Microvolt 3900 + MIDI KB + A3 + AudioBox iTwo interface

Hey everyone! I bought my first real eurorack compatible hardware semi-modular in the form of the Pittsburgh Modular Microvolt 3900, and I would like to sync it with some patches in Audulus. I am having a bit of an issue making sense of it, due to the fact that the MV has a MIDI to CV conversion interface internally, so it seems like the job of the ES-8 is (maybe) already done for me, in this form. This makes me a bit confused, as most of the forum’s hardware based posts seem to be focused on getting CV out of A3 into the physical realm, doing their thing in the hardware, and then coming around full circle back in through the interface and into the DAW.

I would like to do some cool hardware/software blended patches and record the outcome, like some of my more talented and experienced peers have done. My problem is that I seem to only be able to set up the routing of the signals so my Nektar Impact controller, connected to my Mac through USB, is routed through the MIDI out of the AudioBox with some assistance from a DAW, like Ableton Lite (which I had a heck of a time, and spent well over an hour routing and rerouting signals in the process of figuring out) or Logic, and only when the DAW is running can I get simple MiDI keyboard signals from the controller to the MVolt.

I would like to do something like sending an LFO, clock source, or patch output from A3 into my hardware, but I don’t really know where to begin, or how I might set up the signal routing in Audulus. The last thing I want to do is connect something where I shouldn’t, or incorrectly wire it up, and end up letting the magic blue smoke out of my new synth, my interface, my computer or (worst possible scenario) all of the above. I am treading very carefully due to the common sense, and also brings to mind the warning I was given by @biminiroad when he mentioned that he fried his headphone jack trying to send audio or CV into his iPad by mistake, and would prefer to avoid learning a hard lesson like this myself.

I am prepared with my multimeter and also bought a small oscilloscope which is capable of sensitivity up to 20MHz, but I still feel ill prepared to take on this challenge without the advice of greater minds than my own, and so here I am to request advice about best practices and possible limitations. Is any of what I am trying to do possible? The best I can think of would be to make a function node for the transformation of DSP into MIDI messages, but a) is this possible even?, and b) how will I go about setting up the proper signal routing? Can it be done using A3 or do I need to use the slightly limited AU of Audulus inside of my DAW, and this is the only way (if at all)? I hope some of you can advise. Thanks!

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My man! That is one synth I definitely have had my eye on, as it is like the bigger more feature-rich version of the 0-Coast. Also I gotta say Pittsburgh may not have the flashiest front panels or open source firmware but they NAIL the sound they are going for, especially their filters.

The the only patching taboo is to patch an output to an output (as @biminiroad can attest). Barring that, everything else if fair game.

What DAW are you using? Looking over the manual, it seems like there is a jack on the MV where you can send out a midi CC. So if you set up an LFO directed to that midi CC with something like Ableton’s CV toolkit or Logic’s LFO tool you should be able to sync modulation CV with your DAW. Of course you can also sync Audulus AU to your DAW, which I think gets you where you need to go, correct?

From the manual:

Midi CC
The midi modulation jack(107) outputs a 0v to 5v DC voltage based on the assigned midi CC number. This jack can be assigned to a midi keyboard mod wheel or any assignable knob. The midi modulation jack can also be assigned to a midi CC number used by a DAW for modulation. To set the active CC number, press and hold the edit button(30). The active midi CC number can only be changed when arpeggiator mode is NOT active. While the edit button is pressed, the midi section assigns the active CC number based on the last incoming CC message it receives. Simply move a mod wheel or turn a knob to assign that midi CC number to the midi modulation output jack. The CC number is saved in memory and recalled when the Microvolt 3900 is powered on.


Congratulations on your new instrument! Looks pretty cool. It’s a shame that the Nektar controller doesn’t have a traditional 5 pin DIN plus as well as a USB. It’s easy to get USB to DIN converters but they’re all designed to go from DIN to USB not the other way around.

