rubber feet
- Assorted nuts and bolts
- Small segment of aluminum
- Masking tape
- Electrical tape
- Drill and bit set
- 1 1/4" hole saw bit
- Hot glue gun
- Soldering Iron
- X-acto knife
- Wire strippers
- Wire cutters
- Flat file
Step 3: Drilling and Cutting
Cover in masking tape, mark hole locations, drill pilot holes, drill appropriate sized holes using pilots as reference.
I did the layout freehand, marking the middle of the box using the square, and just measuring and sizing up locations using the components. To make it easier to write on the box, cover it in masking tape. Use a sharp pencil so that you can get accurate markings and can erase if you make a mistake. Take your time and get it right, theres no turning back once you start drilling.
Use a 1/8" or 3/32" drill bit to drill pilot holes at each hole marking. For the IEC connector hole, drill in each corner of the rectangle.
After I drilled pilot holes in the corners I used a 1/4" bit to drill around the perimeter of the rectangle, being careful to not pass over the edges. Then, I used some pliers to snap the remaining plastic out of the center, and used the flat file to file it into a rough rectangle. Keep filing and test fitting the connector until it fits snugly. Be careful with IEC connectors that have pop-out flanges to lock them in place, since those are most likely designed for metal enclosures and thick plastic may prevent them from locking in place. I had to switch for a connector that had mounting screws because of this. Once the connector is in place, you can drill holes for screws or bolts/nuts with no problems.
The rest of the holes will need to be drilled appropriate to the bolts you've selected for mounting your transformer and the diameter of your capacitors. My capacitors were 30mm diameter, so a 1 1/4" drill (about 32.5mm) worked great. The diameter of most DC jacks is about 8mm, but check with a vernier before you drill.
The aluminum plate that goes over the DC jacks is 4" long by 1" wide. I used a 5/16" drill bit for the holes on it, spaced 5/8" apart. You can use the bastard file to remove the sharp corners, and some 120 grit sandpaper to smooth the edges and give it a brushed look. I used 4.40 threaded hex head screws to secure it in place.
Step 4: Circuit Building
Build the circuit, remember to cut the rails on your stripboard to separate segments.
Now that the chassis is sorted out, the next phase is wiring up the circuit board. Measure the inside of the project box and determine how much room you can use for the circuitry. I used a piece about 2" by 2.5" and it fit great and was still easy to populate with components.
If you don't get a pre-cut piece of that size, the easiest way to cut it without using power tools is to score the edge to break it at with the x-acto knife, then break it over the edge of a table, holding both sides of the break firmly. You may need to break off more than you want with the first break.
To cut the traces on a stripboard, you can use a drill bit held in your hand and just turned into one of the holes until the metal is scraped away and broken. A close-up picture below shows the result.
I didn't have a plan going into this, but I basically just set up + and - rails and lined up the regulators on them. The regulators all use the input voltage from the transformer (18V AC ends up being around 28V DC) and common grounds, so they can be placed in a line, and then the output pin connections can be cut with the drill bit.
I wired the large capacitors off-board because I wanted them to protrude from the top of the chassis, and they just take up too much room on the PCB.
Solder the 220 ohm resistor to the LED. Then solder wires to the resistor and LED and connect the positive wire of the LED (the longer leg) to the output of the 5V regulator and the negative wire to any negative point on the board.
Testing the circuit is difficult, so just triple-check that everything is correct. Before you turn it on use a multimeter to check for shorts between ground and the input voltage, and check each output voltage with the input voltage and ground to make sure nothing is shorted out and would cause damage.
Step 5: Assembly
Short version: Put it together.
Long version: The best components to start with are the DC jacks. I used hot glue to hold them in place because the threaded portions weren't long enough to reach through the plastic and the aluminum and still have room for a nut. Make sure that they are all aligned straight ( I messed this up) so that they will be easier to wire up. Use lots of hot glue to make sure they won't get pushed in when being plugged into.
Next, install the transformer, fuse holder and IEC receptacle. Use nuts and bolts for the IEC and the transformer, and use the nut supplied with the fuse holder to fasten it in place. Also put the toggle switch in place so that you can wire up the AC portion of the circuit before the big caps and board get in the way.
That being said, now is a good time to wire up some more of the circuit. Solder one wire from the primary (120V) side of the transformer to one of the locations on the back of the IEC receptacle. The two that are next to each other are the Live and Neutral, the other lower one is the Earth which we won't use since this is a plastic housing. Connect the other wire from the primary side of the transformer to the fuse holder, then solder a wire from the fuse holder to the toggle switch, and from the toggle switch back to the remaining connection on the IEC receptacle. The chain should be:
IEC -> Transformer -> Fuse -> Toggle switch -> Back to IEC
Now that those are in place, put in the circuit board and caps. To affix the capacitors, I put a zip tie around each one, and then rested them inside on the zip tie, and glued them in place.
Step 6: Assembly Continued
Solder the wires from the secondary side of the transformer to the AC input pins of the rectifier on the circuit board.
To hook up the DC jacks, cut nine pieces of wire about 1" long. Solder wires from the center pin of Jack 1 to the center of Jack 2, Jack 3 to Jack 4, and Jack 5 to Jack 6. With the remaining 1" segments, daisy chain wire to a remaining pin on each jack. This will link all the negatives together.
Cut four 3" segments of wire. Solder one end of each to the 12V regulator output, 9V regulator output, 5V regulator output, and a common negative point, respectfully. Then solder the other ends to a center pin of a 12V jack, a 9V jack, a 5V jack, and the daisy-chained jack negatives, respectfully.
Put the LED holder in place, and snap the LED in.
With the board up away from the jacks, make sure there are no short circuits, especially on the AC side of the circuit, and then carefully plug in the power supply and see if it works. Use a multimeter to check that there is 12V at the 12V jacks, 9V at the 9V, etc. The LED should light up.
BE EXTREMELY CAREFUL AS YOU HAVE LIVE EXPOSED 120V WIRES THAT COULD ELECTROCUTE YOU VERY EASILY.
Next, put some electrical tape across the DC jacks so that nothing on the circuit board can touch them and short out. The metal plates on the regulators are connected to ground and will short out anything they touch. Also tape the pins of the capacitors and around the 120VAC connections for safety.
If everything works great, bend the circuit board back into the case. A nice touch would be to put some two sided tape on the back of it and stick it to the inside of the cover plate. Screw the box shut.
Step 7: Finished!
You now have your very own guitar pedal power supply! Use it to run your pedals without having to waste batteries and streamline your pedal board or setup without needing several DC wall adaptors.
The beauty of this design is it is very customizable and expandable. If you include a center-tapped transformer you can add negative voltages to power some elaborate homebrew pedals or amplifiers. The possibilities are endless and this is a great starting point.
I hope you liked my Instructions. They're a little long in the tooth but I wanted to make sure that the maximum amount of information was available with minimal misinterpretation. Please leave a comment if you have any questions or thoughts.
Thanks for reading!