SEARCHING: audio interface with 4 separate channels

[Wonks]

I was considering that, but wasn't sure how using the Hi-Z switch would cure it?

[Hugh Robjohns]

Difficult to know without knowledge of the circuitry and board layouts, but it would certainly involve a separate unbalanced amplifier stage, possibly with a different ground reference point.

Other inputs are balanced and so with an unbalanced input the 'ground' signal is being fed directly into the amp stage.

[cremedonut]

Is this of any help?

[Wonks]

Unfortunately, no. They are just the functional block diagrams from the manual and show a mixture of software and hardware functions. It's the full hardware circuit diagram that's needed to tell us exactly how the grounding is arranged.

But what is your full setup? Have you got a laptop or a desktop, and is anything else you have connected to your recording setup powered directly by 230v, rather than by a double insulated PSU? It may well be that there is no solid system connection to ground.

If you've got a multimeter, you could check if there's a low resistance (less than a couple of ohms) from the outer case of a metal jack socket or XLR plugged into your interface, to the ground pin on a wall socket. I presume you've got Schuko sockets, so the ground pins should be easily accessible.

[cremedonut]

But what is your full setup? Have you got a laptop or a desktop, and is anything else you have connected to your recording setup powered directly by 230v, rather than by a double insulated PSU? It may well be that there is no solid system connection to ground.

I have observed the issue on both a laptop in battery mode (nothing connected but the interface) and on a desktop pc. I have to check on the desktop setup in those details.

If you've got a multimeter, you could check if there's a low resistance (less than a couple of ohms) from the outer case of a metal jack socket or XLR plugged into your interface, to the ground pin on a wall socket. I presume you've got Schuko sockets, so the ground pins should be easily accessible.

I'm going to try to get a hold of a multimeter, do the messurements and report. This could take a few days though.

I have trouble with a 50hz hum and the harmonic also, if there is a relation.

[Wonks]

If it happens on a desktop, when the USB connection to the interface should provide a ground reference, then it's unlikely to be a lack of ground issue.

50Hz and 100Hz hum is a common issue, just because there is so much mains electricity around. But if some of my earlier suggestion is correct and there is a possible high resistance path between the ground/sleeve connections on the interface and 0v, then the shielding could be allowing a lot more noise to be picked up than normal.

[cremedonut]

I see. I will go through this new information and do the tests as suggested. Thanks for now. I'll be back as soon as I have more information.

[cremedonut]

So I have thought about your replies and decided it would be best to buy a used interface to have a reference point. I went for a presonus Audiobox 22 VSL which is powered by USB. When it arrives I'm going to compare the 50hz (+ harmonics issue) and the crosstalk, just to make sure that the issue is exclusive to the UR242. I will let you know as soon I have further information.

[cremedonut]

Hey there,

sorry for the wait. I have now tested the presonus Audiobox 22 VSL. Input one has a guitar plugged in (the unit does not have a Hi-Z option). Input two has a Boss pedal plugged in (the pedal is not attached to anything else).

The crosstalk on this unit does only occur if I drive the Input one into clipping. Other than that there is no crosstalk visible at all. With this knowledge I come to the conclusion, that there is something wrong with the design of the UR242, my particular unit is defective or the DSP in the unit may cause this effect in a way, that I can't figure out.

At this point I am planning to buy a Motu interface.