Digital Noise? , Avid MBox 2 and Arturia Micro Brute

[FakuVe]

Hello,

I've just bought on second hand a really nice Synth , Arturia Microbrute but I have a problem, when I connect it with DI to my Audio Interface (MBox 2) that channel gets noise, is a pitched noise based in 1 Khz mainly which changes when I move the mouse.

The point is that this dosent happen to me when I direct input my Volca Bass , and thats pretty confusing me:

Im using a bad cable 1/8 Jack Estereo to 1/8 Jack Stereo with 2 pinhead adaptors for 1/4 Jack stereo.
The output on the synth is Mono and the input on the Audio Interface is Mono (I assume)
When I connect it to my Volca Bass I just need 1 pinhead cause the output of the Synth is 1/8.

Why dont I hear the noise when I put the headphones directly on the Synth?
Why dont I hear the noise then with the Volca bass? ( I just hear a little bit of white noise with this)
It is a digital noise so I dont think is going to be really related to the audio cables.

Shall I buy a Monster Ultimate USB Cable and a Balanced Mono Sound cable ? (from 1/4 Jack mono to XLR male)


Thank you,

[BertKoor]

Sounds like you experience a mild form of ground loop. The digital noise gets through the audio cable and loops back through the power cable.

You say you connect it "with DI". Do you mean you connect it directly, or do you use a DI-box? Oh, at the back I see a "DI" connector on both inputs. Looking up in the manual what that's designed for... Ah, that's for guitars & bass: high-impedance!

You're best off to buy a simple 1/4" (6.3mm) mono jack-jack patch cable or guitar cable, and connect that to "LINE (TRS)" on the MBox2. Don't pay more than $15 for a simple cable like that.

[FakuVe]

lol I didnt realise that the other socket its for line entry...
I will buy the cable anyways.

Somtimes too much use of the forum kill my own solving problems skill...

Cheers BertKoor, thank you for your help.

[FakuVe]

After buying different cables and trying with them the noise dosent go off.

Options:

Using Microbrute Jack 1/4 Out to Line or Microphone Or DI Input on the Mbox2, it gets these noise.
With Microphone or DI I get -60 dB of noise in its peak frequency. (see the Spectrogram is a pitched digital noise)
With the Line in I get the same noise but -80 dB (best option so far).

Now Im using Micrbrute Jack 1/8 Out (For headphones) to Line In and I get the best results if I connect the connector of the cable (on the 1/8 Out) not fully in , so getting in just half the connector make me avoid that pitched noise (still get a -80 dB white noise on the background and I can barely still hear the pitched digital noise)
So with this I have a louder white noise and I can barely hear the pitched noise and when I raise up the volume of the Oscilators the problem is solved.

Just asking , do you know where the pitched noise come from? As far as I can guess I think is created on the Synth (arturia Microbrute), but is rare as the noise is pitched and it changes according to the possition of my mouse on the computer.
But why that noise dosent sound when I use my Volca Bass?



Thanks

[BertKoor]

Now Im using Micrbrute Jack 1/8 Out (For headphones) to Line In and I get the best results if I connect the connector of the cable (on the 1/8 Out) not fully in , so getting in just half the connector make me avoid that pitched noise (still get a -80 dB white noise on the background and I can barely still hear the pitched digital noise)

If you insert it halfway, the Sleeve (ground) conductor of the cable is unconnected. Aparently there is another ground connection between the devices, otherwise you would not hear anything. And this also proves my first hunch that this is the result of a ground loop: connection of ground through both the audio cable and another path (could be power cables or USB or whatever connection is in common between the devices)

You have several options here to cure it:
1. Get a special "galvanic isolation" device that contains a simple transformer. Alternating current will pass that, but there's no direct connection anymore. This is also what a "Ground Lift" switch on a proper DI box does.
2. Cut the other ground connection between the devices. My guess is in this scenario it's the USB cable, so that might be a bit difficult to do.
3. Make use of the fact that the MBox 2 accepts a Balanced signal on the TRS Line-In jack. This is the most simple solution, essentially identical to what you did when the cable was only half inserted, but properly wired. You need some soldering skills alas to make a cable wired like this:

Code: Select all

    Instrument      Interface
tip     o  ---------  o
ring   [ ]      _--- [ ]
sleeve [ ] ----/     [ ]

On the Instrument side it's wired as a standard Mono jack, but on the Interface side it's wired as a balanced connector with the ground conductor left floating. Best is to connect the cable shield to the Sleeve connector on the Interface side, so you have some form of shielding. But this connection to the Ground is unconnected at the Instrument side of the cable where only the inner conductors are connected.