Currently Audulus can only receive MIDI, not send it. All signals out of Audulus are sent via the speaker or DAC nodes. We are hoping for MIDI out in version 4.
Your AudioBox interface is almost certainly AC coupled which means that very low frequency signals like LFOs, clocks etc. from Audulus probably wouldn’t be output. Additionally, since you only have two channels available you would be somewhat limited in any case.

The ES-8 serves 2 purposes. It provides 8 channels of output and 4 channels of input that are DC coupled so they will pass low frequency or DC signals like LFOs and clocks. Additionally both inputs and outputs operate at Eurorack voltages (± 10 volts). This allows you send a signal from Audulus to the ES-8 and have it converted to something suitable for Eurorack hardware either as audio or CV.

With the equipment you currently have you could send a signal out one channel of the AudioBox and into the external input of the Microvolt which will boost it up to eurorack levels or from the microvolt audio output into the AudioBox, but I would avoid attempting to connect anything directly to the patch panel connections. Since they’re eurorack compatible, the voltages will be in the ±10 volt range and could potentially damage your audio interface. You could theoretically connect an audio output from your AudioBox to a CV or audio input jack on the Microvolt but since the Microvolt is expecting a ± 10 volt signal, the 1 volt or so from the AudioBox line out wouldn’t provide much modulation unless it’s run through the external input first.


Thanks so much for the reply @robertsyrett! I have grown to love the style of Buchla inspired synthesis in the west coast format, while still having mad respect for the Moog methods, and so I knew I was going to get something like the Volca Modular I have grown to love so much, with a little more east coast traditional stylings thrown in to sorta mix things up. I felt like the two strongest candidates were the 0-C and the MV. I spent a long time (like every day before, during and after work, for the last 3 weeks) obsessing over every little detail and scouring the web looking for the best demo videos I could find for both of them to help me decide which one I liked more.

I was actually pretty surprised how much hate the viewers of one of the YouTube video demos were spewing about the fact that the MV is only a “single voiced” (traditional style VCO voices, obviously) synth. I also saw many many reviews from very seemingly narrow minded people on respectable forums who called both 0C and MV “one trick ponies” that you will easily tire of and wish to replace with something better. I couldn’t believe what I was reading. What is the deal with that??? As we both know, the right filter can be a voice (and man oh man you said it, does Pittsburgh have the right filter!!), and so can a loopable slope generator, and that makes each of them have (technically speaking) 2-3 voices in total, depending on patching intent. Is this just a lack of understanding, lack of creativity, or something else?

I could not be happier with what I have now! The one thing that was baffling me about it, without any ability to figure it out on my own, was the fact that I wasn’t sure how to blend my virtual environments with the tangible environment in my hands. Now that you pointed that out (thanks so much, btw :slightly_smiling_face:) I can get back to my adventures. I had read the manual 2x and read that page both times, but I guess I just didn’t quite comprehend that part until you translated it into something a bit more understandable.

My DAW is mostly Logic Pro, but I sometimes get lost in the deeeeeep possibilities of that app, and find myself switching over to the Ableton Lite version I got for free with my Volca Mod. I find that it is true what they say, and that sometimes too many possibilities can inhibit creativity, so using a more limited application can help me to accomplish more. I have recorded 3 of the 4 tracks on my SoundCloud using Ableton lol. I do wish to use my investment in my DAW to the full potential, so maybe this weekend I will sit down and watch some of the videos and read the manual that explain the intricacies of LPX so I can more effectively utilize it. Is the LFO tool you mentioned something I will easily be able to set up? Also, if not, is the Ableton version CV tool something you need to have the Studio or Suite version in order to use (e.g. Max, simplified external instrument profile setup, etc)? Either way, I am really looking forward to using what you so helpfully pointed out. Thanks so much!


If I read the manual correctly the Microvolt will accept MIDI tempo from your host DAW and uses it to control the arpeggiator it looks like it’s also available on the clock out jack so you can send clock from your DAW to both Audulus and the Microvolt .
For LFO you might find this useful:


You could use this to generate an LFO and send it to Audulus via a knob and the Microvolt via the mod output.


