Volca Modular CV w/ Audulus

#1

Hey guys!

I was wondering if anyone could tell me about the CV standard(s) and whether or not my iPad can send CV out through the headphone jack into my Korg Volca Modular? Or is there some other hardware that is necessary?

I am having a heck of a time finding an answer that doesn’t include the word “probably”, “hack”, or “mod” in it. If it is possible, I would like to know what kinds of cool things I can do that I have not been able to do, prior to getting this neat USB interface for my iMac and wonderfully amazing little semi-modular science kit that makes me feel like I am on a scientific adventure into the land of electrical theory and physics of sound every day when I get home from work.

If not possible, I would still like to better understand how CV works, so any and all links, periodicals, lectures, or videos you have to provide or of which you can point me in the direction, I would love to know more about! :wink:

0 Likes

#2

Headphone jacks are designed to block unchanging CV, which in an audio context just messes up your speakers and headphones. So it’s not really possible without some extra hardware.

The CV.OCD is probably the least expensive way to get CV out of a computer using a new product. Unfortunately it is a midi to CV box, so if you want to use it with Audulus it will have to wait for Audulus 4.

An ES-8 is a good option, but is like twice as expensive as the volca modular and still requires a powered case to make it work.

Basically what you are looking for is a DC-coupled Audio interface. While they are becoming more common as people have a lot more CV compatible gear they want to computer control, but they tend to be at the high end of the market. Interestingly old MOTU interfaces were DC coupled (not sure why exactly) and you can usually find them used on reverb.com, but be warned a lot of them are firewire devices and are a hassle to use because the drivers are old.

1 Like

#3

I did find an app that claims to generate CV through the headphone jack, however it’s only capable of generating +/-0.5 volts. Normal Eurorack CV voltages are typically in the +/-5 volts range although there are differences between manufacturers. The Volca manual states:

CV–IN jack
This jack allows you to connect two external control voltage sources to the volca modular. The left channel (tip) of the input is clipped to +/-5V and scaled down to +/-3.3V, whereas the right channel (ring) of the input expects a 1V/octave signal (0–+6V) and converts it to the volca modular’s internal pitch offset voltage control signal.
As @robertsyrett mentions you will need a DC coupled audio interface to get CV from your iPad using the current version of Audulus, and there just aren’t many available, but a MIDI to CV converter will work with apps that can send MIDI.

2 Likes

#4

You can probably use it to send gate signals out, but I’d be wary of sending anything into your iPad through the headphone jack. I did once on accident and I fried my input jack. You’re better off getting an interface like suggested above :slight_smile:

1 Like

#5

I’ve used my iPhone to send gate signals from the headphone jack, but it needs to be amplified to be used with modular signals typically.

1 Like

#6

Ok, so I have been researching this for days, and if I am not mistaken (which is a distinct possibility that I am very), that the 0-+6v control signal is actually converted to somewhere in the range of +/-3.3v to make it an interchangeable signal, it seems, unless I am completely misunderstanding. This is the manual entry set where they mention it, but don’t make it entirely clear:

I know a fair but about electrical, but my training was more specifically focused on 24v low voltage control signals at the low end for the relays that close the circuit to allow up to 3-phase 440v that powers the HVAC commercial chiller units I went to school a long time ago to learn how to install and/or fix. I feel pretty confident wiring up anything and everything in that range, and yet something about modular scares me. I think it is the way it seems to be a loosely suggested standard without any real enforcement that seems like it could result in a heartbreaking cloud of the magic smoke that makes the circuit work correctly getting released from inside my synth.

I don’t wanna blow up one of my favorite things in the whole world, so my question is this: is it safe to use the +/-0.5v signal from the iPad headphone jack for all things in this unit, if the manual says that a +/-3.3v signal can be patched to anything in the unit? Are these types of things (sometimes) protected from dummies like me making “uh-oh” situations? It seems that way, especially because of the part where it mentions using the mono TS cable, which will result in the same signal (presumably bipolar) getting introduced to what is listed in the manual as a DC expected patch point. I’m looking for reassurance or advice about “why not”, if anyone has the inclination to help me to understand this a little better?

2 Likes

#7

As @biminiroad mentioned, feeding signals into the iPad microphone jack is probably not a good idea. I don’t know what the physical limit is, but the typical mic signal will be in the millivolt range. The headphone output from the iPad seems to be limited to about +/- 0.5 volts which is sufficient to drive a set of headphones. I don’t think you would be in danger of damaging anything by sending this voltage into the Volca, but it might not be sufficient to create very much modulation. The manual states that the CV input is clipped at +/- 5 volts which is then scaled down to 3.3 volts. I would guess that the scaling is probably just a resistor network, so it’s likely that the +/- 0.5 would also be scaled down. In any case if +/- 5v is 100% modulation, your maximum possible modulation would be about 10%. If you sent the 0.5v into the 1V/octave input, you could cover about 1 octave (+/-0.5volts is a 1 volt swing). I wouldn’t use a mono cable unless you wanted both the CV and pitch to track each other. A stereo cable would provide separate signals for each input.
Actually I’ve been thinking about this and if the headphone out jack is DC coupled (which appears to be the case at least on the Air 2) in theory it would be possible to build a DC coupled amplifier circuit to boost the voltage up to something a bit more usable. I’m kind of surprised that no one in the modular community has done it (at least not that I can find).

