5V CV - will Akso be good in modular setups?

Did I read correct that the Akso will have different power rails (3.3v, 5v and 12v)? Will it be able to accept 5V CV inputs and outputs? If it can, I can imagine some very cool uses in modular. It could be a super powerful module in a rack.

Hi @BruttoBello.

Yes, Akso is specifically designed to support CV signals. This is different from Axoloti Core. The four main outputs can each run at line level, bipolar CV (-5V to 5V) or unipolar CV (0-10V). The scale setting for each jack is controllable in software. The inputs are overvoltage protected as well.

You can also power the board at its voltage input pin with rails normally available in a Eurorack system: +5V and +12V are just fine.

Thanks for the response. That’s good to know. Are you aware of it the specifications are the same for the GPIO ports (3.3 volts max)? Also, are there 15 ports (like axoloti) to solder up potentiometers and such? See pic


Hi @BruttoBello. You’ve got the pinout diagram for the Zrna FPAA board here. An Akso pinout diagram is available on the reference page here: https://zrna.org/akso/docs/reference

In general, test points tied to processor GPIO pins, like A0, B0, etc. allow 0-3.3V signals. That is a safe assumption. There are some special cases that will allow up to 5V that I need to indicate more clearly in the documentation. The reference page will be expanded to show the exact legal voltage range on each pin.

The only places where CV signals (-5/+5V and 0-10V) are allowed directly are at the four primary IO jacks and their associated test points, labeled 1T, 1R and 2T, 2R, corresponding to the tip and ring of each jack.

Are the test points labeled 1T, 1R, 2T, and 2R a mere duplication of the option jacks that come with most Aksos ? Or can I utilize the pins as extra CV inputs / outputs ?


Yes they are duplicates

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Thanks for clearing that up lokki. I don’t see any reason to repanel them if that’s the case!

My intention is to make this into a 2hp Eurorack module. I have some questions, if someone (@JoshuaACNewman maybe you?) can help that would be very appreciated as I don’t want to mess this conversion up:

  • Can someone please verify that the 5V pin(s) are for the +5V power? Seems like the best option to get this powered from a Eurorack modular setup. I see two pins indicated as 5V on the bottom left row. Are both to be used for +5V power (see image further below) or just one? Are the ones indicated below the right ones?
  • Which ground should I use for +5V power? Any of the G pins would do? I see a few next to +12 and -12 pins.
  • MIDI RX is mapped to pin G9 . MIDI TX is mapped to pin GE . Do we need grounding for these?

  • :skull: Can I have the module powered by the Eurorack rail (+5 or +12v) AND connected to the computer via the USB port in the front at the same time?!?

I recommend everyone reads the docs, there are some useful things to learn there.


Here’s the bit of interest on Power.

“Akso receives power in one of two ways: from its USB-C device port or from its voltage in pin (+5V-18V). These power sources are seamlessly merged together to drive a primary regulator. They can be applied simultaneously and connected and disconnected in any order. For a Eurorack application, power need only be applied at the voltage in pin, either +5V or +12V from your case supply will work.”


Thank you @blackhill.

I did read the reference but it has left me wanting. It could be far more straightforward in regards to what is what. A simple list for each pin would be far more easy to navigate.

So for instance, there are 5V pins, under MIDI section there is reference to a VI being the Voltage In, and under the Power section there is no mention to the 5V or the VI pin at all. So yeah, sorry if my questions seem noobish, but clearing things up instead of frying the device seems like a better option at this stage.

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Yes, I didn’t mean to be superior, I’m a noob myself. Not everyone knows the reference is there, I only read it the other day myself. I was only talking about the question about the power supply.

It’s hard to find the VI pin, it’s on the right edge of the pinout diagram near the middle.

Definitely worth being cautious about these things.

The first sentence of the Power section I quoted points to the way that the VI pin can handle a wide range of input voltage.

“Akso receives power in one of two ways: from its USB-C device port or from its voltage in pin (+5V-18V)”

It would have helped if he had written instead

“Akso receives power in one of two ways: from its USB-C device port or from its voltage in (VI) pin (+5V-18V)”

Sorry, didn’t mean to sound defensive. I just don’t want to seem like I don’t try to find the info before I ask.
Thanks for the insights.

