• Registered: 2021-03-12
  • Posts: 71

Topic: UCX II + ARC USB long wire

I have used ARC USB connected directly to UCX II with my old 5 m shielded extension cable and ARC cable from the box.

1. In ARC USB documentation is written:
Non-critical USB 1.1 connection allows to use long cables
What does it mean "long cables"? How long connected to PC and how long connected to standalone UCX II?

2. During last month happened twice that UCX II seemed like restarted.
Several time ARC was not responsive and I had to disconnect it and connect again. Then it was ok for long time. Something like this https://forum.rme-audio.de/viewtopic.php?pid=191943

3. I noticed that when ARC is connected and UCX II switched on - very strong constant RF interference is emmited  from ARC or cable. When I connected flash disk via the same extension cable - there was no interference. When I replaced stock USB cable from RME with better cable it was the same. I noticed it with my CB station operating around 27MHz, reception was impossible. No other USB device does this, only some poor quality mobile phone switching chargers.

4. I wanted to replace those 2 USB cables with one a bit longer, it was just a provisorium. So I bought 10m "printer" cable expecting good performance because of less connectors. But ARC started to switched on/off in a cycle.
I bought another cable with usb2 repeater after 5m. When I connected it to UCX II, there was no voltage on cable output, everything was taken by the repeater only. When I connected ARC via both cables to PC - everything worked perfectly.
But not with UCX II.

My opinion is that UCX II usb is not able to deliver enough current without dropping voltage too much, big internal resistence.
USB2 should keep 5V/500mA according standards.
UCX has 5.1V unconnected. BUT when you connect ARC, current is much higher for a short time and voltage on cable drops to 4.8V. Once it is stable ARC has consuption around 20mA according my measurements with this very small current voltage drops from 5.1V to 5.0V.
That is probably the reason why with long cable it cycled - switched on, voltage dropped, off, voltage raised, on, dropped...
Seems like UCX USB implementation doesnot keep USB2 standard.

Or ARC should have something like soft start not to take so much current in the beginning.

And because I need standalone use (this and long cable allowed were among main reasons why I bought both) I am a bit dissatified with otherwise very good gear. I have spent many hours and money trying to solve unsuccesfully.

Is there any possibility to solve this? Allow bigger current via change in firmware or something else? I really don't want to have shorter USB cable across my room.

ADI-2 DAC, Digiface USB, Fireface UCXII, ARC USB, Neumann MA1 aligned monitors
  • Registered: 2021-03-12
  • Posts: 71

Re: UCX II + ARC USB long wire

I would like to ask if this behavior is standard for UCX2 and ARC or if there is any of those devices bad and I should take replacement from the dealer. It is still under warranty.

ADI-2 DAC, Digiface USB, Fireface UCXII, ARC USB, Neumann MA1 aligned monitors

3 Reply by MC

  • MC
  • MC
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  • Registered: 2007-04-06
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Re: UCX II + ARC USB long wire

The ARC USB is not critical and also runs at lower voltages. While the UCX II output does not have to follow 'USB standard' (this is not a universal USB host nor a motherboard), it still provides 0.75 A at a voltage of 4.86 V - which fits the 'standard' well.

IMHO the most easy solution here is to get one of those special 'double power' USB cable splitters, like we had shipped with the first generation Babyface. You can then feed 5V directly at the ARC USB. The UCX II includes a reverse protection diode, so current won't flow back to the unit.

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2021-03-12
  • Posts: 71

Re: UCX II + ARC USB long wire

Thank you for answer.
Yes, this can be some workaround. But it needs some other power source which will feed ARC permanently or will need separate power switch and so on... not ideal.
Maybe better to have some adapter between UCX2 and its power source and use stepdown module 12V to 5V USB, it can handle up to 2A, but still ARC will be permanently powered. Maybe, I don't know how the power source would react.

Currently it works with 5m usb extension and 3m better thicker printer cable - together 8m. But I would need 10m, just 2m more, to hide cable behind furniture. Maybe I will try to find some better cable.

Each time I sit in a sofa having ARC on left hand I see how great device it is comparing IR remote control, my adi2 dac IR remote buttons for volume stopped responding after some months. Maybe I pressed too much. :-)

ADI-2 DAC, Digiface USB, Fireface UCXII, ARC USB, Neumann MA1 aligned monitors

5 Reply by MC

  • MC
  • MC
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Re: UCX II + ARC USB long wire

Replace the battery...

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2021-03-12
  • Posts: 71

Re: UCX II + ARC USB long wire

It is not battery, it is bad contact only on volume Up/Down buttons which I used very often, other buttons work well even after two years.

ADI-2 DAC, Digiface USB, Fireface UCXII, ARC USB, Neumann MA1 aligned monitors

7 Reply by MC

  • MC
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Re: UCX II + ARC USB long wire

Contact your local distributor, they might be able to exchange the remote.

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2021-03-12
  • Posts: 71

Re: UCX II + ARC USB long wire

Now it is 3 months after end of 2 year warranty. I already bought universal 4-device IR remote and programmed it. It is much more robust and reliable even after more than 1 year of use. If it will break after some years, I can clean it inside as any other bigger one before and it will work again or I will buy another one for 12 EUR.
My remotes have often problems with volume buttons after years because they are used most often, maybe my bad use. But never after such a short time.

ADI-2 DAC, Digiface USB, Fireface UCXII, ARC USB, Neumann MA1 aligned monitors