Fidelity Imports
Matrix Audio SI-1 Network Isolator | TweekGeek
Matrix Audio SI-1
Network noise is real and it is audible. The Ethernet cable connecting your streamer to your router or switch carries data, but it also carries common-mode interference — electromagnetic noise generated by switching power supplies, ground potential differences between devices, and the high-frequency hash that modern network infrastructure radiates. None of this belongs in a signal path. The SI-1 is Matrix Audio's answer to that problem: an active optical-electrical isolator that sits between your network switch and your streamer and removes the electrical connection between them entirely.
It is a small box. What happens inside it is not simple.
How it works
The SI-1 uses a dual-channel optical transmission architecture — separate optical paths for transmit and receive. The incoming Ethernet signal is converted to optical, transmitted across an electrically isolated gap, and converted back to electrical at the output. No electrons pass between the input and output ports. Ground loops cannot form. Common-mode noise from the upstream network has no path to the downstream audio equipment.
The output port also incorporates a physical electrical isolation washer at the RJ45 connector, adding a further layer of separation. The result is that the SI-1 does not merely attenuate noise — it breaks the electrical continuity between the network infrastructure and the audio component completely. Lightning, power surges, and electrostatic discharge from the network side cannot reach the streamer or DAC on the other side.
Clocks and power supply
Optical isolation introduces a reclocking requirement — the signal has to be regenerated on the output side, and the quality of that regeneration depends on the clock used. The SI-1 uses two femtosecond clocks, one for each transmission direction. A linear power supply built around a dual-winding potted toroidal transformer and multiple LDOs powers the device, with the dual windings providing independent supply rails for the two clock and transmission circuits. The approach is consistent with what Matrix has applied across the N Series and M Series — linear power, multiple LDOs, and the best available clock hardware for the task. In a network isolator, this is not common.
What it does to the sound
The effect of effective network isolation is a lower noise floor — what is often described as a blacker background. With less noise corrupting the signal arriving at the streamer's input, fine detail that was previously masked becomes audible. Spatial information improves. The improvement is more obvious in some systems than others, typically more significant where the network infrastructure is noisier or where the rest of the system is already well resolved. In a system built around the NT-1, MS-1, or MS-1c, the SI-1 is the upstream problem the rest of the chain cannot solve on its own.
Practical details
Two 1Gbps RJ45 ports — one input from the network switch or router, one isolated output to the audio component. Full gigabit throughput is maintained; there is no bandwidth penalty for the isolation. The LED indicators on the rear Ethernet ports can be switched off, which Matrix includes for a specific reason: in a darkened listening room, activity LEDs blinking in your peripheral vision are a distraction. The front panel LEDs show power and link status clearly when needed and can be left on without issue.
The enclosure is CNC-machined aluminium in unibody construction — the same design language as the rest of the Matrix N and M Series. At 120mm wide it sits unobtrusively in a rack or on a shelf. At 1.54kg it is not going to move. The power supply is factory-fixed voltage — confirm the US configuration with us before ordering.
Where it fits
The SI-1 connects between your last network switch and the Ethernet input of your Matrix streamer — or any other network audio device with a 1Gbps RJ45 input. In an N Series system it sits before the NT-1 or MS-1c. In a broader context it is compatible with any streamer, Roon core, or network-connected DAC that would benefit from a cleaner incoming signal. It is one of the lower-cost improvements you can make to a streaming system that is already at a high level, and one of the ones that is consistently audible rather than theoretical.
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Specifications
- Type: Audio-grade network isolator
- Isolation: Active optical-electrical, dual-channel (independent transmit and receive paths)
- Ports: 2 x RJ45 — 1 input (standard), 1 output (optically isolated with electrical isolation washer)
- Network standards: IEEE 802.3 (10BASE-T), 802.3u (100BASE-TX), 802.3z (1000BASE-X), 802.3ab (1000BASE-T)
- Speed: 10 / 100 / 1000 Mbps auto-negotiating
- MAC address table: 2K entries
- Clocks: Dual femtosecond oscillators (one per transmission direction)
- Power supply: Dual-winding potted toroidal transformer, multiple LDOs
- LED indicators: Front panel — power status (1), link status (2); rear panel — speed, link and activity per port (2 per port); rear port LEDs switchable off
- Power consumption: Under 15W
- AC input: 100–120V or 220–240V, 50/60Hz (factory fixed)
- Enclosure: CNC unibody aluminium
- Dimensions: 120mm W x 205mm D x 44mm H
- Weight: 1.54kg
