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In Reply to: RE: Usb extenders instead that normal usb cable ? posted by beppe61 on July 31, 2016 at 10:51:41
I understand that these extenders provide galvanic isolationAre you sure they do?
Using a CAT5/6/7/ cable doesn't say it is Ethernet hence adhere to the Ethernet standard and provide galvanic isolation.
They don't claim you can use it in your LAN
Probably not an Ethernet solution
The Well Tempered Computer
Edits: 08/01/16Follow Ups:
" Using a CAT5/6/7/ cable doesn't say it is Ethernet hence adhere to the Ethernet standard"
As far as I am aware all Ethernet cables are Cat5/5e/6/6a/7 and,as the Cats describe standards, vice versa. The standards relate to maximum bandwidth, transfer speeds and testing. The basic requirements for digital audio use are met or exceeded by all although the higher numbers reflect in part better interference rejection which may or may not be an issue in given circumstances.
Correct but I'm afraid the question is not about band width.
OP wants galvanic isolation.You have a sender and a receiver connected with a CatX cable.
Does this provide galvanic isolation between the two devices?
Obvious a cable certainly doesn't.If the protocol between the two devices is Ethernet then we expect galvanic isolation on the data lines as this is the requirement of the Ethernet standard.
If not there might be a galvanic connection.
They simply use CatX because of convenience / price /able to use a balanced connection/ whatever.A simple "test" is can you use the extenders over a LAN.
If you can it most be Ethernet.
If you can't it is probably not Ethernet.
The Well Tempered Computer
Edits: 08/01/16
Hi again,
from what I have read galvanic isolation between pc and usb converter/dac is a very good thing to have.
I understand now that these cheap units hardly provide a proper electrical isolation from the pc.
However, tempted by the very low cost I bought one set to try out.
I did some test with an even cheaper product in the past.
This will sound strange.
Between the clicks/drop-outs( the extender was not able to sustain even a 16/44 bitstream) I heard something promising. Like a lower noise floor.
This set should pass 480 Mbps without clicks.
I do not know anything about isolation.
Still i am very curious to listen.
Kind regards,
bg
Edits: 08/01/16 08/01/16
fmak hates it when I post pictures!The original intent:
Ethernet can support long runs such that equipment on different ends can be powered from distant branches of the AC power distribution system within a building or across different buildings.This means there can be significant ground offset between Ethernet devices. The Ethernet coupling transformers mitigate these ground offsets and provides galvanic isolation.
The transformers also provide for common mode noise rejection as well as relatively high voltage isolation between the primary and secondary sides of the transformer.
Simplified Schematic Example
The small transformers can be separate devices on the PCB or built into the RJ45 Ethernet jack itself.
If your low-cost USB / Ethernet extender device does not use some sort of transformer (magnetic coupling) or optical coupling you will not achieve the benefit of galvanic isolation. One way to tell w/o breaking into the device is to use a DMM to measure for DC continuity from the input to output end of the device. Transformers are meant to pass AC. You do NOT want DC continuity between each end.
Example Ethernet transformers
Example RJ45 jacks with built-in transformers
Edits: 08/01/16
Hi ! sorry to disturb you again.
In case the extender ports will not be transformer-coupled, are you aware of RJ-45 adapters (male to female) with transformers inside ?
That would solve the issue.
Thanks a lot again for the very valuable advice.
Have a nice day !
Kind regards,
bg
Edits: 08/02/16
transformer coupling a signal pair isolates but can be at the expense of signal integrity. There are issues of transformer quality as well as ground bounce and lack of symmetry.
IT guys talk about 'isolation' in isolation as though this is a magic fix. Well, it ain't, as those with electronics know-how will know.
Hi !
thanks for the valuable advice.
I think I see your point. Transformers really have and effect on signal.
Giving the good reviews of some lan streamers like the microRendu I guess it is an issue of build quality ?
However ... i will do a simple experiment. I will use this extender without the accompaining psu.
If the usb dac will not work it means that it does not receive electrical power from the pc. So is at least electrically isolated.
I have to see inside and I will post some pictures to get advice.
I do not know if the sender takes power from the pc by the way.
I am quite sure that the receiver has its own psu.
Thanks a lot again.
Kind regards,
bg
Was that your contribution for the day? Helpful as usual, I see.
Edits: 08/02/16
I don't know if they exist. I have never had the need to investigate because Ethernet devices that are truly compliant will already be galvanically isolated w/o the need for inline transformers.
Hi ! thanks a lot indeed.
I will open them and see inside.
I really hope it will be the case.
Kind regards,
bg
Hi !
thanks a lot for the very valuable advice.
Asa i will receive them i will open and see. I am crossing fingers.
Actually they are not exactly cheap on the catalog.
I am very curious to listen.
At present i am using only a cheap isolator with Audum chip.
Kind regards,
bg
I think this unit is totally new and yet unproven, but seems to me the cheapest box that may offer satisfactory isolation of USB for music playback purposes.
http://www.alldaq.com/en/adq-iso
Hi !
thanks a lot for the interesting advice.
I am using a very cheap one, the one in the link
A similar chip is used also in some usb to spdif converters of good level.
I believe a lot in isolation from the pc power.
Kind regards,
bg
Hi !
no i am not sure 100% about the galvanic isolation but i see that the receiver is externally powered. The sender instead takes power from the usb bus in the pc.
I have only one main system that i care of.
So the Lan functionality is not a requirement.
At present i am using a cheap usb isolator based on Analog Devices Adum chip.
Kind regards,
bg
Edits: 07/31/16
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