Isolator

There are claims that sound quality improves by having a full galvanic isolation between the PC and the DAC. Some manufacturers of USB DACs use opto-couplers to eliminate the noise from the USB connection.

Exasound provided some measurements demonstrating the difference galvanic isolation can make.

 

Beware that although USB2 is supported most of the time, this doesn’t mean all the USB speed modes are supported as well. A DAC able to play > 24 bit / 96 kHz needs High-Speed (480 Mbps). A lot of isolators are limited to Full Speed.

 

As opto-couplers are used, why not use them to drive a fiber.
This gives you USB over optical hence galvanic isolation and a cable length well in excess of the 5m the USB standard allows for.
This is a technology employed by a couple of extenders.

 

Uptone Audio took matters a bit further. Their Regen is not a isolator (protecting the device against a high voltage) but a re-clocker. It re-generates the USB stream.
Their Regen generated quite a stir at various audio forums.

Uptone Audio USB REGEN US$ 175.00

 

The USB REGEN takes the digital audio stream from your computer or other music streaming device, and generates a completely new USB data signal to feed to your DAC.  It accomplishes this by combining a carefully chosen USB hub chip with an ultra low-noise regulator and low-jitter clock.  Importantly, it does so with ideal impedance matching—right at the input of your DAC.

Source: Uptone Audio

 

It regenerates the USB signal. John Swenson explains.

Added 2015

IFi micro – iUSB3.0 $399

 

According to iFI: The micro iUSB3.0 addresses all 8 significant USB audio gremlins that lead to poor quality computer audio in one fell swoop:

  • Corrects signal balance
  • Suppresses frame noise
  • Suppresses packet noise
  • Ultra clean power
  • Eliminates ground noise
  • Corrects impedance mis-match
  • Eliminates USB Jitter
  • Restores signal integrity
Added 2015

Intona High Speed USB Isolator 209 Euro/ 230 USD

  • Compliant to USB 2.0 Hi-Speed (480 MBit/s)
  • Isolation withstands 2kVRMS for 60 seconds
  • Advanced ESD protection (15kV IEC Air Discharge)
  • Backwards compatible to Full Speed and Low Speed
  • Works out of the box, no drivers needed
  • Transparent to host and device: works with all operating systems
  • Works also with hubs
  • Supports synchronous and isochronous transfers
  • Thoroughly tested with high-speed audio interfaces
  • No additional roundtrip-latency
  • Powered by USB bus, no separate power supply needed
  • Ultra-quiet power rail isolation: 100µVRMS output noise (20Hz–22kHz)
  • 250mA nominal (500mA max.) output current on isolated side
  • Connectors: host-side USB-B; device-side USB-A
  • IP 54 ABS housing
  • Dimensions: 105 x 76 x 36 mm
Added 2015
References

Digital isolator simplifies USB isolation - Mark Cantrell, Analog Devices