DIY SYNTH PSU: How to design a simple dual power supply

[@PWMaarten]

Great video, as usual! One thing people might want to consider building this, the Tab of the 7812 (the part that you screw to the heat sink) is connected to the ground pin. On the 7912 it is connected to the input pin. I wish I could say I didn’t learn this the hard (read hot) way..

[@MoritzKlein0]

yes definitely! forgot to mention this. thanks for pointing it out!

[@dreamyrhodes]

What did you do? Simply isolate the heat sink from the 7912?

[@PWMaarten]

Supertyp there are some special parts available for isolating the heatsink from the tab of the regulator, but these also prevent some conducting of heat. Most of the time I don’t connect the heatsink of the negative regulator to anything on the PCB, if it is mounted there.

[@slother93]

Hi, I’m a mechanical engineer working in the power electronics field and have a suggestion on how to electrically isolate the device from the heat sink while minimizing the thermal impact. The best way I have found is to use Kapton tape (polyimide film) which is an electrical insulator with a very high temperature rating. As long as a single tape layer is used the temperature increase will be negligible. I’d lay down a single strip of Kapton tape on the heat sink, then burnish it (rub it) really well. Rubbing it with a hard edge such as a credit card will make sure any air bubbles are removed and you get the best adhesion possible. Don’t use the corner of the credit card since it could apply uneven pressure and put indentations into the tape. You want as smooth a surface as possible, so start at the middle of the tape strip and rub outward towards one end, then repeat for the other end. Gradually apply pressure when starting in the middle each time. Start the final few strokes near one end and finish towards the other to make sure the middle section is evened out. (Who knew applying tape could be so exacting?! Lol.) Once the tape is applied just mount the device as usual, including using thermal grease between the device and the tape to fill any remaining air gaps. It’s really hard to screw this up, short of leaving a huge air bubble right under the device. Good luck! Edit: I forgot to mention that Kapton tape is semi transparent, which makes spotting air bubbles really easy. When you burnish the tape you’ll see a distinctive darkening underneath it as the adhesive wets the heat sink surface and air bubbles are driven out.

[@slother93]

You can also directly mount to an anodized aluminum surface, which is not electrically conductive. The only caveat there is to be on the lookout for fresh scratches or abrasions exposing raw, conductive aluminum.

[@mystak3n]

Hearing “ground” described as a “reference” is the one thing I needed to finally understand fully what it referred to. Not sure why nobody else had before.

[@RexxSchneider]

At 16:36 To calculate capacitance or ripple, there is a standard equation: Charge = VC = It. That means the current times the time for which it is drawn is equal to the capacitance times the drop in voltage that results. In the UK, we have 50Hz, so the time between one positive peak and the next is 20ms. In the US, that is 60Hz and 17ms. That is the maximum time that the capacitors are needed to supply current. If we draw 1A for 20ms, that must be equal to the capacitance times the voltage drop in that time (the ripple voltage). With 3 x 4700μF, the ripple V = 1A * 20ms / 14100μF = 1.4 V That means the 17V peak of the rectified 12VAC will drop to no less than 15.6V, allowing enough headroom for the 7812 to operate.

[@malcolmhodgson7540]

Great help. Thanks

[@kensmith5694]

Darn. I just explained the same thing before I read your comment. Note: C(I will buy) > C(I need) / (1 - percentage) the typical +80% -20$ cheap capacitor needs to be scaled up by 1/(1-20%) = 1/(1-0.2)

[@igorzherebiatev5751]

But when you use a bridge rectifier, you have double frequency, so not 50 but 100 Hz.

[@RexxSchneider]

@@igorzherebiatev5751 Indeed. So you use 10ms instead of 20 in the formula.

[@terminalwaltz]

This guy really understands how to teach something. Keep up the awesome work!

[@gabrielguimaraes8967]

You are AMAZING, please don't stop uploading.

[@dfautomaton]

I have never understood more how analog electronics worked better than after watching your videos. They are outstanding. Please make many more!!

[@charles.coslor]

Just built a power supply for my modular synth. It's very very simple. There are two 12v wall warts. They plug into a panel with a switch, LED indicators, and a cable running to the bus board. The positive of one connects to the negative of the other, to create a common 0v reference. I think it works fine but I'm leaving things simple so I can improve the power supply in the future.

[@darrenjefferies2598]

Brilliant as usual. The addition of the 1uF capacitor is often forgotten and, most of my 7805 based power supplies don't have one. Also, the capacitor on the output is often thought of as optional. I have made a number of them where I left the output capacitor out to save space and it worked fine... Until it didn't!!. I learned my lesson after that and went to the datasheet where it was clearly stated that there must be a capacitor on the output. If this video was around when I learned this lesson all those years ago, I would not have had to learn the hard way. What I really like about this video is that it covers all of the best practices for design and cuts no corners. Another great video packed with useful information.

[@antiphlex]

I have repaired countless power supplies, but never built one. This is most useful. Thank you.

[@potatothistle]

This is exactly what I was looking for! Thanks for not only sharing the information but making the effor to present it so clearly.

