Melco C1-D20 SFP+ streaming cable
Up until Melco told me about the so-called C1-D20 SFP+ direct attach cable I understood that SFP cables were exclusively optical and used glass or plastic fibre to conduct signals. Melco’s copper based C1-D20 SFP+ has revealed that this is not the case. While the SFP cables used instead of ethernet between servers and network switches are normally optical, the system supports many data transmission systems; in this case, an electrical signal via twisted cables.
SFP optical cables are driven by a PMD (physical media driver) which converts the optical signal to an electrical one. Using copper avoids this extra processing and allows the PCBs in the devices at either end to have a direct attach[ment] to one another. There are similarities with the I2S system used to transmit digital signals between a streamer and a DAC except that direct attach SFP is a standard used in IT and can be used between all devices with an SFP port. However while there is no length limit to SFP optical cables, the maximum length for SFP over metal is officially 15m, although I am told that for best results they should be limited to 9m.
In my setup, which is router > ethernet > ADOT ethernet to optical SFP converter > SFP > Melco S100 switch > SFP > Melco N1 server, the final connection has always sounded better using an optical SFP cable rather than an ethernet cable. The data carried by optical cables has to be converted to an electrical signal processing purposes and converting this sensitive data adds an unnecessary step that’s cited as a limitation for optical networking in an audio. System. Therefore, using an impedance matched direct attach cable like the C1-D20 SFP+ that doesn’t require an optical/electrical conversion stage should be beneficial, not least because it gives the data switch and receiving streamer/server an effectively intravenous connection. Melco’s Andy Moore explained that the cable needs to have an exact impedance of 100 ohms to avoid errors in the data transmission. So Melco has designed the C1-D20 to have this impedance over a 2m length.
Those familiar with optical network cables will know they have a detachable SFP module at each end, this converts the optical signal to electrical. On C1-D20 SFP+ these modules are fixed to the cable and the twin coaxial silver-plated OFC cables are screened, Melco claims the cable is immune to interference.
Although Melco C1-D20 clearly targets users of their S100/S10 switches and N5/N1 servers, the C1-D20 can be used with products from any manufacturer that uses the SFP connection, a contingent that includes Lumin, Linn, Taiko and HiFi Rose among others. So much for the theory: does the C1-D20 SFP+ produce better sounding music?
Direct attach sound
I will say first that unlike some kit that I have tested, I didn’t need to resort to repeated A/B comparisons to hear what was happening. However, I did exactly this to give you an idea of what such comparisons reveal. I have had the C1-D20 in my system for several weeks now. It arrived and was installed during a period when I had some unfamiliar review kit in the system, which was not the best time for evaluation, but it sounded better with it in, so I left it connected. I did not know the price of the C1-D20 at the time, and an official review had not been approved at this point. The price is now finalised at £749, which sounds about right for the performance benefits I experienced.
Over a weekend, I swapped back to the standard optical SFP cable I was previously using so as to make some comparisons with the Melco C1-D20. It was not hard to discern the differences between the two types of cable; going back to optical resulted in a thickening of the lower frequencies and a slightly unpleasant edge to the lead guitars of The Smile’s Under Our Pillows, from the band’s latest album, Wall Of Eyes (24/44 download). Via the C1-D20, the music sounded fuller and more organic; instruments had more detail and texture but were less bright. The latest single from the album Friend Of A Friend starts with just a bass guitar line and Tom Yorke’s vocals. Through the C1-D20, the bass guitar possessed more body and dexterity and consequently sounded more realistic. I could hear the reverb added to Tom’s vocals more clearly, and again, his vocals had more body. The piano that joins in after a few seconds sounded softer yet better resolved. As the track gets into its stride, it is joined by a string section, which now sounded far better resolved and lost the slightly unpleasant edge that was evident via the optical cable.
