• Registered: 2011-04-05
  • Posts: 17

Topic: USB Isolator (High-Speed mode)

Dear all,

I'm experiencing noise issues, when running the FF UC from my Laptop with the Laptop connected to the mains supply. The noise is completely absent when using the Laptop battery.
--> Sounds like an USB Isolator should solve the problem.
BUT: So far I have only found USB Isolators being "USB 2.0 compliant". All of them support 1.5Mbit/s and 12Mbit/s mode but not the High-speed mode with 480Mbit/s.

Questions:
- Will the FF UC run with USB 1.1 speed? (simultaneous 2-Ch in / 2-Ch out @ 24bit, 96kS/s (192kS/s))?
- Does anyone know a USB isolator featuring "full-speed" mode?
- Does anyone know if this is not feasible from a technical point of view (latency, etc.)?
   (I'm wondering, why there's no chipset available supporting "full-speed" USB 2.0 ...)

Sounds like a topic that might have been covered already, yet I did not find a thread while searching. Apologies if I missed one.

Thank you very much
Best Regards
Mathias

2 Reply by MC

  • MC
  • MC
  • Administrator
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  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 24,847

Re: USB Isolator (High-Speed mode)

That will not work. The more easy way is to isolate ground from the 3-prong plug by an additional mains transformer (230 V to 230 V). Searching this forum or the web you will also find another very simple way...

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2011-04-05
  • Posts: 17

Re: USB Isolator (High-Speed mode)

Thank's a lot for the immediate answer (especially since it's easter holidays, strictly speaking...).

It's indeed the classic "ground-loop". I did not at all expect the secondary (DC) side of the SMPS to be connected to protective earth, but it is.
--> I might resort to the classical very simple way ....   ;-)

Anyway, if someone knows an affordable USB-Isolator that works at USB2.0 "high-speed" mode, I will be happy to hear about.
There are guys who claim to be able to build one, but this one looks rather unaffordable ...
http://www.baaske-medical.de/product_in … 24-EU.html

Regards
Mathias

  • Registered: 2007-05-09
  • Posts: 23

Re: USB Isolator (High-Speed mode)

Polarbear wrote:

It's indeed the classic "ground-loop". I did not at all expect the secondary (DC) side of the SMPS to be connected to protective earth, but it is.
--> I might resort to the classical very simple way ....   ;-)

Don't fixate on this USB isolator. If your laptop has a 3-pin mains plug, just try first to isolate its ground by means of a short adapter cable:  3-hole female contraplug  => 2-pin male plug. That took 5 min to build, cured my FF400 issues and hasn't killed me yet  :-)

  • Registered: 2011-04-05
  • Posts: 17

Re: USB Isolator (High-Speed mode)

@Tom: Thanks for sharing the good experience.
My Laptop adapter indeed has 3 terminals and it connects the Laptop ground to the protective earth (as does my amplifier).
I have just started to built an adaptor cable that separates the protective earth for voltage differences of up to +/-6Volts and gets conducting for voltage differences beyond this. This should normally suffice to remove the ground-loop issue and should still keep the Laptop Ground from floating too far away such that there is a risk to damage e.g. the USB port when plugging it in.

Still this is a measure that is NOT safe and it violates fundamental safety regulations.
THEREFORE I WANT TO EXPLICITLY WARN PEOPLE: DO NOT COPY THIS WORKAROUND! IT'S COMPLETELY AT YOUR OWN RISK!