FC Power + Modular in a Week. What even is power?

Hullo chaps/chicks

Diving headfirst into the DIY world and this is my first post here. Hi! Great community youse have got here.

Anyway, I have QUESTIONS. Specifically about power and this whole 12v vs 5v business.

So I picked up an FC power supply and that all seems to be working fine.

I’m still waiting on my CEM3340 chip to arrive so I’ve started having a look at Kristian Blasol’s Modular in a week. Definitely a bit more challenging to put together a stripboard but still doable for someone with my rudimentary skills, plus the parts are all available at my local shoppe.

However the thing that bugs me about the MIAW VCOs is how they are powered. Sam’s schematics are pretty clearly labelled with a 12v+ 12v- Grnd etc, plus he also recommends the use of FC Power so no issues there. I’ve investigated how to use eurorack-style ribbon cables for the FC power and going to build my own bus as well.

However the schematics for the MIAW simply say VCC and VEE, and he REALLY glosses over the powering/pins side of things. I didn’t think too much about it until I referred to one of his links → [https://www.allaboutcircuits.com/projects/diy-synth-series-vco/](https://this one from AAC) - where they specifically talk about +/- 5V. But then again I’m not sure whether that simply referring to the CV input? Sorry but this bit confuses me a bit

So this whole thing raises a few questions for me:

  • Can I just use the FC Power and use that for the MIAW modules?
  • Would I just sub the VCC and VEE for 12+ and 12-
  • If not, what kind of thing can I build to step down the 12+/- to 5+/- (would that be added on to the stripboard?)
  • or should I just be building a +/-- 5V power supply?

In the interests of standardisation, I was hoping to just use the bus and ribbon-cables for all of my modules regardless of the source so hoping to find a solution that still accommodates that.

Thanks is advance for any responses!

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welcome :slightly_smiling_face:
some module works with only +12 and GND.
For 5V, normally there is a 5V output on the FC, but I don’t use it and add a 5V regulator directly to each module that needs it.


if there’s no -12 it’s : +12V and GND
some module works with only +12 and GND.

For 5V, normally there is a 5V output on the FC, but I don’t use it and add a 5V regulator directly to each module that needs it.

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That is certainly possible, in fact that is what most people do. So you do not need to build an individual power supply for each module. Building one for many modules is the easiest way to go. Of course that power supply will have to be powerful enough to deliver at least the sum of the currents drawn by the individual modules. Why do I say ‘at least’? That is because at startup most modules draw more current for a short while than when they are running stationary and depending on what modules are doing there may exist modes in which they draw more current than in others. So plan your power supply wisely. Note that quite a few people use (a stack of) surplus laptop power supplies. They often times are quite powerful and can be easily combined into a +12, -12 and +5 combo. There are examples of this shown elsewhere on this forum.

Awesome thanks, this helps a great deal.

So when you say 5V regulator, are you talking about a 7805 or 7905, and just use the 7805 output as the VCC and the 7905 output as the VEE?

Just to be clear, the circuit I am talking about has VCC VEE and Ground, so I’m assuming the VEE is the negative voltage.

Awesome I will certainly look into that, I am drowning in old laptop chargers and work throws them out all the time. I thought teh FC power stuff would be a good one to start with, and would still be useful as a bench/test thing regardless of what I am doing.

RE: current draw, this is something I haven’t given much thought to, is there a heuristic for synth modules? I’ve seen a few calculators online like this one, but not sure whether there is a simpler way?

Most commonly ive seen people using 12v ac/ac 2A wall plug, and recommending using 1 per (1meter) row.
I’ll be using a 1.5A Plug and MiaW’s PSU v2.0 which will be ran through a buss board to power 60cm of Kosmo/Euro.

Ill let you know if i run into any problems when i can get my case built and running. =)

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You can either replace the FC approach by using only laptop power supplies, although they may be noisy ( some people say they carry some high frequency signals that may bleed into your audio, others have had no problems with that whatsoever ), or you can combine the laptop supplies with the FC power stuff. In the latter case instead of using a transformer with the FC-board and a rectifier bridge you can use a laptop DC power supply of sufficient voltage. If the regulator on the FC board is a 7812 then that will accept an input voltage from 14.5 V to 30V

An 7805 will accept an input voltage from 7 V to 25 V.
The 7912 will accept an input voltage between -27V to -14.5V

Note that for 7812 and 7805 choose a voltage as close to the minimum value (14.5 and 7 resp.) as possible to keep the power dissipation low and for the 7912 as high (so near -14.5 V) as possible.

also maybe some answer here

and here

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No, 2/3 of the way down it says

This circuit requires a dual power supply to function correctly (it requires 5V, 0V, and at least -5V on the negative rail).

It’s certainly possible to build modules that run on ±5 V, or 5 V and ground, or ±12 V, or ±15 V, or, well, just about anything I guess. But combining different voltage requirement modules into the same system is complicated. There’s also questions of signal level — some modules create and expect audio signals of 5 V peak to peak (i.e. ±2.5 V), some 10 Vpp, and so on; some create and expect control voltages and gates of different levels. That can get complicated as well.

There’s a somewhat ad hoc Kosmo Specification that specifies these things and others for Kosmo modules, but non Kosmo modules from MIAW or All About Circuits or elsewhere may have different requirements.

AFAIK (I don’t follow that channel myself) the MIAW modules do work on ±12 V and can be used with Kosmo modules. Look at the schematic for one: Dropbox - Schematic_Buffured-Multiple-3x1-2.pdf - Simplify your life. At the upper left it shows the power rails marked +12 V and -12 V.

Same is true for modules from Music From Outer Space. Most Eurorack modules too, but there are a very few that also expect a +5 V rail from the power supply (the FC Power supplies have ±12 V and +5 V, but on mine I left off the +5 V part because it’s not needed for any Kosmo modules). Those one might be able to adapt by adding a +5 V regulator to the module. Modules from https://www.schmitzbits.de/index.html and http://yusynth.net/index_en.php are designed for ±15 V but many can be used unchanged or with a few minor changes for ±12 V, usually they tell you that. And so on: Lots of design sources, some directly usable in a Kosmo system, some requiring more or fewer modifications and complications.


Thanks for your responses everyone and thanks for the links. I think I understand much better now, there is a lot of jargon and shorthand to cut through which can make things confusing at first!

Thanks again