I have enjoyed Say She She’s album Silver many times recently, this group conjure up the spirit of late ‘70s psychedelic soul and write darn good songs to go with it. I have not got around to purchasing it yet, so was playing a 24/48 Qobuz stream. The track Astral Plane can sound a bit compressed if the system is not up to it. Returning to the optical cable resulted in the soundstage compacting and becoming more of a ‘wall of sound’, with that slight high-frequency glaze creeping in. Swapping back to the C1-D20 immediately improved things, I noticed the bass springing to life and coming further forward in the soundstage. The reverb on the guitars and the vocals was now better resolved, with both sounding more realistic as a result. Similarly, a track from the same album, C’est Si Bon, took on a rather harsh edge, and the track’s ample bass became overblown via the optical cable, meaning that I could not wait to return to the C1-D20.
One of my favourite Nick Cave songs is the track Stagger Lee from his 1995 album Murder Ballads. It only took a few bars of the intro to demonstrate the superiority of the C1-D20 here, the guitar sounding bigger but with less edge. Similarly, the keyboard strikes lost the slight harsh edge that was present with the optical connection. Nick’s vocals were cleaner, if you can ever say that about one of his pre-Boatman’s Call albums, and his spit at the end of the track’s first line had more impact. The lower noise floor revealed more studio reverb and meant I could turn up the volume higher without unpleasant harshness.
Although getting Kylie Minogue to join him on a few tracks of this album no doubt helped him to become as well-known as he is, for me, it is Polly Harvey who steals the show, especially on the track Henry Lee. I remember seeing her in Bristol at the start of her career, and it is impressive how she transformed from a screeching 21-year-old to a artist capable of the subtle brilliance of her delivery on this track. The C1-D20 makes this more obvious, revealing more texture and beauty in her voice.
Switching to some classical music from Anne-Sophie Mutter via Qobuz at 24/96, the string tone was more natural, and it was easier to hear the room’s acoustics. Violins and cellos had more body and string texture. This cable appears to work with all types of music with no downsides.
Ethernet vs metal SFP
Just as I thought I had put this review to bed, Jason suggested I should make comparisons between the SFP connection using the C1-D20 SFP+ and a comparatively priced ethernet cable between the S100 and the N1-S38. I didn’t have a £749 ethernet cable, but I found a well-thought-of cable in the drawer that costs £1,000. Thankfully, the differences were so obviously in favour of the SFP direct attach connection that this did not eat into my evening too much. The first thing I noticed was the additional air, space, definition and detail via the C1 SFP cable in place of the ethernet connection. This meant I could listen to music at lower levels without losing involvement.
A Qobuz stream of Lady Blackbird’s Blackbird in 24/44 laid these differences bare. The bass line was so much clearer via the C1-D20 SFP+ and the extra detail and air around the violin at the start of the track was immediately obvious. The extra air and space exposed her vocal ability and increased the emotional connection, which is hard to put a price on. The Say She She track Astral Plain that I referred to earlier in the review, demonstrated how the C1-D20 SFP+ opened up the soundstage and allowed the music to breathe. Like the Lady Blackbird, this track was now a far more involving listen, even at low levels. The extra information made this song sound more like a good analogue recording, smooth yet bristling with detail and with a sense of life that was missing over the ethernet connection.
Another no brainer?
If you are using a similar set-up to mine, where you have already isolated your network switch from your router and can connect your switch to a server or streamer via SFP, then the C1-D20 is a no-brainer. The C1-D20 SFP+, to use its full name, delivers music with cleaner edges and a lower noise floor. I find it amazing that products like this reveal just how much untapped performance there is in networked audio. The editor will probably disagree, but I feel confident that digital streaming systems will eventually surpass the performance of even the best turntables. If you are considering upgrading your server from one of Melco’s lower-end models or a competitor’s product, the C1-D20 demonstrates the scale of potential in purchasing something like the N5 or N1, which gives the option of using a copper SFP cable like the C1. For readers currently using SFP over optical between their switch and server/streamer, buy this cable and thank me later.