[@ramiro6322]

I'm loving these videos! One thing I would change is the rectifier, you could use a full-wave rectifier at the transformer output so you don't need those giant capacitors to hold the signal for so long.

[@MoritzKlein0]

probably a good idea!

[@psynautic]

came here to say that. i kept expecting him to switch the diode to full bridge

[@bca10101]

From what I understand, if you were to use a full bridge in this scenario, you'd end up with +12V and 0V, and no third voltage level

[@bvcddgtzuii520]

Medi from elektroboom would recommend this too

[@neccron9956]

Normally, you would be correct. But in this case, the circuit that he is using is a voltage doubler. So, you can build a doubler with a bridge rectifier.

[@justovision]

Quick note: I have two different brands of LM7812 on hand. With the ST part the 1uf cap on the output worked fine but on the other brand I saw a sawtooth in the output. Reducing the capacitance to 0.1uf smoothed it out. I need to find the datasheet for those parts but I guess keep in mind that not all 7812s are the same and check your datasheets. I wouldn't not have been able to see that noise without an oscilloscope.

[@BrightBlueJim]

I've seen some datasheets that specify a MAXIMUM capacitance that you can put on the output side, and this does vary by manufacturer. At least one manufacturer provides a formula for determining the size capacitor you should use. The same goes for the very similar LM317 regulators, which are used when you want to use the same part for a number of different voltages, or even a variable voltage. It just requires two additional resistors that determine the output voltage. That "maximum capacitance" can be a problem, because in many cases, the circuits you are operating from the power supply have additional capacitors added to their power inputs. But since that sawtooth you see is caused by the regulator going into oscillation, this is also affected by the inductance between the regulator and the capacitor, and in the case of modules being powered from a power supply, just the wire connecting them together usually has enough inductance to eliminate the oscillation.

[@justovision]

@@BrightBlueJim This is an old post. If you build this I think there's actually too much reserve capacitance and it can kill your AC power supply due to the inrush. There are better options.

[@BrightBlueJim]

@@justovision Nonsense. AC wall warts are just transformers, and nothing else. You'd have to put a LOT of capacitance on it to kill the wall wart, and even then, the rectifiers would probably go first. A lot of commercial audio products use pretty much exactly this kind of supply to get bipolar power to run op amps.

[@johncoops6897]

​@@justovision- NO, because what is supplying the AC is a transformer. At high current, the voltage sags. So when it starts up, the capacitors form an almost short circuit so the transformer outputs it's rated Current and a very low voltage. As the capacitors charge (perhaps 1 second) the current decreases and the voltage increases. Once the capacitors are charged, the current drawn follows the load. You could add a low resistance high wattage resistor as a "current limiter" however the transformer's output windings and the cables from the wall wart to the PSU will do the same thing in real world terms. It might be a consideration for a PCB mounted transformer and 10's of Amps, but for simple low power stuff it is not an issue.

[@Jamie-sy1us]

Really great video. As someone who is just starting out and worried about electrocuting myself to death this has been a great help!

[@brianhagen8244]

Excellent instruction; very clear, well-ordered, and easy to follow!

[@christinamayakovskaya7586]

I never understood physics behind electronics as much as I did after watching your videos!

[@Abossow77]

As an electrical engineer, I WISH I had this channel while I was learning This is better explained and visualized than most classes I had to power through hahaha

[@daviddaigle4841]

Your tutorial videos are the best I've ever/seen, and I have read watched a LOT! I've learned 8 different programming languages the entire Arduino world ect... Seriously Ive read/watched an unbelievable amount of tutorials and your series is honestly the best I've ever seen. Thank you

[@jonathanbecker6373]

Both a practical device I've been wanting, and perhaps the best illustrated analogy for current through diodes and caps I've seen.

[@flflflflflfl]

Thank you so much for these videos! You have a rare and valuable gift, please keep it up. I will be using these videos to teach electronics to my kids, there is absolutely no way I could even come close to your teaching skills. Thank you!

[@justmusicbaby1984]

Thank you so much for the incredible work in your videos, this kind and level of pedagogy is the stuff of the future to me! I'm just blown away by the clarity/quality of your explanations, this is pure light in the darkness! Deep respect from the bottom of my heart man!

[@Galova]

Hello Moritz! Thanks to you I've managed to build an adjustable dual rail psu using lm317 and lm337 with shottky diodes and small trimpots to adjust plus and minus of psu to a desired value. I had no real reason using shottky diodes except their small voltage drop. I have thought that it must provide a broader voltage adjustment range thanks to small voltage drop specially when transformer maximum output voltage is barely sufficient. I also experimented with cold lazer toner transfer to make a small and accurate pcb using alcohol+acetone mixture. I recommend.

[@revoxjazz8317]

Nice way to explain the behavior of a dual rail power supply. Thanks!

[@Francirius]

nice video, very clear and didactic. U said its not a beginner's video, yet u explain the basics...

[@MoritzKlein0]

it's a beginner's video, but not a beginner's project!

[@technodruid]

I would strongly recommend putting two bleeder resistors in parallel with the electrolytic capacitors. Lower resistance for faster discharge, but a 1W 220R resistor would be good for about 5seconds of discharge time to less than 2 volts. The amount of capacitance can pack quite the amount of current in short circuit.

