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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:

http://img.photobucket.com/albums/v321/mattthegamer463/Schematic.png

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<p>Hi, <br>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).</p><p>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.</p><p>The &quot;mistake&quot; 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 &quot;ground loop&quot; and causes a hum. Did you experience this?</p><p>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).</p><p>Note that I get absolute silence if I mute the guitar and:<br>- use a single pedal (any of the two)<br>- power one of the pedals with a different power unit (on the same wall outlet)<br>- break one of the ground connections (either one of the power grounds, or disconnecting the shielding in the signal cable between the two pedals).</p><p>So.. Do you get the same problem? if you don't, do you know why?</p><p>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.</p>
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. <br><br>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. <br><br>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.<br><br>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. <br><br>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
<p>Thanks for your reply! </p><p>In other forums meanwhile I also learned that multiple rectifiers wont solve it.</p><p>Multiple small transformers or one transformer with multiple taps seems to be the general agreement to solve that.</p><p>Your suggestion to use DC/DC converter is very interesting, I didn't know that such thing existed. Definitely cheaper than buying transformers! </p><p>But (just for the sake of healthy discussion) I'm not sure if I like it .. I'm pretty sure that, inside, those things are basically mini switching power supplies.. aren't those noisy by nature? it kills the whole purpose of starting with a real transformer. Even if it doesn't add any noise, it kills the old-school-ness of this simple circuit, with some magic over complicated component.</p><p>I didn't have the time to do the proper testing, but what I am thinking now is to add a decoupling inductor between the grounds of the regulating stages. I don't see why it wouldn't work, although i have no idea which size to use. (also because I have some recycled inductors around). What do you think of that?</p>
<p>Those DC/DC converters operate around 100kHz, so any self-generated noise on their output is well out of the audible range.</p><p>Inductors might help, but I don't know. Probably would help. Ideally, eliminating ground loop paths and forcing all ground current to return in a star-pattern. Modifying some cables might be required.</p>
<p>I will consider that!</p><p>thanks!</p>
<p>Hi, Thank you for sharing this project.</p><p>I just wanna ask if I can remove the IEC receptacle.connector and directly connect it to a wire with a 2-prong plug. I think it would be okay but i asked just to make sure. Thanks!</p>
That's fine, it will work. I would recommend you use a 3 prong cable and put the ground wire to any external metal components, for safety.
<p>Is there any alternative to the bridge rectifier you used? I can't seem to find that particular type. Thanks man!</p>
any bridge rectifier with a current rating of a few amps or more will work. you can also make a diode bridge using 4 silicon diodes.
<p>Will it matter if I use a 500mA fuse?</p>
<p>500mA fuse on the 115V side is fine. It just needs to protect the wiring from the outlet to the power supply.</p>
<p>Is it normal that I'm getting so much heat from the voltage regulators? I had to squeeze in a small heatsink, but it doesn't seem to help at all. Any idea on how this can be fixed? Thanks dude</p>
<p>What is the input voltage to the regulators? Do they get hot with no pedals connected? If they get hot without pedals then there is a circuit problem.</p><p>Linear regulators are very inefficient, at 1 amp output they have to dissipate 1 watt for every volt dropped across the input to the output. </p>
<p>They don't get hot when there's no load. I use an 18v transformer and I'm only using 9v outputs so I think I should lower the transformer voltage since I do get more when it passes the rectifier. Should I get a transformer lower than 9v then?</p>
<p>You could try switching to a half wave rectifier, which would help to get rid of some excess voltage. </p><p> <a href="http://www.circuitstoday.com/wp-content/uploads/2009/08/half_wave_rectifier_with_capacitor_filter.jpg">http://www.circuitstoday.com/wp-content/uploads/20...</a></p>
<p>Oh, one more thing, up to how many output jacks can I connect off of a single regulator?</p>
You can connect as many as you want, but your pedal current draw is limited. A properly heatsinked 78XX regulator can deliver 1A so you could run ten 100mA pedals or only one or two high current pedals. The sum of the currents can't exceed 1A
<p>Anything wrong with this circuit? I haven't connected the transformer yet and I only plan to have 9v output. I appreciate your help dude, I'm quite new to electronics.</p>
<p>Looks good to me.</p>
<p>Looks good to me.</p>
<p>Thanks dude!</p>
<p>Looks Great! This is exactly what I was looking for. With a little modification I can use this as the basis for a custom pedalboard power supply. Thanks!</p>
Hi, great design u for there!<br>Just wondering, are u able to make a power adapter to supply a 9v, 12v and 15v pedal all at the same time?
