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In Reply to: RE: Yes, you posted one example posted by beppe61 on April 27, 2016 at 08:55:43
Ethernet USB Extenders don't necessarily offer USB Isolation properties. Good ones will. Similarly an inexpensive Ethernet USB Extender is unlikely to provide protocol translation but is probably just doing signal level conditioning. Not that protocol translation is necessary in order to achieve the benefits of isolation and signal conditioning... think Regen, Intona, etc.
USB 2 "speed" is not the issue here so you can still experiment with your entry level Ethernet USB Extender if you're willing to. Cable it up and plug in your DAC. Does it play music? Perhaps not well at hi-res rates but does it play basic 44/16 PCM? No harm in playing around with your Extenders, point to point. But if it works, that does not mean it is providing any isolation benefit.
A couple things you can try in order to determine if there's isolation between the two ends:
1) Attach the extenders to each other via Ethernet cable, but leave each USB end unattached. Now with a multimeter (ohm meter) or even a cheapie continuity tester determine if there is continuity or isolation between the two USB connector outer metal housings at each end of the extenders. Your measurement should be DC open circuit, (no connection) between the two USB connector metal housings.
An open circuit would indicate isolation properties between the two metal shield ends. This is a good start if it does in fact measure as open circuit. If there is continuity measured between the two ends, there is no isolation.
You can determine if there's isolation for each data line between each USB end by measuring from PIN 2 to PIN 2 in the same way. And between PIN 3 to PIN 3 in the same way. Measure for continuity from end to end. If it measures open circuit that's a good thing. If not, there is no isolation.
If any of the items above do not measure "open circuit", your Extenders do not offer isolation properties.
2) The other challenge is to determine if VBUS power will be passed via the Ethernet cable, or if they left it open. If these Ethernet USB Extenders are meant to be used only with USB devices that require separate (wall wart) power, they may have left VBUS disconnected.
Again, you can measure PIN 1 to PIN 1 between each USB end. And measure PIN 4 to PIN 4 between each end.
Or, attach a USB device that requires VBUS and see if it works. Attach a USB Keyboard, Mouse, small disk drive, etc. If it works, then they did in fact pass VBUSS over a couple extra Ethernet wires. You can fmak hack off the +5V line at the USB device end (or cover PIN 1 & 4) if your DAC does not require +5Vcc over USB. If it requires +5Vcc you can still hack the +5Vcc line and inject your own clean +5VDC.
Sounds like a hassle to me but if you want to experiment, the steps above should give you some insight into what your Ethernet USB Extender setup is doing.... or not doing.
Follow Ups:
Hi ! thanks a lot for the very complete and helpful directions.
Clearly i was thinking wrongly.
I thought it were a signal only cable. How sad."attach a USB device that requires VBUS and see if it works"
yes i have a dac that needs power from usb to work.
What impresses me is that much longer connections are possible with Ethernet cables than with usb.
This suggests me of an intrinsically superior design.
How can i understand if an extender provides isolation before buying it ? are they very expensive ?
Thanks a lot again.
Kind regards,
bg
Edits: 04/27/16 04/27/16
How can i understand if an extender provides isolation before buying it ? are they very expensive ?
You can't really, unless the manufacturer provides detailed features and specs for isolation. Some that target audiophiles won't even do that. And keep in mind, "Extender" does not imply "Isolation".
Unless you need to move your USB DAC a great distance from the source, an "Extender" is not necessary.
Thanks a lot again.
I tend to like rj45 link better than usb. Also the connector looks better and with the locking mechanism.
Anyway i will try out.
Thanks a lot again.
Kind regards,
bg
Edits: 04/27/16
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