2 Likes

#8

I found this on Amazon


It’s a high precision DC coupled variable gain amplifier. Looking at the datasheet, it would probably be just what you need to boot the headphone signal. The gain can be set by an external resistor from 1 to 1000. If you chose an appropriate potentiometer, you could even make it adjustable. It does require a bipolar supply, +/- 12 volts would be best, although it would work at +/- 9 volts for this application, if you wanted to run it from a pair of 9volt batteries. Best of all, mounted on a board it’s only $9.99. The frequency response is flat to over 20k so it would also do audio rate signals. Here’s the data sheet for the IC

4 Likes

#9

Awesome find, @stschoen!! I appreciate you mentioning that so I could make this work. I probably should just write Amazon a blank check at this point, cuz there is nothing I can think of that they don’t have for me :slight_smile:

2 Likes

#10

It occurred to me that if you have a headphone cable and a multimeter. it would be a simple matter to verify whether the iPad you have will output DC voltages from the headphone jack. Load up Audulus, connect a knob to a DAC or speaker output and measure the voltage between the sleeve and tip or ring of the cable. With the meter set to 1 volt DC you should see a voltage change as you move the knob. Make sure the meter isn’t set to Ohms since that would apply a voltage to the cable. If I recall correctly the tip is the left channel and the ring is the right, but I might have that reversed.

3 Likes

#11

Thanks so much for all of your help in my quest to make sense of this whole concept :smile: You are correct, the tip is the left and the ring is the right. I was actually poking around with my meter the other day, trying to do just that before you mentioned it, but my hands slipped while trying to hold too many items and pinch the jack between my two needle point leads and I nearly dropped my iPad in the process, so I gave up since I didn’t really feel like I was certain about what the outcome should be, at the time.

So tonight when I got home from work, I got my meter out again, knowing now what I was looking for. It appears the iPad is not capable of doing DC out, however it is outputting voltage with a sine wave LFO connected to a DAC node, which is steadily cycling between 0-1 at 0.25 Hz, and the iPad, (with the volume turned way down - not sure if that makes a difference, but it seemed worth mentioning) is pushing out an AC voltage swing of -0.130 - +0.130v, so it seems to be doing something. How significant or shrug-able that is, I’m not entirely sure. I just wanted to be certain to report back with what I found in my testing.

Oh, and also, I found an app call CV Mod that has two oscillators that each are capable of putting out a control voltage through the headphone jack on each opposite stereo channel with a TRS cable plugged into the headphone jack, and (while not enormously different) it is able to modulate the parameters of the Volca Modular a noticeable amount on both connected channels, despite the fact that the right is expecting 0 - +6v. I found that to be pretty neat, and the thought is just occurring to me in this moment, but if I am detecting AC voltage cycles coming out of the headphone jack with just an LFO connected, then this would mean that Audulus is also capable of sending out CV then, right?

1 Like

#12

Interesting that you would see an output at 0.25 Hz and not at 0 Hz. A 4 second cycle time is more than long enough to be useful as CV. With a bottom end so close to zero, the iPad must be blocking DC output digitally rather than by using an in-line filter. Maybe the iPad won”t pass output that is unchanged for longer than some set period.
You should be able to set up an LFO in Audulus and output it to a DAC and get similar results to CV mod.

2 Likes

#13

Well, in that case I certainly feel like a dummy, having spent $2-3 on a new app just cuz it specifically mentioned CV in the name and had such high ratings. Fool me once, I guess…at least I know now, and so will anyone else reading this thread, so we will all be aware that there is no need to buy another app for the iPad/iPhone to output CV, and you will actually have more control over the Audulus parameters than CV Mod, I believe.

1 Like

#14

It never hurts to have more options. CV Mod was the app I had mentioned earlier. It looks like a pretty capable app and since it will run on an iPhone you might be able to pick up an older phone with a headphone jack and have another CV source. Looks to me like like it’s worth 3 bucks.

2 Likes

#15

I wanted to post about the results of my testing last night. It is really exciting stuff for me!:

I set up a waveshape LFO (courtesy of @robertsyrett) connected to a DAC for each outbound channel from Audulus on my phone, turned the volume way up, and it was outputting enough CV through the TRS cable to be noticed and have a really cool modulation effect on my sequencer playing the scale notes. I will try to get a good video of it in action this weekend, so you can see how well it works. Thanks so much @stschoen and also to anyone else that chimed in with helpful advice or suggestions to make me feel confident that I wouldn’t blow up my new synth.

I am so happy I found Audulus and became a part of the community, as I have learned so much and have not encountered a more helpful and engaging group of users than here, anywhere else, online or off. This is truly a unique and special thing and I am really glad to be a part of it :smile:

4 Likes

#16

Cool, I’m glad it’s working for you. I’ve also really enjoyed my time with Audulus and all the fine people in the Audulus user community. It’s great to hear everyone’s point of view and see what others come up with.

2 Likes