I was reading the A’gon thread about the "Stereo Times Most Wanted Components" and saw that a digital isolation device had made the list (Aardvark Ethernet Isolator). I did a shallow dive into these isolation devices and found out that network isolators are typically electromagnetic voltage transformer modules that provide electrical isolation, improve signal integrity, and minimize electromagnetic interference (EMI). The module itself appears to cost around $10.
In addition to the StackAudio SmoothLAN Network Filter ($250) discussed in this thread, solutions that seem similar include:
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English Electric EE1 Network Isolator, for $295,
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Crux Audio LAN Noise Filter, currently priced at $250,
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Aardvark Ethernet Isolator, for $450 or $900,
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CAD Ethernet Control, for $1,250,
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EverStar MI-300 Ethernet Galvanic Isolator, for $87, and
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emo System’s EMOSAFE EN-70HD, for $172
I have no idea what would make one device actually sound better than the others, especially since they all seem to be based on a filter module costing around $10, but audio reviewer Roy Gregory apparently discerned a difference between three of them and wrote about it in this article at Gy8, where he (predictably?) explains that the performance gets better as the price goes up, from the English Electric EE1 (good) to the Aardvark Ethernet Isolator (better) to the CAD’s Ethernet Control (best). Setting aside the perceived hierarchy, I am curious how the improvements can be so precisely graded for a product category that many believe provides subtle differences/improvements, if any.
Looking into the non-audio system related uses (i.e., industrial and medical networking) I learned that, at least in the case of medical applications, Ethernet isolators should conform to the requirements of IEC 60601-1 for galvanic isolation devices in the medical field.
This made me curious whether most/all component devices that interface with an RJ-45 Ethernet cable already include transformer isolation so I found this:
A typical Ethernet port includes isolation transformers, common mode chokes and port termination as shown in Figure 1. The transformers have a minimum isolation rating of 1500 VRMS (2.1kV) as required by the IEEE 802.3 standard for Ethernet interfaces. Common mode chokes are often integrated with the isolation transformers and serve to reduce EMI emissions. Ethernet ports are commonly terminated using the “Bob Smith” technique. This termination uses a 75 Ohm resistor for a common mode impedance match at each signal pair, collectively connected via a high voltage 1000pF capacitor to chassis ground. The purpose of this termination is a further reduction in common mode emissions.
Figure 1 – Ethernet Interface Components © Semtech Corporation 2020
Maybe somebody more familiar with Network related devices can explain whether this type of isolation is typical for Ethernet endpoint ports in devices such as switches and streamers and, if so, why do we need an additional in-line device? IOW, are these commercial "audiophile" filter devices fixing a problem not in evidence and, also, what is so different about them that they can affect the sound to the extent as reported by the reviewers and end users?
