I want to build my own syth and am looking for the power draw on a “standard” setup. I.e 3 vcos , mixer, fm maybe a sequencer and much more. Any ideas?
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I don’t think anyone has a standard setup, but if it were me them I think +/-12v at 1A and possibly a +5v 1A rail if you are going to add digital stuff like a sequencer. My own personal setup is a simple +/-15v 3A from two 15v supplies in series. I tend to build modules in the +/-15v range, whereas I think Cosmo and euro rack modular use +/-12v . I also regulate any 5v requirements on the modules.
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Hi Chip, i use +/-12v for my synth and used the psu schematics from @EddyBergman
Its a full wave rectified (4x 1n4007 diodes) psu using the LM317 and LM337 regulators. Easy to build, very stable.
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Modules draw very little current. You’ll be hard pushed to find a module that draws 80mA so you can hang a lot of modules from a 1 amp powersupply. If you use LM317 and 337 with some good heatsinks you’ll be good to go for a 15 module setup. (most will draw about 20 milli amps. but you don’t want to go to the limit with these voltage regulators. You need to leave them some headroom.) My system has a dual 15V and dual 12V rails in one so I can give each module the power it was designed for. And it’s fine to combine them, no problem.
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LM 317 337 rather than 7812 7912 and 7805?
My first PSU was build with LM7812 and 7912 and works fine. The 7812 outputs 12,36v and 7912 12,14 which should’nt be any problem at all but the LM317 and 337, are ones that you can adjust with a 10k trimpot. You can trim them exactly the values that you want between lets say 5V and 30v (depends on what transformer you’re using) 30v is the max input voltage i believe.
I use a toroidal transformer with 2x 15VAC, 2amps (sometimes i get 17VAC), which is sufficient to use. After being rectified you get 22,3VDC which then will transformed down to whatever you want using the trimpots.
Hope this info helped?
it all helps, I’m new to this sort of pcb design. Done a few kits and once made a valve guitar amp (so hars wired) I have a 230v ac 15v -0- 15v 80va toroidal amp. I know the dangers of mains electricity. Chip90125/PSU: creating a PSU
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This is the schematic i used for 3 modular cases
I only use 6x 3300uf electrolytic capacitors and changed the 15k led resistors for 2.2k ones.
Credits ofcourse to @EddyBergman 
You don’t need a toroidal transformer (which is quite pricy) for a synthesizer linear PSU. A regular transformer with a 2-3A 12V secondary will do the job fine. For that setup, you can go with the LM7812/LM7912 regulators as in the design Ray Wilson/Frequency Central design. @analogoutput has a similar open source version here.
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A good PSU is important so i didnt mind to spend more money on that. Toroidal transformers are known to have less magnetic fields than conventional shunt transformers so i thought, why not use those:sweat_smile:
I take it you used some inrush current limiter or did you tell your diodes to toughen up?
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I would use a minimum of 3v over so for a 12v supply use a 15v transformer
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4x for input and 2x for output to keep things stable especially VCO’s. I did had some issues before. Drifting VCO. So when i added more caps the issue were solved as if some sort of power buffer was needed to keep voltages stable. Thats why i used 2 additional caps.
Yep, ive had some issues in the past that the positive power regulator did not start. That was solved by adding a diode across ground and the output. When i build my first PSU i used an 2x 12v transformer i had laying around and did output 14,2v after being rectified wasnt just not high enough to start the regulator.
It seems that this is a typical problem, also discussed here.
12V AC after rectification should be plenty for the 7812 regulator. I think that using a 15V AC transformer is an overkill, considering the excess heat and the need for 25V rated capacitors which will probably not fit on the available PCBs.
Rectifying 12V AC should give almost 17V so that doesn’t sound right. I suspect that there must have been something wrong with the transformer, or you might have gotten one which had more loses than typical.
Of course, toroidal transformers are better/superior, but unless you are dealing with audiophile/high end audio, these features are not really needed in a modular synth. Many (most?) modular synths even use switching PSUs and they perform fine, so I regard using a toroidal transformer in a synth PSU an overkill.
I mean, I am not to tell people how to spend their money, but just saying for the sake of the discussion since other people are probably reading this 
Personally, I use a regular 12V AC (rated 30VA) transformer (made locally by Amarad and sold with the intended use of… heating beehives) and the 7812/7912 regulators PCB by Arthur Saunier. I built two of those without any startup or noise problems.
I recently got a high end toroidal transformer by Giatras, but will likely not use that on a synth PSU. I am thinking it could be more useful in a (tube) amplifier project.
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12v AC after rectification is not AC anymore, and if you put 12v into a 7812 then good luck with that. When you start to load the circuit you will see a dip on the input to the regulator, in all my 40+ years of repairing synths all the transformers are rated 3v over the supply, but what do I know.
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looked at the schematic slight variation found on Synther Jack’s page. what would be the trace thickness be 2mm?
Hi, yeah your right. Its overkill maybe but 35 euro’s for a toroidal 2x 15vac transformer is not that expensive imho. Thanks anyways for your detailed explanation. I appreciate it as theres also information in it that i didnt know so thanks for that.
I try to use as much the legs of resistors/capacitors as connection traces.
Just bend them together. Will send you a photo later to show how i did it
12V AC after rectification becomes ~16.9V DC which is 4.9V over 12V, which is well over 3V, so the 7812 will work and regulate as intended. No luck and neither 15V AC is needed.