I agree that the paragraph could be rewritten. The information about the VI should also be under the Power section. And even if pins are documented in the H7 or in Axo site, as per some of the points further down the page, I do think that a full list of all pins ought to be compiled for clarity.


I need some advice from the good people of this forum!

I soldered GE (MIDI send), G9 (MIDI receive) and VI (Eurorack power +12V / +5V) pins:

I think I did an OK job. The issue is I don’t see the LEDs turn on when I try the +5V power.
They do turn on when I plug the USB power cable, which means the Akso is still functional, so I think it’s safe to assume that I did not fry anything with my lack of soldering experience :partying_face:

Question #1: When powered just from +5V pin shouldn’t I also get the LEDs turning on? I assume yes but I’d like to verify as I’m troubleshooting this.

Here’s my cable:

Black goes to +5V and red goes to Ground according to Doepfer mapping. To verify I tried the voltometer and here’s the measurement when I try the cable on a Pod case I use for testing:

Question #2: I haven’t soldered a ground pin so the module isn’t grounded. Is that the issue? Do I need to have a ground pin to get the module to power up from a Eurorack case? Sorry, this is a dumb question, but I don’t really know the answer.

Question #3: Which ground pin should I use for power? There are a bunch of pins indicated with G on the page and it is mentioned that G is ground but does that apply to all G pins and are these all equal or should I solder a specific one for grounding to incoming power?

Thank you so much for taking the time to answer these basic questions. I’m sure other people might run into the same questions so it would be nice to clarify these things if possible!

1/ Normally Red would be Positive voltage. Black would be Ground. Though it does not matter if you switch cable color, so long as it is Positive comming from the Euro rack, and Positive on the Akso are the same wire. Your soldering looks OK.

2/ Yes you need both Ground and Positive from your source to the Akso. I do not have Euro rack.

3/ I would trace the ground on the circuit board with your multimeter, to see all grounds.

You only need either 5v or 12v, and a ground, not both 5v and 12v from your Euro rack if I understood your wiring.

Hope that helps.

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Dave hi, I really appreciate the fact that you took time to answer my questions. There isn’t enough info out there and getting help on this is very valuable to me. So thanks.

In Eurorack red is meant to indicate the -12V at the bottom of the power header and helps with orientation. I wasn’t aware that red goes to voltage while black goes to ground (good to know!), but I decided to use the typical Eurorack orientation of “Red goes down” just to stick to something I’m used to.

Thanks for verifying. I assumed that was the case from what little I’ve retained of high-school physics, but it’s good to verify it.

Excuse the obviously noob followup but how do I trace the ground?
Is it this setting that I have below?

My assumption is that what I would need to do is set the multimeter to that and then touch the pins on the various G points to see if I get a reading. Right? That would mean that both G points are connected, correct?

Absolutely. As you can see from the previous post the reading on my multimeter is ~5V which is when the two test leads are connected to the cable which is directly connected to the eurorack case. So the cable is correct and it provides +5V voltage only.

Follow up for future reference:

All G pins are ground, I used the 200 Ohm setting and verified (disclaimer; I don’t know what I’m doing so I take no responsibility if you use any of the steps I followed). Soldered the closest G pin and it all works!

Now to test MIDI and the other stuff. Yay!

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That’s the correct way to verify that all G pins are connected; most multimeters these days have a continuity tester which beeps, which makes it even easier.

Also worth noting. It would be sloppy board design, or a faulty board, if there were multiple instances of a label (like G) that aren’t connected.

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I didn’t realise this, useful to know that this applies uniformly and not just to common ground. So the +12v are all on the same rail as well for instance.

According to a far more knowledgeable person than I “Sometimes there are multiple grounds on some devices (analog ground, Digital ground, audio signal ground, power ground, etc) so some may not exactly work the same.”.

I didn’t want to take it for granted that a G indication meant ground, and that all grounding pins were created equal. Better safe than sorry! :slight_smile:

Yes the original akso had multiple grounds for different circuitry i think there were 3 analog ground, digital ground, and normal ground. I think it to control noise in the audio sections of the board.I’m not sure if that design comes over to this new board, however.

It doesn’t seem to be the case @Tim, as they all seem to be connected.

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