[@Minecraftmigapiku]

but what for? 15V isn't gonna hurt anyone and it's constant power wasted

[@Koen75NL]

Absolutely unnecessary for such a low voltage. Continuously wasting half a watt also.

[@wesleymays1931]

This is a great design for small scales, but linear regulators get really inefficient when they have to push out several amps. I would recommend going switching anyway (ICL7660 to go from +12v to -12v), but smoothing it out by either 1). Making the voltage a few volts too high and sending it into a linear regulator for less noise, or 2). Using a circuit called a capacitance multiplier (transistor buffered RC filter) to filter out the noise

[@ekowwitz]

A great teacher with analogies.

[@martinmartinmartin2996]

(1) "big capacitors" (electrolytic capacitors) have poor characteristics to the harmonics of a rectified sine wave. (2) "small capacitors" (mylar capacitors) are used to filter these harmonics: 0.47uf mylar is cheaper and suitable: to be effective mount close to the L7812 regulator using short leads. (3) L7912 regulator : use mica wafer to insulate metal TAB from grounded heat sink : the TAB is internally connected to negative unregulated voltage.

[@VioletGiraffe]

Thank you for the educational video. This is a very curious design, I would never had though a single diode rectifier could be useful for anything. The most unique feature of this design, apart from its simplicity, is that you get +/-12 V out of just 12 V AC - the output voltage doesn't get halved like in artificial neutral point designs.

[@ttm5816]

Im so happy to see your new vids! So helpful

[@yongewok]

These are fantastic videos - I've been learning "modular" in Reason for years and I've gotten serious this year about getting an analog setup going. I have components, a couple breadboards and an Arduino from taking electrical engineering in college, even though I didn't go very far in it. I recently got the idea of adding a breadboard to my prospective modular rack - initially I just wanted to use it for splitters/mergers and simple logic operations, rather than buying multiple $100 logic modules - but this channel is on another level. My goal when I started learning electrical was to make a synth, but other tutorials didn't really get through to me. I made a sine bass with Arduino, but doing it with ICs on a breadboard is what I was aiming for. I've seen other tutorials, but these go deep, they're clear and thorough and the devices are valuable and functional for music production, as opposed to a tutorial on a single isolated multipurpose component. I don't think I'm ready to mess with a diy power supply yet, but I'm definitely going to do the VCO VCF and Sequencer/Arp and have ordered the extra parts. So dope thanks for your time and effort!

[@jrl924dds]

one thing to note about AC current is that there is a "ground" wire. It's called the neutral wire and is used as a 0 volt reference. instead of a positive wire, AC current uses a "hot" wire which has all the voltage. To tie it back to your water analogy, the neutral wire is basically our ground wire because it stays at atmospheric pressure (a.k.a: ground or 0 volts), while the other hot wire rises and falls in pressure 50/60 times per second around the neutral wire, which creates the sine wave you see when hooking it up to an oscilloscope.

[@Pianodog]

This vid and channel is a gold mind for what im trying to learn. Shame I dont have an oscilloscope, but I should be able to follow ur instructions just fine I just wont be able to check the actual wave forms rn.

[@svg98]

That heat sink looks crazy haha. Yet another helpful video, thanks!

[@sidhenihilist]

Ok, now a video om how to add the +5v rail! Btw awesome video.

[@Rob_III]

Wouldn't that just require adding another "rail" with a voltage regulator with a 5V rating to the 12V input?

[@SpeccyMan]

One small tip. The first C in the word ceramic is a soft C so it is pronounced as an S! Imagine it is a knight called Sir Ramick. ;-)

[@MoritzKlein0]

can’t hide my german descent forever i guess!

[@tehdusto]

@@MoritzKlein0 Your English skills are great - it's just our language that is inconsistent. Sorry about that.

[@beewee1million]

In german it's spelled with a k.

[@beaueatbutterflyyummy4151]

Before he was knighted he was just a young ramic

[@BitwiseMobile]

@@MoritzKlein0 English was German at one time until it was tainted :). Seriously though, there is a lot of crossover between the languages. When I was in HS my science teacher had a German pen pal (this was about 35 years ago :P) and one day I was reading over his shoulder and I actually could understand a lot of the letter! My science teacher was impressed. I guess he thought I was some kind of language savant. I am a software engineer, so languages are near and dear to me, but no, it's just because there are a lot of similarities and I noticed the pattern.

[@FreeCircuitLab]

You could use a powerful op Amp (TDA2030) as a buffer and a 50% voltage divider at input to get the middle voltage level at the output of an SMPS. Still the high frequency noise will be there but it would work to make a 6-0-6 from a 12v SMPS.

[@andrearicci9189]

so many things are clearer now. thanks.

[@assabjorn]

Thank you for all you Learning me i will try to support you 😊

[@aikomastboom]

Thank you for explaining it in so much detail, I learned a lot from this video ( a lot of other information I gathered suddenly fell into place :))

[@paulevans4334]

Been speaking English all my life (native tongue) and I've never heard the term warward before. They are simply called transformers as far as I'm aware. Love the channel and how you explain everything in simple layman's terms makes it one of the best channels I've come across yet. Please keep the simple breadboard circuits coming, they're great.

