It has been clear to me for some time that the interruption of LAN cables by optical fibres and media converters in digital playback systems can bring significant sonic advantages. How much more euphony one can hope for also depends on the quality of the converters. For this reason the Audiophile Grade Optical Fibre Kit was a discovery for me.

Already during the first examination of the Fibre Kit, it became clear that the set consisting of a media converter and its own linear(!) plug-in power supply has a little more to offer than a combination of the usual converter for IT applications plus a high-quality power supply, regardless of whether it comes from SBooster or Keces. With one of these two power supply units, the Fibre Kit sounds even better. I was already able to gain these impressions with a single ADOT converter, because the second one has been stranded in a UPS warehouse for a month on its way from England to Gröbenzell. In the meantime, Mika Dauphin, the head of Drei H Vertriebs Ltd, who distributes Audiophile Digital Optical Technology products in Germany, has sent me another audiophile media converter.

But before I loop the second ADOT in my system, I would like to briefly discuss the various applications for fibre optic cables. The technology was developed to be able to transmit electrical signals, such as those of Ethernet connections, over very long distances without loss - depending on the SFP adapters and suitable fibre optic cable, up to 100 kilometres should be possible. Not necessarily what music lovers need in their homes. When streaming locally stored music files, however, it has also been shown that the complete galvanic isolation of the audio components from the Internet benefits the playback quality. One possibility, of course, would be to rigorously dispense with a connection to the Internet and thus to streaming portals such as Qobuz or Tidal and to set up a separate network just for digital music reproduction. This is exactly what I did in my listening room. But thanks to galvanic isolation through simple media converters with selected SFP adapters, high-quality power supplies and audiophile Lan cables between the converters and the router or Lan switch, I can now access streaming services without compromising the playback quality of locally stored files. In my setup, a fibre optic cable of 20 metres overcomes the distance between the two converters, as the router is located in a different room than my system for good reasons. The duplex single-mode conductor thus bridges a distance that is considerable for electrical conductors, but negligible for optical conductors, and ensures complete galvanic isolation between the Internet and the network that the switch, the NAS and the streaming bridge form.

With the ADOT Kit, the focus is on galvanic isolation, and the data regeneration as above : in addition to the converter, it consists of two SFP adapters, the matching duplex multimode fibre optic cable of 1.5 metre length and the linear plug-in power supply already mentioned. If you add a switch with a built-in media converter like the Melco S100 - or also the SOtM sNH-10G - you can easily isolate the digital audio components from the internet and still be connected to it. The fact that ADOT probably first sees owners of Melco switches as a target group does not mean that users of other switches are neglected. In addition to the Fibre Kit, they also need the MC Accessory, a box with another ADOT media converter, a Y-cable for the power supply and a Melco C1AE Ethernet cable. If galvanic isolation is the primary concern, this combination is also logical: the LAN cable, which previously connected router and switch, for example, is plugged into the first media converter, then it continues via fibre optic cable and the Melco cable is used between the second converter and the switch. Since the linear plug-in power supply is strong enough to feed two media converters, the Y-cable is used to connect the two. However, its length - or shortness - suggests that ADOT does not expect to bridge a distance of 1.5 metres with the fibre optic cable. For all users who already operate an optical fibre link with selected SFP adapters and high-quality power supplies, it would be nice if they could purchase the ADOT converters without accessories. But you can talk to the sales department or the dealer of your choice...

Since in my system - as I said - Ethernet data have also been transmitted optically for some time, I currently use only the two ADOT modules. I cannot explain why, during the first test with the Melco switch, the transmission only worked when I no longer limited the transmission rate to 100 megabits via the DIP switches, contrary to the ADOT recommendations. I have now activated the bandwidth limitation declared as audiophile for both converters and the data transmission works without problems. But according to my experiences so far, a little break-in time is now called for for the media converters, which they complete in the background while an immensely exciting phono stage collects operating hours.

The play-in phase has the advantage that I switch from the - as I firmly assume - better configuration to the slightly less good one during the following comparison. And experience shows that the way back is always the more difficult - or easier, when it comes to recognising changes. This is no different here. Whereas before I was sure that I had never heard the two or three test pieces so well through my system - to which, apart from the ADOT converters, the modifications to the Melco NAS certainly contributed - the switch back to the two 10Gtek made the sound stage shrink a little. The reproduction had lost some of its smoothness, and the high frequency range seemed minimally hardened. The differences were not huge, but clearly perceptible over a high-resolution chain. In the high-end range, it's these little things that make the difference.

When I then looped in the ADOTs again - the whole change took less than two minutes - the sonic advantages of the higher-quality converters seemed greater to me than in the first comparison: Keith Jarrett in his trio now seems to have much more fun with the old standard "God Bless The Child". The three groove even more intensely. The spatial imaging has also improved thanks to the ADOTs: The instruments now seem more three-dimensional on the larger stage. Here and there, you can also hear a little more detail. Keith Jarrett is one of those musicians who are not really quiet. The spectrum ranges from audible breathing and rhythmic foot movements to stomping and humming along to the melody. Thanks to the ADOTs, you can participate in all of this. There is no need for further comparison: In my system, I would no longer want to do without the ADOT media converters.

I'd rather hear whether the media converter in the Melco switch differs from an external ADOT. The router is connected to the one ADOT via an Audioquest Diamond. The fibre optic cable leads to the slot of the Melco S100, which contains a Finisar SFP adapter. As with the first attempt with the ADOT converter and the Melco switch, I don't hear anything at first. But now I know what the problem is. The Melco Switch does not like a bandwidth limit of 100 megabits with the ADOT. So I switch it off with the two DIP switches and restart the converter. By the way, the cabling to the Melco NAS and to the Aries G2.1 - and later also to the external media converter - is done by the Ansuz Digitalz D-TC Supreme, which gets its low-frequency AC voltage from the Ansuz PowerSwitch. The S100 is allowed to warm up for an hour with Jonas Hellborg and Glen Velez' "Ritual Love-Death" from the album Ars Moriende, a unique indulgence of percussion and bass guitar sounds, respectively imaginary space and impulses. An audiophile delight!

As beautiful as the files are, for the comparison between the internal and external converter I prefer to rely on one of the excellently recorded albums of the Living Concert Series: Shostakovich's Symphony No. 15. The recording with its abundance of spatial information clearly benefits from the second media converter - and the bandwidth limitation to 100 megabits? In any case, the stage seems a touch deeper and the rhythmic reproduction is a little more intense. The media converter built into the Melco is very good, the external one even a little better. Owners of the Melco S100 can thus reach the highest sound level in small steps.

Finally, the media converter integrated into the SotM switch also has to compete with the ADOT: Again, I start with the internal converter, after having enjoyed Jonas Hellborg's acoustic spectacle also via the SOtMs - the switch sNH-10G, the clock sCLK-OCX10 and the clock cable dBCL-BNC. This time I chose the Paul Motian Trio's "Folk Song For Rosie" from the album Le Voyage as the test file: Here the difference between the converters is even greater than with the Melco. With the internal one, the sound is not very homogeneous: The saxophone plays in a rather reverberant environment, the drums in a different room, and the bass was miked very close. With the ADOT converter, on the other hand, you can hear that especially during loud saxophone passages, the sound also spills over to the right, where the double bass seems to be. The spatial arrangement of the instruments seems more realistic, the strongly picked strings of the double bass have more energy, the hits on the cymbals are even more differentiated, and the saxophone comes with bite but without aggressiveness: simply great!