Can anyone explain USB isolators?

[Ammonite Audio]

I know that there are small USB Isolator modules available, for example from Phidgets (http://www.phidgets.com/products.php?product_id=3060), but also via eBay (http://www.ebay.co.uk/itm/OLIMEX-USB-ISO-FULL-SPEED-1000V-DC-USB-ISOLATOR-/270779403296?pt=UK_BOI_Electrical_Components_Suppl ies_ET&hash=item3f0bb5cc20). This is the Phidgets one:

http://www.phidgets.com/images/3060.jpg

Phidgets state: "The USB Isolator is designed to protect your PC from harmful voltage that can flow from devices attached to your PC through the USB cable. The isolator is inserted between the Phidgets board and your PC.

The USB Isolator can also be used to eliminate problems caused by ground “voltage” differences between USB Host and USB devices."

The eBay seller further states that "Isolators can be useful in low noise audio environments to eliminate ground loops."

It seems logical to use such a device between the (presumably) noisy USB bus of the host music server PC, and the DAC or, in my case, the HiFace Evo asynchronous USB converter, in order to minimise any negative effect of the PC. Is it logical to assume such a thing? If anyone can explain how these isolators work, particularly with an eye on audio applications, I'd be very grateful.

[Mark Grant]

A link:

http://www.analog.com/library/analogdialogue/archives/43-06/USB_isolator.html

Some of the devices convert the electrical signal to optical then transmit the optical signal across a very small gap to an optical receiver then convert it back to an electrical signal, so that there is no direct electrical connection of the USB data.

Others use very small transformers for the signal to 'jump' across the windings.

Its not always clear which devices fully isolate the power connections.

That's the short, non technical answer.:)

Worth a try although ideally buy from somewhere in the UK that accepts returns.

link to one I have seen mentioned:
http://electronics-shop.dk/?id=1038&currency=EUR&pollanswer=1

google image search might find a few other makes:
http://www.google.co.uk/search?q=usb+isolator&hl=en&prmd=ivnsfd&tbas=0&bav=on.2,or.r_gc.r_pw.&biw=1503&bih=1003&wrapid=tlif131210177599010&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi

A link with some comments:
http://www.computeraudiophile.com/content/Acromag-USB-Isolator-simple-and-inexpensive-bus-powered-USB-isolation-ADuM4160

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[Vincent Kars]

Probably a bit more than you wish to know: http://www.analog.com/library/analogdialogue/archives/43-06/USB_isolator.pdf

If you buy, check if high speed mode is supported.
This is probably needed by the Evo.

DACs like the Ayre QB9 comes with a galvanic isolation between DAC and USB receiver.
The idea is that the USB power lines might contains stray signals disturbing the DAC.

USB receivers like the XMOS have opto couplers.
Basically a USB to Toslink converter
http://thewelltemperedcomputer.com/HW/USB_Interface.htm

[Maximum]

If the Evo is like the standard Hiface then it should have galvanic isolation in the box. If you find your sound a bit forward you could try jkennys suggestion of an attenuator on the spdif, it seems the calm the slight forwardness of the hiface a bit, although they might have lowered the output for the Evo version.

[roob]

From M2techs website re Evo

All outputs, except straight I2S, are galvanically isolated (coax and AES/EBU via a pulse transformer).

[Ammonite Audio]

Andy, I wasn't aware that the Evo has that galvanic isolation. Nevertheless, I'm still tempted to add one of these to my new music server PC build, since two levels of isolation may be better than one!

[sq225917]

The Evo and the Young both shares the same isolation.

[technobear]

I use the one from electronics-shop.dk

Without it I can here PC noises coming through my speakers (when no music is playing). That is disturbing my inky black background. Tsk! :steam:

With the isolator, perfect silence http://www.technobear.btinternet.co.uk/emoticons/stereo.gif

[sq225917]

TB, that's crazy poor USB isolation on the CDQ then...

[technobear]

TB, that's crazy poor USB isolation on the CDQ then...

Not so much poor as there is none. They didn't put it in.