[@MoritzKlein0]

the word is „wall wart“ - it‘s a nickname i think!

[@johncoops6897]

Wall wart is what Americans call "Wall socket mounted transformers". The term comes from their ugly appearance, like a wart on your wall. n Australia we call them "plug packs", since it is a power package mounted on a plug.

[@gcewing]

You can work out how much capacitance you need fairly easily, by making use of the fact that the rate of change of voltage across a capacitor (in volts per second) is equal to the current flowing in or out of it (in amps) divided by its capacitance (in farads). Knowing the maximum current your supply needs to be able to deliver, you can calculate how much the voltage will fall between one peak and the next for a given capacitance. In your case the maximum current is 1A, and for 50Hz mains the time between peaks is 20ms, so to ensure the ripple is no more than 2V you would need at least 1A * 20ms / 2V = 10mF = 10,000uF.

[@roccotuna]

thanks! If I'm correct, by this calculation, at 60hz you could realistically get away with one 4700uF cap per rail.

[@johncoops6897]

​@@roccotuna- Um, nope. The capacitance isn't halved, it's basically 50/60th.

[@gogotrololo]

i've been terrified to burn my house down with a power supply unit for the last year, and have been sitting on components, not doing anything with them. I came back to this to reflect on if i should get over it, and the line 0:51 to the point of scaling down the voltages......... why was i scared to do this? I'm already working with the right voltages that i am comfortable with for the rest of the projects from the plug itself, this PSU just makes that power stable and usable... if it blows, it'll be no worse than any other magic smoke we come across!

[@kurtkabica]

Thank you Moritz , you make great videos ... awesome

[@DroneDrummer]

Im really new to this. Where do you run the ground cable from this power supply? I see where you connected for the positive and negative rails but im lose on where the ground runs from.

[@kensmith5694]

You have one lead from the "wall wart" that has diodes hooked to it. You have one lead from the "wall wart" with no diodes hooked to it. This "no diodes" lead is your "nominal ground".

[@DroneDrummer]

@@kensmith5694 Thank you!

[@jacobnewcomb9204]

Dammit, your videos are so good. Thank you so much for all that you do!

[@mate_ohd5448]

Hi Moritz ! Thank you this video ! My power supply is 12V AC 1000mA, what 's the thermal resistance I need for the heatsinks please ? What's yours for example ? And if i want to add a fuse after the power connector, I have to use a 1 amp fuse ? Thanks 😊

[@jacobeasoundsystem]

I've never heard dual power supplies be explained so clearly and in so much detail. Thank you Moritz you help make these learning curves much more enjoyable!! I have a question though. Where does the ground go? (0 volts) as there's only the + and - 12v? I'm sure the answer is simple but I can't figure it out! Thanks!

[@sine0]

Yes I came to the comments to ask the question, where is the ground rail.

[@thesaddestcat70]

​@@sine0 I think you arbitrarily choose one of the wires from the wall wart to be ground/0v and treat the other like it is the source of the AC current. I think it's more intuitive if you look at the circuit diagram at 24:00 and imagine the ground connections on the bottom half of the diagram being flipped up to meet the ground connections from the top half in the middle. It looks a lot more like a rectifier when you view it that way. It reminds me of how we think of current as going from positive to negative even though it's negatively charged electrons moving in the opposite direction and you sort of accept that relatively it's the same thing.

[@icebluscorpion]

@Moritz Klein, You are right Ceramic capacitors are non polarized, BUT they have a preferred direction do to manufacturing reasons you have a Hot side and a Ground side. The outer plate of a non polarized Cap should be always connected to ground, if it is connected the other way around then you will introduce HF noise from the surroundings. So please mention also that in the future

[@johncoops6897]

That is totally irrelevant here, since 50/60 Hz is nowhere near RF. You have been watch too much "Mr Carlson" 😉

[@Koen75NL]

Oh please stop it with the cargo cult suggestions.

[@staltarilucio8629]

Love this videos dude, keep up the sick work

[@rokasbarasa1]

Looks very fun. I will try making it

[@mutedsounds2k]

Beautiful. The only problem with 78xx And 79xx ICs is that they do provide very little current out. About 1000 mA, if I remember well.

[@derecwilsom4546]

great video thanks Moritz

[@bvcddgtzuii520]

You can calculate it like a tripple low pass filter,the ic resistance from in to out is the "R" of the filter. 3 time 6db so you got a 18db per octave low pass filter

[@hermannloens1868]

Questtion, since my 1N4007 rectifier diode does not react like in the "Rectification in practice" cahpter: after a short while cuttingthe wave right, the wavemountains drop to no current in my oscilloscope (doublechecked: orientation of the diode, and tested it with a multimeter, seems to work properly). What am I doing wrong? Thank you for help!

[@hermannloens1868]

Uh, I made a bitter mistake: From checking the AC my Oscilloscope was on "AC". In order to see the right graph ("mountains with cut valleys") I had to switch oscilloscope to "DC"...

[@daBuzzY90]

Best channel

[@uhzelectronics]

Awesome!!! Another great video, thank you!

