Connecting L.M.N.C.'s simplest OSCs to eurorack busboard

hi, i’m a noob and i m going to start building some DIY modules from lookmumnocomputer but my question is about simpliest vco (ill build 4 together)

this is the personal schematic i draw using the one that lookmumnocomputer has on the page

let me know if some nosense is on :D, i’m quite noob
only different thing is that im buying a transistor which start to oscillate at 9 v so i was thinking for testing to use a 9v battery. (or i need more volts? 12v?)

(by the way the transistor is called Bipolar transistor NPN BC337-40 45V/0.8A
looking for a BC337 i found only this… those other information in the title i have no idea if they fit the circuit :frowning:
using this transistor it still make the circuit a 12v power based circuit right?

how to connect this to the bus board which has -12v using the ribbon cables?

as i understood this circuit use only positive and ground , should i just connect those?
is the system at risk by doing so? do you suggest to better do a stand alone box with its own power supply?

other question:
if i want to have an audio out for each oscillator alone i can just put a socket in the audio out of each of them before connecting them together?? i dont think so because then it will take the audio of the other oscillators anyway… :\ ?

one more noob thing.
with a multimeter how to check if the circuit is good?

no answer :frowning:
i hope somebody can at least tell me this:

using a powers supply block of 12 V instead of batteries which polairty this circuit has? or it doesnt matter (at least not dangerous to try both)?

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It’s as shown in your picture, + is positive, - is ground.

If you use an electrolytic capacitor, connecting it the other way around is liable to make it explode.


Hi there and welcome!
I’ve just seen your post, and I’ll have a go at answering what i can.
Firstly i am unsure about how to answer your transistor question and im hoping others may jump in on that as I’ve not built the sso on anything but a breadboard.

You can run a bc337 with 9v dc but i wouldn’t know if that is enough to make it oscillate. But if you have a bipolar supply +12/-12 you could run +ve to ground for 12v or instead +12 to -12 for 24v which would allow the use of many other transistors. There is a discussion here and a link on sams pages discussing a range of transistors and the voltage required.

The +ve should stay as is in the circuit and connect to the transistors emitter after the large potentiometers output (on an npn that is the left leg as you look at the flat face). The bipolar reference usually just means it can be used for audio which is usually a bi polar signal (picture a wave that goes up and down between a +ve voltage and a -ve voltage around a central 0v line)

Build one. Get that working. Post a pic if you can and then fire more questions if you need to. All of us here are on the same journey and we all remember our first.

If you take a youtube search for the cusi sound channel he has a “little box” drone much like your diagram. It may help.

Crack on and i wish you all the best. Do let us all know how you get on.


thanks for the answers about the power supply block i meant which polarity should be used?

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Either, as long as the positive terminal connects to the circuit point labeled + and the negative terminal connects to the point labeled -.


You could use either. Just make sure that whatever polarity you use the +ve goes to the top edge of your board. @analogoutput 's comment about electrolytic capacitors is worth remembering, though i myself have blown more than my fair share of caps in homage to the blue smoke.



Plus 20 coincidental characters

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im not sure i understood, sorry… been a noob make it difficult to choose even the right words…

i surely understood about capacitor that have the right and wrong polarity (no always as i see, there is some with no polarity, in this case there is) :slight_smile: ill pay attention, thanks

in case i connect a battery i understood that + of battery goes to + of the circuit and ground goes to minus of the battery. all good

Yet i want to understand about using a power block like this instead of a battery or 2 batteries:

the one you can regulate they usually sell with detachable edge and there is two polarity options…

or the + and - is to be set in the socket i should do for this power supply??

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EITHER. As long as you connect the positive terminal of the supply to the positive point in the circuit and the negative terminal to the negative point in the circuit. I don’t know how to explain it any more simply than that.

The two possibilities are that the positive terminal is the one in the center and the negative terminal is the sleeve, or vice versa. You will need a jack on (or connected to) the circuit board to receive the connector. It may be easier to connect it up with sleeve to ground and center terminal to positive (in which case you want a center positive power supply), or it may not, but in any case you could do it either way.

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i think i got it… i was (am) not sure i know how a socket is made according to the legs it has…

like this should be ok right? with center + going to my circuit +12v and ground of socket going to ground of circuit (-)

what about the third leg ? i can just leave it unplugged?


That looks about right, alsothe 3rd terminal isnt needed.


I have tested many bc337 in this type of circuit and many will work on 9v but it isnt guaranteed. With 12v its about 99% certain they should work.


another dumb question…

this circuit can either work with DC power or AC power supply? Batteries are DC so if i wanna use a power supply block i should get a DC one? or it doesnt matter?

Most circuits for modules require DC power with the eurorack and Kosmo “standard” being +/- 12 Vdc.

The first power supply I used to start playing around with modular was a meanwell NSD10-12D12 DC-DC converter, a 220uF cap, and an old laptop power supply. I still use it to tinker.

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but the kit of dopefer for eurorack case that i have use a power supply block with AC.
also one polish guy sold me his psu board and said to use a transformer AC…

does it depend of where im from?

im confused… and afraid now to do anything…

is it actually possible to connect this simple osc module to a doepfer eurorack psuboard with ribbon cable then?

what about VALVE DISTORTING VCA, Simple analog Low Pass Filter, and SIMPLE DIY ENVELOPE GENERATOR by lookmumnocomputer?

is the psu board giving DC current to the modules but the actual psu board is powered by AC supply?

It depends on your initial requirements. If you want a simple bipolar supply to start playing around, I believe that a dc-dc converter is the simplest, relatively cheap solution that can use a 9-36 Vdc power block that most tinkerers have around.

A more traditional power supply would be a linear bipolar supply which requires more components to put together and an AC-AC power brick which are a little harder to find.

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i bought this
for connecting Kosmo’s simplest modules

and this :
to power the psu board…

is it actually possible to connect this simple osc circuit to a doepfer eurorack psuboard with ribbon cable then? or to this psu board that i bought??

what about VALVE DISTORTING VCA, Simple analog Low Pass Filter, and SIMPLE DIY ENVELOPE GENERATOR by Kosmo?

and my question was actually about just using a simple power supply like this for the simplest oscillators box:
to power the circuit in my first post…

should it be ac? dc? or only AC exists liek that?? im checking all the one that i use at home for pedals are AC it seems…

  1. It is possible to connect the simple oscillator to any eurorack psu provided you wire it correctly.

  2. The PSU that you bought provides appropriate eurorack voltages. I’m concerned about the transformer though.

  3. Any properly designed and built eurorack circuit or module should work with any eurorack psu provided that it is wired correctly and the psu provides enough power.

  4. Lastly, a simple 12 vdc brick should work for your circuit in your first post.

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that transformer was suggested by the psu board builder… he specify it need to be AC.

also my doepfer euroack DIY kit “external transformer” is AC…

so i guess that later in the psu board the current is changed to DC before going to the modules since you said that module in general works in DC… right?

sorry for idiotic questions , thanks for you patience guys