That helps so much, thanks @stschoen! I am so grateful that I have this community as a point of reference and experiences we all share as a common interest. I don’t think I could get the same level of knowledge gained in the ~1 year I have been a member anywhere else online or off. This forum is truly unique and the members are all so awesome! Thanks, as always :slightly_smiling_face:

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I think you probably figured it out, but Ableton Lite is absolutely bare bones. Back when I had it, it didn’t even come with Operator. Logic Pro X is an absolute ocean of features though, so if you need to do something specific I wouldn’t hesitate to use the tools you have until you can get the tools you want. @stschoen has already shared the link I was thinking of, so definitely give that the once over.

I’m exactly the same way. Every now and again, I try and ready the octatrack manual and I can go about half an hour before I become physically drowsy. What I find handy is dipping in when I need something specific and just doing a command + F to do a keyword search relevant to my need. Get in, get out, get on with the music.

If I had to guess, the MV was just a little behind the narrative trend of 2018/19. It used to be sufficient for a synth to be analog, then it had to be semi-modular, then west-coast influenced. When the MV came out the narrative had been taken over by Behringer dropping the unit cost of a minimoog model D (3 oscillators) to $300 and popping out the Neutron (2 oscillators) which has onboard delay and a bajillion patch points. The MV didn’t really fit into that so well, being just really nice-sounding and still costing around $650 but being yesterday’s knish with one oscillator and no built-in effects. Notice that the new Voltage Research Lab has multiple oscillators, built-in analog delay, and a bajillion patch points.

It’s funny, even Andrew Huang, while reviewing the SV-1, had this to say about Pittsburgh Synths, “I’m struggling what to say about it because I focus so much on the things that are weird.” Turns out just being a rock-solid analog synth doesn’t cut it like it used to back in 2015.

As with most people just following trends rather than their inspiration, once a piece of gear loses its cool factor it’s put back on Reverb.com and passed along to the next person, who will hopefully find it more fulfilling. Don’t pay it any mind to the haters though. One oscillator synths are pretty much my favorite. I’ve been borrowing a Murmux V2 and while I liked how brash and beefy the full 3 oscillator voice was, when multi-tracking I found I would be better off using just one oscillator for layered parts. It’s like drawing with a nice ink line instead of a course charcoal stick.

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To reit mr. schoen… You need a DC coupled audio interface in order to send cv signals between a modular synthesizer and a computer/ipad/phone.

That’s correct. Most audio interfaces are AC coupled which just means they won’t pass very low frequencies including static voltages. My Focusrite rolls off below 20 Hz. This is done to prevent potential speaker damage caused by subsonic signals. The second challenge with connecting eurorack style CV with an audio interface is the different voltage levels used. Eurorack CV signals are in the range of ± 10 volts. Eurorack audio is more typically ± 5 but this varies between vendors. Both of these are much higher than a typical audio interface is capable of handling. The maximum output voltage of my Focusrite is around 2 volts.

The trend is toward using MIDI as a means of controlling a hardware synth rather than CV. While MIDI has the disadvantage of rather low resolution (128 steps for 7-bit MIDI), it’s fairly cheap to implement and MIDI controllers are widely available. MIDI support is also built into most popular O/S’s so connecting a computer via MIDI is fairly simple. Additionally MIDI provides clock which can sync the software and hardware tempos.

The Microvolt is a good example. It has a MIDI interface capable of receiving both MIDI note messages and MIDI CC messages which gives you an easy way to connect a keyboard and a single channel of modulation. The onboard external audio input provides a means to boost incoming line level audio to the necessary voltage to work in a euroack environment and the output section is designed to produce line level audio out. Although you’re limited to a single channel of modulation all the basic elements are there.

Unfortunately the number of DC couple audio interfaces is rather small. MOTU still makes some DC coupled models but Expert Sleepers models seems to be the most popular. MIDI to CV modules are also available and are generally cheaper than DC coupled audio.