[@supercornatural]

Great video, I love your contant and have build some of your stuff allready, including this power supply. But i think my AC to Av wall wart broke so i want to buy a new one. Which Current would you suggest? before i used 1500mA

[@MoritzKlein0]

depends on how much current you want to draw from your power supply. the regulators are able to handle 1.5 A each. but they‘re fine with supplying less.

[@theVHSvlog]

Hey Moritz, where does the other side of the AC transformer connect to? I did not see it in your schematic but it looks like in your breadboard layout it is connected to the ground rail

[@MoritzKlein0]

you use one side for the half wave rectification (with the diodes, capacitors, voltage regulators) and the other strictly for ground.

[@kaloyankrastev638]

Thank you for all the information! I build a psu similar to this but was having what I considered substantial inaccuracy :11.82 v on the positive. But I see yours is with similar accuracy. Isn't this a problem later, when control voltages are used for oscillation frequency and what not?

[@NathanNoodles]

You can use shunt regulators on the modules to get accurate voltages. Like LM4040 you can use the 10v variant to regulate CV stuff.

[@talideon]

This is where you start learning about the joys of Zener diodes!

[@MissNorington]

I'm working with trying to figure out analog telephone systems, and have seen many of these power supplies using LM317 and LM337. Modern systems use switch mode power supplies but I have no idea how they can isolate and remove the noise! The voltage regulators can't filter the switch mode power supply noise

[@Apollo-p1l]

Ceramic is pronounced as "Seramic" in English. The C is an S sound, Great video and very helpful Moritz.

[@davidvallejo9184]

thanks brother, you should explain the other modules that make up a modular synthesizer, theoretically how you do it

[@ПетрМосевич]

Hi! You’re doing a great job! Thank you) I have a question. Maybe it was mentioned but I missed it. How many modules you can power with such PSU?

[@MoritzKlein0]

well the 7812 can push out 1A at max, and the 7912 1.5A. now it depends on how much current your modules draw, but with my PSU I'm powering around 7 or 8 modules. (keep in mind that some/all of them are shoddily designed and use more current than they'd really need to.)

[@1pcfred]

@@MoritzKlein0 amps is a measure of current flow. Watts is a unit of power. The TO-220 package fixed regulators are rated for a max output of 15W. In the TO-3 package they are good for 20W Amps is the same though. Go figure. What you need to do is look at how professionally made things are constructed. Take a PC for example. They have a PSU that supplies rail voltage and then regulation happens for each circuit block (VRMs). Eventually you'll see the light and come around. With electronics you build a lot of power supplies.

[@oasntet]

@@1pcfred Note that the wall wart suggested also only puts out 1A @ 12VAC; I suspect this will be the limiting factor long before the linear regulators are, due to losses to heat in the vregs and passives. If somebody wants to scale up to a massive rack, it'd be a good idea to either get a professional PSU (something from meanwell, maybe?) or redesign this PSU to handle the higher load. That said, the eurorack community assures me that cross-patching between racks doesn't cause issues as the ground voltages get tied together, so building one of these for every 10 or so modules might also be an option.

[@1pcfred]

@@oasntet powering large projects is a bit of a trick. Expecting to do it all from one regulated source is a big ask. Trying to do it that way you're setting yourself up for trouble. Local regulation is a more realistic strategy. With regulators so cheap and easy to use today it's the sensible way to go. When you look at pro designs they may have a half a dozen regulators on one circuit board. They use overkill to get it done. You have to be comfortable with the complexity when you're dealing with complexity. Otherwise things can get too complicated.

[@hermannloens1868]

Anyone another good source for ac to ac wall warts? The amazon one is not available, in reichelt i cannot find ac to ac ones. Thanks in advance!

[@snopocatepetl]

Fantastic Videos! I'm currently planning to build my own synth, and I'm using your videos as guideline. As I have never built anything with electronics, I have one noobie question regarding the power supply: In your other video, you recommend combining two 9V batteries. In theory, would this also be possible by using two separate 12V DC PSUs? I have a hard time getting a decent AC/AC wall wart whereas 12V AC/DC PSUs are cheap and widely available. Frankly, I would also rather not build a PSU myself at all if possible, since I'm not confident in my skills yet (although your video makes it look very easy).

[@Cesar-ot1xk]

Can i use an old pc power suply that already has - 12v? Or i need to build an dedicated one?

[@MoritzKlein0]

in general, yes, though i would advise that you use a multimeter to make sure the voltages are right.

[@wedkarzkosma]

YOU ARE AMAZING

[@kamidphish]

If you used a bridge rectifier instead, could you reduce the size of the smoothing capacitors?

[@MoritzKlein0]

i think it's a bit more tricky than that because full bridge rectification gives you only two distinct voltage levels to work with: one positive and one negative. so you'd lack the middle (ground) level. i think there's ways to work around that, but i'm not educated enough on that to give more info, sorry!

[@kamidphish]

@@MoritzKlein0 Oh, of course! I did a quick google and it appears you can use a bridge rectifier if you have access to the center tap from the step down transformer, which you don't since, as you suggest, it's best not to mess with 240VAC as a novice. :-)

[@deanolium]

One way to get the ground level is to voltage divide the two distinct levels and rub that through a buffering op amp. Of course the resistors need to be identical, so you’ll need a precision pot, and it’ll be constantly drawing precious current, but it would work more or less.

