Build a Power Supply for Your Guitar Pedals

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Introduction: Build a Power Supply for Your Guitar Pedals

IMPORTANT NOTE:

ELECTRICITY IS DANGEROUS! DO NOT ATTEMPT THIS PROJECT WITHOUT PROPER KNOWLEDGE AND SAFETY EDUCATION REGARDING WORKING WITH MAINS VOLTAGE ELECTRICITY! IT CAN AND WILL KILL YOU! HOMEMADE ELECTRICAL ITEMS USING MAINS POWER SHOULD NOT BE LEFT UNATTENDED DUE TO A POTENTIAL FIRE RISK. FOLLOW THESE INSTRUCTIONS AT YOUR OWN RISK.

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:

https://cdn.instructables.com/ORIG/FZG/YM90/G5703OX4/FZGYM90G5703OX4.jpg

Step 2: Parts and Tools

Parts:



- 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

- Wire

- Solder

- Assorted nuts and bolts

- Small segment of aluminum

- Masking tape

- Electrical tape



Tools:

- Drill and bit set

- 1 1/4" hole saw bit

- Hot glue gun

- Soldering Iron

- X-acto knife

- Wire strippers

- Wire cutters

- Square

- Ruler

- Flat file

- Vernier

- Multimeter

Step 3: Drilling and Cutting

Short version: 



Cover in masking tape, mark hole locations, drill pilot holes, drill appropriate sized holes using pilots as reference.



Long version:



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

Short version: 



Build the circuit, remember to cut the rails on your stripboard to separate segments.



Long version:



 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!





Matt


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1 Questions

can i use 12v wall wart adaptor instead of transformer? just like this.. its rated 12v 2A.. is it ok to use it instead of transformer?

and how will the schematic diagram goes on? does any parts of it will be omitted?

tia

unnamed (1).jpg

Yes that will work, just omit the transformer, bridge rectifier, and reduce the large capacitors from 10kuF to 100uF. Also use 7809 regulators.

321 Comments

Nice project Matt! However, you have attracted a lot of "newbies" to this project which I would have given a Big Red Letters WARNING about using Mains Power! Newbies have too much to learn BEFORE mains should even be attempted! If someone can't read that the group of diodes (power rated!) connected in that funny pattern is a bridge rectifier - they shouldn't be attempting this level of project OR as someone wished: use a wall wart for powering the whole thing. Sorry, you can't give a whole lot of directions AND THEN SAY it's lethal! That could be too late. You only get one chance! And 60 Hertz!

You're right, so I added a bold and capitalized paragraph warning people of the dangers of working with electricity without precautions.

You need a lower voltage secondary capable of more current. 18v bridge rectified will get you 24-25v Dc which will require your regulators to consume excessive wattage and become very hot. Consider a correctly spec’d PT, dropping resistors for the smaller regulators as well at heat sinks.

Also Is the block of Diodes in the diagram the Bridge Rectifier?

I'm trying to make this with only 9 volt output jacks - what components would change in value? I don't want to blow up my pedals but I really like this design. I'm making the list of things to buy to make it. Does the volt rating on the bridge rectifier matter? I'm finding a variety of them. Would 4A 600v work?

Also all the LEDs I'm finding are 12V. In the schematic I see yours is connected to 5V. Can I do the same thing with the 12V side and eliminate the 5V loop altogether? Your list calls for a 220 ohm resistor but what is the Watt value? Would it change with a 12V LED?

Sorry for the Newbie questions, I'm learning as fast as I can. Thank you for this!

would be nice to have given us the veroboard layout picture!

I like this! Would you recommend a higher rating transformer though?

I noticed you are using a 0.3A transformer, is that okay to use with my pedals of each of them needs 0.3A each also. I'm a beginner at this so I had to ask. I currently have a 3A DC adapter where I added more extension plugs that makes it 3 connectors in all. So I'm thnking the 3 pedals with 0.3A rating can be sufficely served with the 3A. So my question is that is this kind of perpective correct or I should be worried? I am hoping that a 0.3A rated multiplug supply can suffice with many 0.3A rated pedals. Would it cause humming or will it work well? Thanks!

I agree, 0.3A is very low. I would not use something so low next time. I haven't had any issues with it though, running several pedals. The thing is, it can deliver more than 300mA, but the voltage at the transformer secondary may drop lower than 18V AC, but there is a lot of voltage headroom in the design.

There's really no chance for an issue until the transformer overheats to the point of failure, which would take some doing.

Hi,
I made a very similar power supply myself, probably some slightly different value for the caps and added a mains filter (salvageable from most appliances, sometimes already attached to a nice socket).

However I did a mistake, that I also see in your schematic, so I am curious to know if you had the same problem as I did, or why didn't you.

The "mistake" is to have a common ground to all the power outputs. Since another another ground is shared between the guitar pedals through the audio signal cable, this creates a "ground loop" and causes a hum. Did you experience this?

In my case it happens with just 1 pedal on the 12V and another pedal on the 9V. On both pedals I know that the signal ground is connected to the chassis and the power ground (as usual on most stompboxes).

Note that I get absolute silence if I mute the guitar and:
- use a single pedal (any of the two)
- power one of the pedals with a different power unit (on the same wall outlet)
- break one of the ground connections (either one of the power grounds, or disconnecting the shielding in the signal cable between the two pedals).

So.. Do you get the same problem? if you don't, do you know why?

The only solution i can think of is to have an individual rectifier and filtering for every output, sharing only the transformer.. but that's not a ideal solution.

Honestly it's been a while since I used this thing. I never had major problems with it but I had a lot of hum anyway, from other sources, and so I can't say for sure what kind of issues my grounding might have been causing.

You're right about breaking the grounds and splitting it up so the cables are shielding but not passing current from one unit to the next.

I think the only way to properly do the isolation is to have individual transformer taps, so the outputs are totally galvanically isolated from each other. I don't think different bridge rectifiers will isolate it properly. The diodes pass current back to the same windings.

If you can find some low cost isolating DC/DC converters you can put them all together powered off the same DC source and their outputs will be fully isolated.

These are about the cheapest 9V output isolated ones on digikey http://www.digikey.ca/product-detail/en/cui-inc/PDS1-S12-S9-S/102-3012-5-ND/4006980