@futureaztec at first I was like “wait, I think you may have read into this a bit more than what was mentioned, as @stschoen said a bunch of really helpful and specific things, but I don’t recall that being one of them. I thought I inferred it from his other messages…” and then I went back and saw the post reply immediately following @robertsyrett’s first reply lol.

It may have seemed odd that I only thanked him for the reply, so I apologize if I seemed like I was disregarding what you were saying initially, @stschoen. Apparently, both posted replies came up at very close times, so I didn’t even see a reply from you until the one in which you very thoughtfully provided the alternatives from LPX for my purposes :slightly_smiling_face:

Thanks so much for all the replies, everyone! I feel a lot more prepared to work with this as an extension of my software (although it would be nice to be able to mix signals from A3 with my hardware). I am just hoping the new A4 release will have MIDI I/O for those of us who don’t have the ES-8 interface (yet lol). If anyone can think of a workaround specially for this hardware to work with A3 right now, I will call you the grand champion wizard of my recording world! If not, nbd, and I will just have to wait for A4 with fingers crossed, and I will be fine either way; there is already so much that I am lucky enough to be able to incorporate into my work :smile:

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VCV Rack 1.0 has MIDI out. Then you could handle the midi in your DAW and still have some interesting software modular synthesis.

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That is an awesome idea for a temporary fix! Thanks for that, as it will do the trick for the time being until: a) I collapse and buy the ES-8 (but I don’t yet have a rack of/for modules, and I might be opening a much bigger can of worms by having a nice rack with no modules in it to go with the nice, shiny and useful ES-8) or b) A4 comes out and I end up buying that instead. I also had examined a bit, but haven’t yet fully considered buying Gadget for Mac, as I already have it for my iPad, but I think that might just be a $200 investment in something for which I already have a solution, even if it is not entirely the way I would prefer it to be. I probably should just cling to option B with a deathgrip, since I have more sense than what I am currently sitting here thinking about. haha. Anyway, your suggestion will work awesome, thanks again! :smile:

As you say, the ES-8 might be too much of a temptation since you would need a case, but even factoring a small case, it’s the most cost-effective DC coupled interface I’ve found. If you go the MIDI route, the FH-2 is a very capable solution although you have more choices available for MIDI to CV conversion. @futureaztec brings up an interesting point. It would probably be possible to send CV signals from Audulus to VCV Rack, convert to MIDI and send to your Microvolt (assuming you CPU doesn’t choke trying to run everything at once. Ableton and Reaper have no problem passing DC signals, so I suspect that Logic will do the same. I’ll have to give it a try and see if it will work.

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Unfortunately it doesn’t look like the VCV bridge will output MIDI, so you could use VCV Rack to generate MIDI but it would have to be standalone.

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Are you sure? I am not in a position to test it but: https://vcvrack.com/manual/Bridge.html

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It make sense if you think about it. The VCV fx VST bridge is an audio effect, not a MIDI effect so the DAW isn’t expecting to route MIDI out of the VST. You would need a MIDI effect version. At least I couldn’t see any way to do it.

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Here’s a nice video for the MIDI in/out on VCV Rack. Should help with integrating the Microvolt.


I just stumbled upon the Doepfer Dark Link today! Is this perhaps something that will fit my needs? Granted, it’s no ES-8, but it also won’t end up costing my very tempted self a couple thousand overall. At least for the time being…
What do you think? :thinking:

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What about cv.ocd?


Thanks for the reply. That is a nice looking unit, and the price is pretty good, but I am set with the MIDI > CV inside my MV 3900 for now. The thing I really wish to do most (and that is so complicated right now), is to interface my hardware with Audulus, due to the fact that it will do CV out with the ES-8, but it does not yet do MIDI out. :confused: Do you know of anything else that is a little closer to ES-8, not rack mounted, and perhaps a little less expensive than the Doepfer unit I referenced above? That is really what I am looking for, currently.