Yes, it can be done by designing the output of the rectified transformer output to be higher than 15V DC, then using 7815, 7812 and 7809 linear regulators to get the three voltages.
<p>thanks matt! i dont know if its too much to ask, but is it possible to make one for me? i'll pay for the parts, service and shipping :)</p>
<p>I'd recommend something like an MXR iso-brick, you'd bet better value for your money than paying me to make you one.</p><p>http://www.musiciansfriend.com/accessories/mxr-m238-iso-brick-power-supply-unit</p>
<p>Hi there, great design and something I've been looking for a very long time.</p><p> I have a question? I need a power supply at 9VAC / 2.1A for an old digitech GNX3. I can find wall warts for 9VAC / 1A but nothing closer and anyway they are way too exspensive here in Australia. Do you have a design along the lines I need that I could use? <br><br>I loved this old GNX3 but burnt through way too many PS's [12 monthly] and it's been sitting idle for the past 7 years. Any help appreciated.</p>
If it's an unregulated AC wall adapter that's needed, all that is really is a trasnformer that outputs 9V AC at 2.1A of load. A transformer like this is pretty close to what you'd need:<br>http://www.digikey.ca/product-detail/en/triad-magnetics/VPT18-1390/237-1323-ND/2090061<br><br>There are not a lot of cheap options as AC wall adapters are more costly produce now than cheap chinese-made DC wall adapters.
Some pedals are more power hungry than others. (Boss 55mA, Strymon 650mA, etc). When building a power supply, how can we ensure or produce a circuit that will handle the current draw of a desired pedal? How would I build one of here and purpose one of the outputs to handle a 650 mA draw?
The key to supplying enough current from a linear regulator is to be able to cool it well enough. The 78XX series in a TO-220 package can deliver 1A of current with proper cooling, so if you add a heatsink they can deliver 650mA pretty easily. The waste energy in watts is (Vin - Vout) * output current. If it is high you'll need a heatsink, if it is low (say 0.5W) maybe you can avoid a heatsink. Heatsinks are easy enough to include regardless. The 78XX series has a 75deg C automatic shutdown feature which will prevent them from burning out too easily so you can try it and see if it works and add additional cooling if needed.
Thanks for the info. That helps lot!
Hey I can use a 12 volts secondary if I'm only using the 9v ic right?
Yes
Thank you kindly
<p>Amperage output of the transformer doesn't matter too much does it? I have a few 12V 4A transformers sitting around I'd like to use and I didn't notice a maximum amperage on the 78XX spec sheet. Each VR would receive 1.3A in this instance with a regulated output of 0.5A to 1A, each power socket would receive 250mA to 500mA if I'm not mistaken. Some of my Boss pedals specifically require no more than 200mA. Connecting an additional one or two power sockets to each VR could mitigate any issue there but only so long as an actual pedal is connected to each socket and drawing power, thus divvying up the current equally. Any thoughts on this?</p>
Circuits only draw as much current as they want. Difficulty is, ohm's law dictates that the higher the voltage across a fixed load, the more current it will consume. 2x the voltage = 2x the current = 4x the power = poof of smoke.<br><br>If your boss pedals want 200mA, they'll only take as much as they want.<br><br>Your 4A transformers can deliver 12V and 4A, they might run a little higher voltage with a light load on them, but they will work. The max amperage of 78XXs is pegged to the case type. The TO-3 package can handle up to 1.5A with a heatsink, I think, however, the true limit is linked to the difference between voltage in and voltage out, the amount of current being drawn, and the thermal coefficient of the junction to case, case to heatsink, and heatsink to air.<br><br>In short, you won't draw more current than you need, as long as your voltage is regulated and correct. It doesn't matter if the supply can deliver 100mA or 100A.