[@finonomastropiero4261]

0:56 Jameco is just a piece of plastic with a transformer and its thermal fuse

[@69Misterpickles]

Could I put the diode on the +12 side on the output past the cap (facing out) or does it NEED to bridge the voltage regulator like shown? If so, what is the difference?

[@zerstaerker]

Is it possible to use a 8,5A voltage with 3 or 4 of those using high current resistors like those 5W ones they sell at Segor's`to "spread" the current between the rectifier-capacitor-array-modules??

[@SBender36]

really super clear thanks !

[@mcczapens1234]

Hi! Is there a reason for using only one diode, instead of a full wave rectifier?

[@johncoops6897]

The 12V RMS AC waveform is the equivalent power to a 12V DC power supply. However it rises to about 17V then drops to negative 17V in respect to zero volts. Let's say that the total swing is about 35V... By using a single diode, you capture only the positive half of the waveform, and the negative going voltage is omitted. This creates a output that rises to 17V, falls to zero, then stays at zero for the other half-cycle of the AC. The second single diode is in reverse, and captures the other half of the AC, producing pulsed output at maximum of 17V negative. By separately processing (filtering with capacitors) these in the PSU you can get both + 17V and - 17V from a single 12V AC input. You need BIG capacitors because the output of each of the single diodes is complely "off" for half the time, and it's well under the desired 12V for most of the remaining time. Hence it needs lots of storage capacitors on each 17V rail. ... A full bridge rectifier uses 4 diodes and captures both positive and negative half cycles, then combines them together into a output that rises from 0V to 17V repeatedly. It is only "off" for a split second, not half the time like for single diodes. There is twice the power because it's topped up twice per AC cycle, but it's only topped up in one direction to +17V. ... The upshot is that a full bridge rectifier only provides 17V from the 12V AC, whilst the 2 x single diodes can produce 17V plus 17V which is a total of about 35V from a single 12V AC input. The downside is that there is only half the power (watts) on each voltage rail compared to the full bridge which combines both onto one rail.

[@kensmith5694]

@@johncoops6897 Just to throw a cat among those pigeons, there is a way to do a power supply with bridge rectifiers that will get you the +17V and -17V Start by building just the +17V circuit with a bridge rectifier as you normally would. Now get a second bridge rectifier. Hook its (+) to the (-) side of the bridge for the +17V. Get "thumping great" capacitors to hook each of its AC pins to the AC pins of the +17V part. The (-) pin of the added bridge will go to -17V

[@johncoops6897]

@@kensmith5694 - LOL yeah, sounds like a thumping great capacitive dropper. I wouldn't trust such a thing, when there are numerous other ways (like using a proper centre-tapped transformer). Most people don't realise that such transformers are easily sourced from old electronics that don't use a switchmode supply. Old radios and stereo systems are the perfect source for dual-rail parts since that's what they all used until single rail Class-D amps became common. Usually you can pull the mains transformer and power supply PCB and it'll already have the voltage regulators, so you just gotta test/replace the filter caps.

[@MrDudumassa]

the amperage will be as big as the transformer or wich component is the limiter for the amperage?

[@MoritzKlein0]

you have two bottlenecks: the transformer and the voltage regulators. 7812/7912 are both able to push out 1A each (if you use proper heatsinks)

[@MrDudumassa]

@@MoritzKlein0 to increase the size of the bottleneck is needed a different circuit right? thanks for the answer!

[@MoritzKlein0]

@@MrDudumassa not necessarily. there are other voltage regulators that can handle more current. the 78S12 is rated for >2A, for example.

[@MrDudumassa]

@@MoritzKlein0 amazing

[@Cake11223344]

Great as always ! I wondered if I could use 16v 4700uF capacitor also because the voltage going inside is lower no ?

[@MoritzKlein0]

16V is definitely too low because the wall wart is pushing out >17V. it would work for a short while i think, but the capacitor‘s lifespan will be severely reduced. best practice is to use caps that are rated for 2X the maximum voltage going into them, because this ensures that they’ll last for a long time!

[@Cake11223344]

Thank’s ! One last thing, it worked fine for a few days and then the lm7812 stopped working causing the +12v rail to drop to 0, so I wondered what might have caused this ? I replaced it so I will see if it continues to do this

[@MoritzKlein0]

@@Cake11223344 did you attach a heatsink? what were you powering (meaning how much current did you draw)?

[@Cake11223344]

@@MoritzKlein0 yes with a thermal paste too, I was powering a breadboarded vcf (clone of the ms-20) so only one module

[@MoritzKlein0]

@@Cake11223344 weird. breadboard or soldered?

[@themarrowmusic]

Hi Moritz, I was thinking about creating my own modules and/or little standalone mixer and effect pedal. How do I get a dual power supply out of one dc supply like pedal power (9V) or USB Power. Do you got some ideas or knowledge sources I could look up?

