Intro
Contents
Every link in the hi-fi chain counts. Energy, sources, acoustics, the rack, the ears … and…the network. We’ll take a look at a few different solutions. Including single mode and multi mode fiber optics.
In the 21st century, streaming has become the most common way to listen to music, this is true even for hi-fi enthusiasts. Listening to the market around me, the general opinion is that it may be a little easier to achieve good sound quality with CD or vinyl, but the convenience of streaming and the huge selection available through streaming services often wins out.
Streaming does require a bit more effort to achieve the same quality as CD, for example, there are many factors within the digital circuit that can affect the quality of the final analog signal. In this review we are going to highlight one of them: the network connection, and specifically the wired one.
Bluetooth is a possibility, but because a Bluetooth receiver itself generates a lot of noise, it is not the most obvious choice for good quality. Add loads of compression and you get the point.
Noise level
In a network for high fidelity streaming, basically everything is aimed at keeping electrical noise, which unintentionally and inevitably travels along with the electrical square wave of ones and zeros, as low as possible. After all, noise can affect the clock of the streamer or the DAC, resulting in jitter. There are several ways to bring this noise level down, the simplest being a passive filter with a good RJ45 cable from the filter to the streamer. Another option is a high quality switch and from there again a good cable to your streamer. You can improve the switch with a linear power supply and if the switch and streamer allow it, you can create a galvanic connection with fiberglass.
SFP connection and fiber optics
SFP stands for Small Form-factor Pluggable, the connection is designed to make switches flexible. There are both copper and fiber versions of SFP modules. And they come in a variety of speeds.
Pluggable means you can plug in the module (if the switch has a slot for it). And – depending on the module – various cable types are possible: singlemode fiber, multimode fiber, copper (UTP, FTP, S/FTP) and also, for example, direct attach copper (DAC for short, yes indeed confusing).
As we know, fiberglass is very popular because it can transmit a lot of data quickly, and has high reliability and stability. The advantage for us audiophiles is that the data are transmitted with light, giving you galvanic separation and (virtually) no electrical noise.
Multimode versus Singlemode fiber optics
So what are the differences between multimode and singlemode fiber optics? Multimode has a larger core, 50 or 62.5 µm, light passes through the fiber via multiple paths and uses an LED as a light source. Multimode is cheaper than singlemode and is generally used for shorter distances, less than 500 meters. Singlemode has a smaller core of ~9 µm and the light passes through the fiber via 1 path straight through and has a laser as the light source. It is more expensive than multimode but can cover up to tens of kilometers of distance. Singlemode is theoretically the recommended option for us audiophiles, multimode does also create galvanic separation, but because singlemode has a smaller diameter there is less interaction of the light with the wall of the fiber and this leads to less “pulse edge jitter.”
Transceivers
If you work with fiber you always use SFP transceivers, these are the modules that convert electricity to light and vice versa, quite impressive for those little things. You plug the transceivers into the SFP connector of the switch, for example, and at the back you insert the fiber optic cables, there are always two, one for outgoing data and one for return. The transceivers are specific for singlemode or multimode and therefore not interchangeable.
I can imagine that these SFP transceivers may still affect the audio quality, but there is remarkably little information on that on the Internet, zero reviews found and thus seems to be some unexplored territory. The singlemode set we are testing here from Adott are, according to the manufacturer, specially selected for audio purposes but that’s about it.
Direct Attach Copper
If you can choose galvanic separation, why would you still choose a DAC cable? Well, the theory is this: with fiber optics, you will first have to convert the data from electrical to light and then from light to electrical again, and you might prefer not to have these conversions sitting right in front of your streamer. A DAC cable connection is less complex, less chance of interference, disadvantage is that it’s not galvanic separation, you’ll have to bring down the noise level some other way.