<p>Hey Matt ! </p><p>Good project ! and excellent explanations . You stressed the importance of the voltage rating of the capacitors , another thing that a novice might miss , would be the polarity of a capacitor , hook it up backwards , and it will smoke ! A little humor here :</p><p>All electrical devices operate on the captive smoke inside it . When the smoke gets out ,the device quits working !!</p><p> One analogy that may help folks to understand what you said about things just drawing the current that they need , would be a car 12V ( actually about 13.8V , but close enough ) electrical system . The battery can give the starter motor hundreds of amps , but the radio , headlights etc , only draw the current they need to operate . As far as transformers go , It pretty much has to do with the turns ratio ,( the primary voltage vs secondary voltage ) , and is normally rated as an RMS value . When you rectify the AC voltage and feed a filter capacitor , the capacitor ( under no load or very light load ) will charge up to the &quot; peak &quot; voltage value , around 1.4 times the RMS voltage , less the voltage drop across the rectifiers . This kind of explains the need for using a regulator circuit to keep the voltage constant . There are all sorts of modifications that could be done to this circuit , the sky is the limit ! One thing that could be done would be to use a separate regulator and capacitor for each output ( they are cheap , 78xx regulators can be bought for about $1 US each or less ) This could help if you find you are getting &quot; crosstalk &quot; noise between pedals . A beefier transformer certainly wouldn't hurt anything either .</p><p>Cheers , take care , and have a good day !!....73</p>
<p>Thanks. I agree there's room to grow with this design.</p>
<p>Great Instructable! Thanks. Do you see any reason why I couldn't take a computer power supply and regulate the DC voltage down to 9VDC? I have an old laptop power supply that is 20VDC. What are your thoughts?</p>
No that should work. Some laptop supplies may not be a very clean power source, though. Might end up with some audible hum.
Ok. That was my only worry. Maybe it's not worth it then. Where did you get your transformer? Seems like they are $30-$40 in mouser. Or a part number would be awesome. Thanks for the help.
<p>You'd be best off finding a transformer somewhere and using that. The old heavy wall-warts have a transformer in them, which you could use. Something from 9 to 15V output would work with a 7809 linear regulator. The higher the input voltage the more wasted energy and the more heat the 7809 will generate, but that's okay if you have a heatsink. The 78XX series is good up to 35V if I recall correctly, so the only issue is heat dissipation. They have integrated thermal protection that shuts them down at 75C so they won't normally damage themselves too quickly. Also they're pretty cheap so buy a couple extras and if you blow up a couple while figuring out how much cooling you need its not a big deal.</p>
<p>is this an isolated power supply or is that a whole different game?</p>
Totally different game. Isolated outputs require each output to have an isolating DC/DC converter (expensive) or a specialized transformer with many isolated output secondary windings (very expensive). With properly grounded cables, using an unisolated power supply shouldn't be a problem. Most retail units are not fully isolated either.
<p>Hi Matt, I was wondering what made you choose the DC/DC converter that you did as I'd be interested to find the 6V and 12V converters as well? Also, as the min input voltage on the converters is 10.8, does that mean the circuit needs different regulators to feed the higher input requirement of the converters? Or, do the converters replace the regulators?</p><p>Thanks for the help!</p>
<p>The DC/DC converters replace the regulators, they basically just regulate the voltage but in a more efficient way. Some also feature isolated outputs. The unregulated DC from the rectifier and capacitors just needs to be within the module's input range.</p><p>If you're interested in the isolated power aspects, you can also use the converters and just hook them to an off the shelf DC power supply. One like the one below will give isolated 9V from 5V DC from a wall adapter.</p><p><a href="http://www.digikey.ca/product-detail/en/PDS1-S5-S9-D/102-3024-5-ND/4006992" rel="nofollow">http://www.digikey.ca/product-detail/en/PDS1-S5-S9...</a></p>
