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.  

<p>This works fine. I added a LM317 circuit for variable DC as well and a small fan in there. The fan adds some noise though so it will have to go. </p><p>Thx for sharing!</p>
<p>Nice work. Glad it was helpful for you. If you can make room for a bigger fan, that would help make it quieter.</p>
<p>I like this! Would you recommend a higher rating transformer though?</p><p> 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!</p>
<p>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.</p><p>There's really no chance for an issue until the transformer overheats to the point of failure, which would take some doing.</p>
<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 this!</p>
<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>Is there noticeable difference if i use a transformer with any miliamps?</p>
Can you explain more?
<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?
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>

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