[@lucienrapilly6407]

I only have aluminum electrolytic 1uF capacitors at hand, is that an issue? I also have 100 nF ceramic. What's the better choice? Willing to build this now, not to place one more order and wait...

[@MoritzKlein0]

i‘d say go for the 1 uF electrolytics. and use the 100 nF ceramics for decoupling your ICs on the actual modules. that should be decently noise-free.

[@lucienrapilly6407]

@@MoritzKlein0 thanks. and i guess they're oriented like the big caps, + to the ground close to the 7912?

[@MoritzKlein0]

@@lucienrapilly6407 exactly!

[@lucienrapilly6407]

@@MoritzKlein0 Did it on breadboard, everything fine, just soldered on stripboard the positive side and I now get 18 volts... Any idea about what could be wrong?

[@MoritzKlein0]

@@lucienrapilly6407 hard to diagnose from afar, but maybe you have some solder bridges? sounds like the regulator is not regulating.

[@EricBalcon]

Very nice as usual, I just regret you didn't talk about the specs of the 7812/7912, the current they can drive. What type of transformator we can use, how many VA ? what happens if you try to drive too much current out of the 7812/7912 ? is it usefull to also generate +- 5 V in eurorack ?

[@erikr007]

Just one comment on a thing you said at the end of the video... I'm not sure the LM7912 has a built-in protection diode. A diode may be needed if the output capacitance is large enough -- see Fig. 2 of www.ti.com/lit/ds/symlink/lm79.pdf Also, see this discussion on the TI support forum: e2e.ti.com/support/power-management/f/196/t/566228?LM7912-Ext-Diode-for-protection

[@justlavooij]

Hello, as said many times already: your videos are great! I am making this dual power supply but I have a curious issue: the positive rail is +12V as expected but at the negative rail I measure -6V. What am I doing wrong? Thank you.

[@Felipe-gy8gf]

Hello, I appreciate your effort, I am a novice on these issues, I have a doubt, how could I put a LED that indicated when the power module is on? Thank again.

[@MJLouer]

Hi Moritz, great video's and great explanations. I have (some) electronics skills which means that I can read schematics and symbols, but regarding your PSU video. Is there a particular reason that you used three 4700uF capacitors for +12 and another three for -12v ?? will two capacitors for each will do too? thanks in advance for your reply.

[@talideon]

If you can get suitable caps with a value of at least 14100μF, sure, you _technically_ can. All of those 4700μF caps are in parallel to to provide enough capacitance and add up to that. Mind you, finding a pair of caps that big might be difficult: I took a look on Mouser and had issues finding anything with suitable values, because 4700μF is already pretty big as caps go. There are potentially other ways of designing this circuit that could allow the use of fewer caps, such as using inductors alongside the caps for energy storage and smoothing, but that comes with its own set of issues, and I'm not super comfortable dealing with them myself!

[@t1d100]

The 12V Wall Wart that you are using very likely has not much more inside the case than a 12V transformer. Meaning, a bare transformer could be used, with a proper project housing and precautions. Your suggestion to use a Wall Wart is good, because you are teaching people with less knowledge and you want to keep them safe. So, the ready-made Wart housing, wall plug pins and cable is a really good way to go. But, for folks that do not have access, or the financial ability, to buy a Wall Wart, they might recycle a bare transformer from a broken device. Just get some help with doing that from a knowledgeable person, so that you can stay safe.

[@ThePhilStudio]

Just subscribed and discovered your channel once again. Great content.

[@josh156]

How many modules would this PSU run? would it work as a PSU for a whole rack of modules?

[@MoritzKlein0]

depends on how much power your modules need. for me, one of these will power 6-7 modules.

[@kaiserclicker8479]

thx so much for your work

[@marcthenarc868]

I have a newbie question: if this yields +12/-12 voltage and is used in your projects, how does the +9/-9 volts battery setup fare for identical designs (it is even suggested in the EricaSynth EDU instruction sheets). The difference is not thoroughly explained, unless of course there isn't any. 🤔

[@MoritzKlein0]

some things will be slightly off with +/-9V (volume, gate voltages etc), but it won't break the circuit.

[@goodieteabag6665]

I found it nearly impossible to find an AC to AC wall wart. Are they really rare?

[@MoritzKlein0]

yeah, seems like they're dying out. i'll see if i can come up with a more accessible approach

[@TirianMassot]

@@MoritzKlein0 Hi, have you found something yet? I've also been looking for an AC/AC wall wart but I'm finding it very difficult. Some people suggested buying a power bank but these tend to be rather pricy for my use...

[@bostjan3000]

why do we need 35V rated capacitors? Don't they charge to the 12V output that the wall wart provides?

[@MoritzKlein0]

two reasons: first, the wallwart‘s peaks are around 15, not 12V. second, it’s good practice to use caps that can handle at least double the voltage since they will last longer that way.

[@joaomendes179]

Hey! I have been following this series, and I’m really grateful for the knowledge shared! I would like to ask if it’s okay for my ac power supply to be 2000mA? Thank you!

[@MoritzKlein0]

yup, more amperage is never a problem!

[@joaomendes179]

Thanks!!

[@vegansynths7757]

I've noticed in your other videos, you've used the final version of this. But that final version seems to have smaller and less capacitors. Where did you finally end up?