<p>Awesome project!!! and very clear directions<br></p><p>I am trying <br>to make a mod based on your design. In sum, the project is an attempt <br>to replace a mess of wall warts(photo1). It REQUIRES isolation, as I have many <br>different synths/effects that all run through loopers(photo2/3), so any extra <br>noise compounds really quick. Many use different volts/amps, so it is <br>unlike a standard guitar pedal board that uses uniform-ish pedals. The <br>outputs needed are:</p><p>(4) 4.5V, 1A, pin positive (kaossilators)<br>(2) 9V, 1.7A, pin positive(kaoss pro, korg wave mini)<br>(1) 9V, 1A, pin negative (boss rc-50)<br>(1) 9V, 300ma, pin positive (roland midi splitter)<br></p><p>(1) 12V, 400ma, pin negative (TC helicon)<br></p><p>(1) 12V, 700ma, pin positive <br></p><p>From my limited understanding, I feel it is easiest to use a computer CPU (or similar) and run a DC/DC converter (<a href="http://www.digikey.ca/product-detail/en/PDS1-S5-S9-D/102-3024-5-ND/4006992" rel="nofollow">PDS1-S5-S9-D</a><br> or similar) off the 12v or 5v rails, using one converter for each <br>desired output. This would be done in parallel (correct?). I would <br>prefer to run ALL off the 12 volt rail, because at some point I would <br>like to power this off a portable car battery(and make the whole unit <br>portable). If possible, I would also like to fit all the components onto the board <br>that the synths are mounted to (photo 4/5). I plan to leave the CPU<br> on the ground to reduce EMI noise. Ideally, one cable will connect from CPU to the board, which will have all the circuitry to step down power, reducing the number of plugs I have to undo/redo every time I take this setup out for gigs</p><p>I am only unsure if this <br>will yield the proper results, be safe for my components, and not tax <br>the power supply(or find one that is well equipped to run all this). Also fuses will be required. Any insight you can <br>provide here? </p><p>Again, <strong>the focus is</strong>: power isolation, EMI reduction and <br>portability/form factor. Cost and time are not factors, unless we are <br>talking on infinite scales :)</p>
<p>also, how does one achieve the isolation effect of these converters for outputs that need 12 volts (and thus don't need to be stepped down)?</p><p>Bonus: I also have a behringer mixer that has a (2x 18.5v, 350ma) wall wort I would like to replace. But that is a less straight forward job of soldering the connector. </p>
<p>Well that is quite a complex set of requirements. You may have a hard time finding DC/DC converters which give you enough current to run some of these units. Many of the DC/DC converters that are low cost only output 50-100mA.</p><p>The easiest way to do this would be to build a bunch of isolated power supply circuits using dual-secondary transformers and linear regulators, then you can select each regulator based on the device it has to supply, and you won't have any current issues. The transformers you would need could be found pretty cheaply on eBay, and you could buy a bunch of the same ones and just multiply the circuit as many times as needed. Here is an example of the circuit giving two isolated 9V outputs.</p><p><a href="http://s8.postimg.org/d6b5nro0l/shuper_fuente_scheme_2.png">http://s8.postimg.org/d6b5nro0l/shuper_fuente_sche...</a></p><p>Multiply as needed, power them all from the same 115V supply. For portability, build in or connect one of those 12V to 115V car cigarette lighter inverters, easy to hook to a car battery with no hassle.</p><p>This transformer would give you two 4.5V 1A outputs for kaossilators <a href="http://www.digikey.ca/product-detail/en/VPP10-1000/237-1053-ND/242497">http://www.digikey.ca/product-detail/en/VPP10-1000...</a></p><p>This would give you two 12V 100mA outputs for 12V pedals, you could use the same one for the 9V pedals as well <a href="http://www.digikey.ca/product-detail/en/VPP24-100/237-1064-ND/242508">http://www.digikey.ca/product-detail/en/VPP24-100/...</a></p><p>This would give you two 18V 500mA to run your 18V mixer <a href="http://www.digikey.ca/product-detail/en/VPP36-560/237-1073-ND/242517">http://www.digikey.ca/product-detail/en/VPP36-560/...</a></p><p>So with each transformer you use a bridge rectifier for each secondary winding, and the appropriate regulator to supply each pedal you want to run. The rest is just wiring. You can fuse each output to make sure your pedals are protected if you'd like.</p><p>Obviously this is a pretty involved solution, but I don't see any other elegant way of doing it, aside from just taking those wall warts and zip tying them to a power bar, and putting that in a box with all the cables coming out a single hole. The plan I've proposed is electrically quite similar to whats going on inside all of those wall warts anyway, just extracted and condensed into a single giant power supply circuit.</p>
One of these per output could be used to make a isolated supply. Cost could probably be about $20 + extra $6 per output.<br><br>http://www.digikey.ca/product-detail/en/PDS1-S12-S9-S/102-3012-5-ND/4006980

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