Power supply: +12V/GND/-12V

Hello everyone :slight_smile:

I’m new to the world of modular synths, Eurorack modules, etc. and I have a question regarding the power supply that I should use.

I built the Super Simple Oscillator and I really love it, it’s really fun! Now I’d like to build a few other modules to make it sound better, so I looked at the “Simple analog Low Pass Filter” tutorial… And I realized that you need 3 wires to power it up: +12V, GND and -12V.

I’ve been building guitar pedals for a while now (mainly cloning existing stuff; basically, I know how to solder but I don’t really understand electronics). Guitar pedals only have two wires on the PCB: +9V and GND. It’s pretty simple: just use a 9V DC power supply or battery and you’re good to go. But I’m not sure I understand this +12V/GND/-12V thing. Could I use a 12V AC power supply like this one (and modify the weird plug to solder it directly to the PCB)? Electro Harmonix EU12AC-1000 Power Supply – Thomann UK

I know that a lot of people use power supplies that are specially designed for Eurorack modules, with bus boards and all, but 1) I won’t build a big rack of modules & 2) I’m on a budget. So a small power supply like this one would be more convenient for me. Would this work?

Thanks :slight_smile:


Eurorack uses +/- 12VDC, so the bad news is that you cannot use such an adaptor directly. The good news is, you can make +/- 12VDC from 12 VAC. You could for example look at the Frequency Central Microbus, that’s a small PSU/bus fed from such an adaptor.

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Unfortunately that won’t work. Because this powersupply is alternating current. This is however used to go into something like Microbus – Frequency Central

So this alternating current (the powersupply your link gives) is being split into +12v (which is provided by the 7812 regulator) and -12v (which is provided by the 7912 regulator) direct current.

I know Juanito Moore uses 2 12v dc power supplies. This would be your easiest and cheapest option I think. He connects the positive of 1 supply to the negative of the other. This would be your ground connection. Then use the negative of one as -12v and the positive of the other as the +12v. (hope my words make sense… can’t find a quick picture) I’m assuming this isn’t used more, because I suspect it would be a noisy powersupply, so some modules might not work as well. (I’m thinking oscillators with v/oct tracking,…)

I’ll try to find some pictures:

(in the meantime someone answered already, but I’ll leave my reply as is)

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Thanks a lot TimMJN & Jokke!

Well that’s a bummer but at least I learnt something :slight_smile:

I’m not sure about using the “2 12V DC power supplies” trick. I mean, I guess it could work, but I really hate noise and interferences, and I might need the V/oct function at some point.

I looked at the Frequency Central Microbus and I found something called “half-wave rectification circuit”:

source: https://wired.chillibasket.com/2020/06/dual-power-supply/

The component list is a bit similar to the Frequency Central Microbus (there are a few differences though, not sure why). If I built this circuit and paired it to a 12V AC power supply, would that solve my problem?


You need to build a rather simple circuit that will take the 12V AC signal of the supply, rectify it, convert it to -12V and +12V DC by using two voltage regulators, and filter it. Like this one at the bottom.

Since you are asking these questions I assume that you are not confident enough to build this from scratch so I would advise you to either buy a PCB to build the circuit or print a PCB using one of those affordable services using an open-source design: @analogoutput has one here, and Arthur Saunier has one here.

Total cost of the components should be around 8 EUR + the cost of the PCB.

The answer is yes, but take extra care because mistakes can result in exploded capacitors. If not sure, you can build this on a PCB to keep the chance of mistakes to a minimal.

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That looks incredibly dodgy!!
If it is cheap and fast, it cant be good…

Well its called a sketchy powersupply for a reason… But how would you know if you don’t try it? You know what! I’m gonna try it…

Why not? The wall wart outputs are isolated from the wall voltage. Voltages are relative, so the -V of one can be the +V of the other. Nothing dodgy about it.

Though whether it’s good or not is another question. Wall wart DC supplies often have poor to no regulation; the actual voltage supplied may depend on how much current you’re drawing. I wouldn’t use this for a synth, but for some simple projects it might be fine.