[@MoritzKlein0]

the one i use in other videos deliberately has smaller caps as i use it to only power a single circuit at a time!

[@vegansynths7757]

@@MoritzKlein0 I have so much to learn still. I have built this power supply and will build it again. I’ve used it to power the oscillator 40106 that you made. It’s all working… but it’s noisy. I’ll do some trial and error. Thank you for these great videos.

[@landonreekstin2617]

Is there a reason the 7912 has an output protection diode built in but the 7812 does not?

[@kensmith5694]

It has to do with what falls out of the design by accident. The process of making a chip makes lots of accidental diodes as you put down one bit of semiconductor next to another to make all the transistors you need to make the circuit. In the 7912 it just happens that one of them lands is a way the marketing department could call a "feature"

[@kensmith5694]

16:48 Computing the capacitor is not hard. Here is how to do it. Assume the capacitor is fully charged at the peak of the sine wave call this the V1 Find the voltage that is the lowest the LM7812 will like call this V2 Assume the mains is 50Hz so the time is 1/50th of a second call this T The current is I. How much charge you took out of the capacitor is I*T = 1A/50Hz = Q (V1-V2) = Q/C Do some math C=Q/(V2-V1) Yes, this is a bit inaccurate but the error is smaller than the 20% on a capacitor. Remember to make your nominal capacitor big enough that the one you actually get will be good enough. C(I will buy) > C(nominal) / (1 - percentage)

[@Cray23_Official]

Does anyone know if this Would work for eurorack modules?

[@davidjohnston5329]

Your content is immensely educational, just one 'aha erlebnis' after the other! Keep it up! I just Wonder what the deal is with the small bicycles is in Germany, GreatScott is also constantly talking about micro-fahrrads..:-)

[@stupot7281]

Thank you .. very informative...

[@dusteye1616]

Links to ac wall wart does not work anymore

[@XtianApi]

Why not use one big full Bridge rectifier rather than two separate half Bridge circuits. If you're positive rail has a lot more draw than your negative it's only going to be able to deliver a certain amount of power versus potentially all the power from the sine wave. Isn't that the case? Also you have the small fast-acting capacitors before and after the regulator. Why wouldn't you also want some of the bigger capacitors after the regulator as well?

[@poetadiffidato]

Hi Moritz! I love your channel anda I'm trying to build a synth on a wine box. I used 2 acdc 12v transformer that I have (ones for led stripes) to power the circuit of your CD40106 synth. I plug together the negative and the positive to create the ground. It works pretty well for the process of the first 2 videos until it stop working well. If I plug the circuit sometimes I have perfect saw sometimes I have crazy distorted saw. Maybe I do something wrong or is impossible to power the synth on this way. What do you think about? Thank you so much!!!

[@MoritzKlein0]

haven’t tried powering my circuits this way, so i can’t really give advice here, sorry! did you ground all the unused schmitt trigger inverer‘s inputs?

[@poetadiffidato]

@@MoritzKlein0 yes!!! Maybe there's a diode protection on the power supplies affecting the circuit of the synth

[@MoritzKlein0]

@@poetadiffidato it sounds more like a grounding issue to me.. usually when the schmitt trigger spazzes out it‘s because of fluctuations on the power rails

[@poetadiffidato]

I will try to eliminate this fluctuation! Thank you!!!

[@olbaHB9]

I'm a professional and I don't build a PSU completely from scratch. while I know what to do and what not to do to not get injured or worse, others that might touch/access the connected devices most likely do not. So to safeguard the non-professionals, anything a consumers/lay person can get in contact with I fall back to be safe and use e.g. prefabricated tested and rated transformer coils with the integrated safeguards against touching mains carrying circuits.

[@mz8258]

A little late but how much current does this supply? For the wall wart it says 1.65 A but how does this translate to the two rows? And in case I want to add 5V to the mix, can I just use a voltage divider from the +12V or is it more complicated than that?

[@johncoops6897]

The total equivalent power is the AC wall warts rated RMS Voltage times it's rated Current. So if you have 12V AC 1.65A you have (12x1.65) 19.8 Watts maximum to work with. ... If you use single diodes like shown here you are creating 2 rails (+17V and -17V) totalling 34V, so your current is (19.8/34) 0.58A in total. ... The 7812/7912 are linear regulators that waste the excess voltage as heat, so you don't get that power back when you use them to drop back from +/-17V to +/-12V. ... You also need to allow an overhead and for other losses. The bottom line is that you should allow for about 0.5A on each 12V rail from your 1.68A rated AC Adaptor.

[@johncoops6897]

And yes, you can get extra 5V rails the same way. However the power lost in 7805/7905 is also converted to heat so you can get more 5V power if you take it from the existing 12V rails than if you tap in from the capacitors. ... This is the big problem with getting big current at low voltages from linear regulators like 78xx series. To get 5V from 12V you literally "burn off" the other 7V which makes a lot of heat if you want even 1A output. And you also need relatively huge transformers compared to just getting the power from a smaller one that is much closer to what you need. ... It may be better to create 2 power supplies using 2 transformers, then connecting the final Zero Volt (grounds) together.