I’m posting a major tweak that hugely improves the sound quality of the streamed sound.
It’s about FMCs that convert the DATA carried by USB packets to optical, and then back to electrical, in order to remove the electrical noise that will penetrate otherwise into the DAC. These converters work with SFP modules and fiber, the same way the FMCs that we are using to remove the noise from the Ethernet packets that we stream to the endpoint.
Last year, I noticed the existence of a such device, named Nocturnes, on the site of AfterDark. It’s pricey, and I could not find any feedback about it.
A few weeks ago, @FrankLeRouge told me on Forum hifi, a French language forum, that he uses USB optical converters between his streamer and his DDC that is connected to his DAC by I2S. (Franck is a passionate audiophile, and an electronician who built many audio devices over 35 years. This is a link to a picture of his listening room in which he built by himself all the devices of his 9 channel speakers system:
http://forum-hifi.fr/attachment.php?aid=1785 )
Franck gave me the link of the Ali shop from which he bought his USB converters. He warned me not to buy any other model on Ali, neither cheaper nor pricier. The model that he uses being the only one that he tried, and can confirm that it works well. It has an OCXO clock on the receiver side.
I ordered the USB converters, and they cost me €317, including the shipping by Fedex. It’s about 25% of the price of Nocturnes, and its additional costs of shipping and custom fees.
https://fr.aliexpress.com/item/1005...t_main.41.21ef5e5bsYeIdz&gatewayAdapt=glo2fra
I received the converters last week.
How To Make Them Work
The transmitter should connect to the USB output of the streamer, which also powers it with 5 V through this port.
For the receiver, a good LPS with an output between 7.5 V to 10 V is necessary. I power mine with the 9 V output of a Keces P8.
The converters come with a blue fiber, and SFP modules from Nokia that do not sound good. They kill the sound.
I’m using mine with the Finisar SFP 1475 modules, with whom I get the best results. The Finisar AOC cable, also performs well.
I made many tests with these converters, I’ll report just a few.
LAN input of the Gustard R26 versus its USB and I2S ports (with the optical isolation)
My DAC, the Gustard R26, has a good built-in streamer that I don’t usually use. I get a more refined sound with my Rpi based external streamers, running GentooPlayer, and the Diretta streaming protocol.
Before receiving the USB optical isolation, I was getting the best results with the Holo Red, configured as a streamer, and its I2S output.
The Red is a versatile device that can be used both as a streamer (USB or I2S), and as a DDC.
The addition of the USB optical isolation to my streaming setup enhanced amazingly its sound quality, and changed the way that I’m using the Red.
I tested the USB isolation with my Allo USBridge Sig, streaming with Roon in bit-perfect mode.
On the Allo, I run RopieeeXL in order to hear the effect of the USB optical isolation without any improvement that GentooPlayer and Diretta might bring.
The setup was like this:
a. Mac Mini M1 > RAAT > R26
b. Mac Mini M1 > RAAT > Allo USBridge (RopieeeXL) > USB Optical isolation > USB > R26
With the optical isolation, the sound streamed to the USB port of the DAC was incredibly better. In the A/B comparisons, it was day and night, and I could clearly hear digital artifacts with the LAN input of the R26.
The difference perceived in sound quality was due to the higher level of noise reaching the DAC circuity with the built-in streamer of the R26.
Then I added the Red to the loop. To benefit from the USB optical isolation, I configured the Red as a DDC. The setup was like this:
Mac Mini M1 > RAAT > Allo USBridge Sig (RopieeeXL) > optical isolation > Red (configured as a DDC) > I2S > R26
The sound was improved again. It was clearly the best sound that I ever heard on my system! Much better than using the Red as a streamer.
The Red is just a more silent device when it is used as a DDC rather than a streamer that runs an OS, and processes the tracks.
I proceeded with the same tests with my Audio-GD DI-20HE. With it, the sound was of a similar grade of quality.
My Present Streaming Setup
The sound with GentooPlayer and Diretta remains more refined than with RopieeeXL, but as the optical isolation suppresses completely the noise of the streamer, the difference is small.
At the present, the USB optical isolation is fully integrated to my system in the following setup:
NUC (GentooPlayer, Diretta Host) > Diretta > Allo USBridge Sig (Diretta Target) > USB optical isolation > Holo Red > I2S > R26