There are numerous topics here about power supplies, no need to create another one. Right at the top of the FAQ category:

Also, the original post prompted this but it belongs in its own topic:


There is a bit of a difference between the theory and the practise. Not saying it wouldn’t work, because it would actually work fine to get bipolar psu.
Consider that even Juanito said that it is not a good idea, I still do not think that building a not even decent psu is great for someone who is getting started.
But if we forget about that, then sure why not.

Thank you all for your answers! I know what to do now :slight_smile:

I’ll buy a 12V AC power supply and buy/build a ±12V rectifier then. The Microbus Frequency Central seems like a good, simple and reliable option but I might end up trying to build one too.

For all newbies like me: I stumbled upon a video on Youtube that explains how this circuit works, in a clear and simple way: https://www.youtube.com/watch?v=pQKN30Mzi2g
I’m not saying this is the best way to understand this, but it helped me a lot.
Note: you might want to watch this other video first: https://www.youtube.com/watch?v=QBatvo8bCa4 which explains the function of basic components such as resistance, capacitors, diodes, etc.

By the way, I saw this other topic Opinion: Don't try to add stuff to a Super Simple Oscillator - #6 by analogoutput and yeah, I’ll probably end up building a more sophisticated oscillator – it’ll be simpler than the SSO in the end. Still, the SSO sounds really good and I’m really having fun with it – here’s some random noodling: https://www.youtube.com/watch?v=xZq0geQHRR4


Moritz klein is a great teacher and a real valueble source. Do watch more of his stuff…


I’ve been using these for all my ±12V requirements and can recommend them for anyone starting out (or not being willing or able to spend much money). https://www.aliexpress.com/item/32967915016.html

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It’s impossible to get powerful enough AC/AC here in New Zealand so I had to look for alternatives. I found this super cheap module that worked great for me. I ended up adding a ferrite bead and a 10uF tantilum cap to do some further cleaning though I don’t think it needed it. So far it’s working GREAT! I just ordered 5 moar!


4.5-30V to ±5V ±9V ±12V ±15V 3A 30W DC-DC Buck Converter Positive and Negative Dual Output Step Down Power Supply Module

on mine, I also wanted to have 5v so I also used this:


The 5v one wasn’t that great tho, it switching frequency is a bit on the low side but still didn’t give any issues since I’m filtering it anyway.

The benefit of this is that it works with a DC/DC wallwart which is cheaper AND easier to find. Linear regulators are cleaner but VERY inefficient.

Don’t forget Ray Wilson/MFOS simple PSU that runs from that kind of wallwart:
Wall Wart Power Supply (+/-9V to +/-15V)

For my modular project I have bought THIS PIECE (+/-12V SMPS PSU) from AliX.
Also got small modules LIKE THIS ONE from AliX, though must be subject to some surgery as the require voltage from a mains tranny with CT.

The MFOS supply uses a 12 VAC wall wart, not DC/DC; it’s very similar to the FC Power (and my design linked above is based on it).

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Likewise, I find AC/AC solutions impractical here, in France. All you can find are low amperage for high prices. Factor in shipping, and you barely beat the price a Mean Well supply… while ending up with much less current.

Meanwhile, a dual DC wall wart supply… 3 euros a pop off AliExpress, and it seems to work well for me so far.

Even made myself a little PCB to take two DC wall warts, add some capacitance, and distribute it via screw terminals (i’ll release it once i test it in more demanding conditions):


@AnalogOutput: And all these designs fits the wallwart Chopstuck was considering to buy …

PS. The MIDI Ultimate I got from Soundtronics came with a 9VAC (or 12VAC??) wallwart and the +/-12V PSU with half-wave rectifiers. I have installed a suitable mains transformer in order to get rid of the wallwart.

Thanks for the clarification. Your message immediately followed:

so it looked as if you might have been referring to DC/DC.

I have a number of transformers much like this one (9V, 12V, 2x12V, 24V …). These are pretty cheap.

Tranny from Swedish shop