Interface Mod Duo X with bipolar CV -5;+5v hardware?

Using MOD devices Setup Questions
#1

Hi people.

There is an campaign starting next week on Kickstarter for simple breadboard based hardware CV modules (https://microrack.org/)

I am quite fascinated, and probably would try to hop on that train. I am unlikely to get any actual music from it, but still looks like a fun toy to play with.

On top of that - as soon as my Mod Duo X has CV inputs/outputs, CV plugins and Cardinal, and midi<->cv conversions - there is a potential to combine these actual hardware modules with emulated ones, compensating for every missing hardware module, using is as sequencer, for example, or making some integration with my MIDI BLE flute via MDX and CME USB dongle, and so on.

Problem is - Microrack modules are supposed to work with bipolar -5;+5v signals:

https://microrack.org/#faq

Is MICRORACK compatible with other modular systems?

Yes, MICRORACK is designed to be compatible with other modular systems, including Eurorack. MICRORACK modules are powered by +12V/-12V and work with +5V/-5V signal levels. We’ve designed simple 3x3.5mm Jack adapter module and in addition we offer a Rack Chassis add-on that allows you not just to have portable modular unit but also to integrate MICRORACK modules right into your Eurorack case and setup.

Meanwhile MDX uses 0;+10v unipolar:

https://wiki.mod.audio/wiki/Duo_X_Technical_Specs

Note:

  • On the Duo X Limited edition, both the CV inputs and outputs have a range from 0V to 5V.
  • On the Duo X normal production edition, both the CV inputs and outputs have a range from 0V to 10V.

ADC uses https://www.ti.com/product/ADC122S021 DAC uses https://www.microchip.com/en-us/product/mcp4922

Important Wrong use of the CV ports may damage the MOD Duo X. Please pay special attention.

What can I do to interface MDX with that Microrack hardware and make sure that I would not fry anything? (especially MDX, which would be quite hard and expensive to replace)

I have a normal production Duo X.

Thank you in advance.

#2

cool concept

but buh marketing, no video, no audio…
How am I suppose to get triggered by this dry campaign? :stuck_out_tongue:

#3

Hmm, I believe they have instagram account with some videos:

(Not like I am really impressed by the actual sounds to be honest, but it never happened with me in a context of any modular synths so far. I usually find them more funny to tinker and watch than actually pleasant to listen, so I might be a wrong person to judge. For the pleasant sounds I would rather prefer scrolling Arturia Pigments presets. In case of Microrack I am more interested in the beauty of their technical concept. And hooking up that stuff to arduino)

I am aware of them only because at least some of the developers are located in the same city as me right now, so Microrack news appeared in some local nerdy Telegram chats, and I had seen some videos and concepts there for a half a year.

Kickstarter campaign have not started yet actually, maybe they are going to add media to kickstarter page later? At least I hope so, for the sake of their success. But that’s just a guess, I do not really know the guys personally.

Anyway, I still hope somebody on this forum knows how to connect Duo X to -5/+5 CV signals, so I would be able to play with it in case if I would be able to get these modules.

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#4

Agreed, the prospect of being able to create some kind of hybrid setup sounds promising

Being a bit of marketing mind it just baffles me that some genius and creative minds fail to take on the outsider perspective in order to

  • make it crystal clear what to expect and
  • incite the spark in people to see opportunities so they geek out, make plans, etc.

If you are deeper into this, you see that rght away but that is only a sub set of the potential target audience.

I sometimes have that feeling about MOD audio and their products too but I simply can’t do their marketing for them for free :smiley:

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#5

TLDR:

I’ve tried to understand what MDX actually outputs on the CV port with an actual osciloscope, and seems like CV output has an extremely low resolution.
To be exact, it changes output voltage in about 2.7ms steps, and therefore, sampling rate around 370hz.

You cannot send sound-like signal that way, only MIDI-CC-like controls stuff, and only quite slow ones.

So far my dreams of using MDX in synergy with a hardware CV modules are looking very very bleak.

That’s how sine wave looks at 40hz:
image

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Quite a pixel art here.

On 76 Hz it does not look at sine wave at all already, more like minecraft characters:

image

After about 125 hz the output frequency is not recognizible at all.

At 200hz it even does not make oscilations to the 0 volt, lower voltage is about 4.5:

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and no signs of the actual frequency:

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Considering all that above -

Looks like all the integration I can have with CV - some almost-constant voltages, passing notes voltage, and quite a slow LFO. (less then 1/10th of the Cardinal LFO plugin range of 1-400hz). Everything else would be lost.

With this resolution I would not be able to use MDX as VCO, or VCF or anything that deals with signal faster than about 30hz.

It is not an osciloscope resolution issue - here I am reading blue 100kHz calibration signal with no issues:

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Length of the step in MDX output seems to be 2.81 ms / 356 Hz:

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I have not seen what resolution MDX output DAC chip supports yet, but I am pretty surprised, in a bad way.

Maybe I am missing something? Is anyone here who actually used Mod Duo X CV output for something? Is resolution that bad something expected?

P.S. Also I never noticed before, but looks like stock VCO/VCF plugins do not have CV outputs, only Audio. That’s kind of another nail in the coffin of this whole enteprise.

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#6

Thank you for your attention to our project!
Indeed, the main voltage range for the micro rack is from -5 to +5V, although the LFO has unipolar mode to operates in the 0 to +5V range, and the envelope generators output signals within the 0 to +5V range. However, if you want to be sure that you won’t damage your device, you can use it just as a control signal source. Using CV in the range of 0 to 10V is absolutely safe for all microrack modules.

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#7

Wow, that was an unexpected appearence.
Thank you for the answer.

So far looks like I would be able to use MDX (with CME USB dongle) as a bridge between my BLE MIDI flute (Artinoise Re.corder) and Microrack. With 0v/+5v range it would be only half of the octaves, but 5 octaves is still quite enough for a flute.

Also I had tried to design some op-amp based solution that maps -5/+5 range to 0/+10 range and back in a falstad simulator here, idea was to implement that as a breadboard mounted module.

However I do not have enough electrics skills to say if it is actually a good or at least viable design.

Also it started to make much less sense, once I found that sample rate of the CV outputs (and most probably inputs by extent) on MDX is around 360hz, which means that I can pass only very low frequency signal through it. Still enough for lfo and midi note.

For anything I would need to process any higher frequency, I would need to pass it as audio, both to and from MDX.

Full Kit has input and output modules, so it might be feasible.

#8

Yeah, shows that @microrack is listening; love it when brands to that :wink:

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#9

Yes, that’s vital. Great contrast with Artiphone (company with also had kickstarted products) for example. Those Artiphone guys do not communicate even on their own forum, and lack of feedback even on high impact bugs (like broken firmware updates on Windows 11) had killed the vibe completely for me, and as far as can see for others as well… And instead of actually fixing the existing product (Orba2 in my case, but it was the same for Orba 1 actually) they just started gathering money for another one new shiny gadget. That was very disappointing.

I like Microrack having signs of the opposite appoach and being good guys.

P.S.
Microrack have started campaign today, BTW.

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#10

https://www.kickstarter.com/projects/microrack/microrack-affordable-and-compact-modular-synthesizer

Yes; with a good video to explain what it actually does <3

I hve some kind of experimental project guitar. Microrack tech could be something to tinker with in that context ^^

EDIT: dropped a post on their forum; asking for peopel there to inspire me with some guitar related use cases that could be fun and useful for me.

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