Stack Audio

Link II Network Bridge

Price £1,075 inc Linear Power Supply

£725 without optional PSU

Digital file-based music collections have been around for a while now, but there are still plenty of refinements to be made. For example, sample rates have increased – certainly, since my early days of ripping MP3s to play on my Creative Labs Juke Box, that is! Then there are those focusing on how the digital files themselves are packaged, such as Bob Stuart at MQA. Others meanwhile, have charged themselves with the task of getting files from music libraries to listeners in the best possible way – one such person being Theo Stack.

Stack Audio was created in 2013, as a means by which he could focus on hi-fi sources of both the digital and analogue variety. As far as the latter goes, the company offers a range of upgrades for the venerable Linn Sondek LP12 turntable. As for the former – where zeroes and ones reign supreme – he offers the LINK network bridge, now in its second iteration. The secret sauce that joins these unlikely product ranges is Theo's desire to extract every last bit of detail from the music source and present it as accurately as possible.

I first came across the LINK at 2019’s Bristol Sound and Vision hi-fi show and was impressed by the performance of this seemingly unassuming device. One year later, and there is a version 2.0, so I was keen to audition it when I heard the news. The LINK II uses software developed by Ropieee, as opposed to the previous iteration's Volumio system. However, all the electronics and the lovely, understated casework is Theo's design. That said, John Westlake of Cambridge Audio fame – plus Peachtree, Pink Triangle and more – was called in to create the signal detox system that removes noise, reduces jitter and EMI and so delivers audio to the DAC and onwards as good as it can. It has a fine pedigree, then.

LINK II adds an improved clock circuit that’s said to have fifty percent less noise than the previous version, and it also works as a Roon endpoint – this is something I believe to be practically a deal-breaker these days. Under the hood, it uses a CM3 (Compute Module 3), much like the Mola-Mola Tambaqui DAC. Essentially, the CM3 is the heart of a Raspberry Pi. Theo told me that this is why the unit shows up as a Pi when using a network search tool. However, all the clocking, power circuitry, USB and Ethernet controllers are managed by Stack Audio's own circuit board.

UP CLOSE

All of this trick tech is wrapped in a case hewn from a solid aluminium billet, available in either black or – as per my review item – silver. The output is dedicated to a USB DAC of your choice, which of course ultimately has the biggest bearing on sound quality. Separating the LINK II even further from most other audio network bridges out there is a switch that lets you turn off the USB port's 5V output. This is an important distinction as this voltage throughput is a known source of noise. However, even though a mains-powered DAC might not need that handful of volts to make things work, some require power to sync with the source – so making this switchable is a good thing and covers both bases. You’ll also notice an HDMI port, but this has been disabled because video output is processor-hungry and harms sound quality.

Its connectivity options extend to an Ethernet port, a USB type B socket for attaching storage and one marked "Detox". The latter is for connecting a PC to the network bridge where the incoming signal is reclocked and mitigates any noise from the computer source getting any further through the chain. As well as the power port, there’s a connection for the Wi-Fi antenna. Also, there’s a USB port around the front of the LINK II which is covered by a piece of aluminium; this is held in place by a magnet, so is easily accessible.

The Link is a beautiful piece of equipment with an attractively robust yet lightweight feel. The finish is fab, and nothing looks likely to fall off in a matter of months. Price-wise, it sits in the same bracket as Lindemann's Limetree Network which has its own in-built DAC, although the German company also offers the less-expensive DAC-less Bridge.

Stack Audio offers an optional linear power supply for the LINK II, which was supplied for review as a package costing £1,075 in total. The benefits of high-quality power supplies are widely known, so given Stack Audio's focus on removing unwanted noise, its inclusion is unsurprising. I am told that this power unit features a UK-made precision wound toroidal transformer and audio-grade capacitors, along with noise suppression filters at both the output and input ends. Again, this is housed in an aluminium enclosure which sits on an elevated "advanced vibration dissipation" platform.

The device offers a range of playback and control modes that are accessible via a web browser. This isn't as scary as it might sound, as all that’s required is for the LINK II to be plugged into the same network as the tablet, laptop or PC you'll be using. Once you've tapped in its IP address, you are offered a few tabs and options. These include transcoding DSD to PCM, software or hardware volume control, wired or wireless networked operation, and whether you want to use Roon as your control device. You also get options to use Audirvana, Squeezlite, AirPlay, and more. As I access my NAS and subscribed streaming services via the clear and intuitive Roon system, this is how I set it up – although I started off by squirting tunes to it via the Bubble UPnP app on my phone, which worked seamlessly.

The LINK II was plumbed into my system via Chord’s Qutest DAC, but also spent time taking advantage of my Oppo UDP-205's DAC. Amplification was Anthem's STR integrated, out to Marten Duke 2 loudspeakers. Cabling was from Jorma Design, Tellurium Q, Vertere and Chord Company. Everything was sat on a SolidSteel S5 rack.

THE LISTENING

Energy, punch and instant engagement – that's what I was getting through the LINK II. Yes, this is a network bridge or – as some would call it – a streaming transport, so is just there to deliver those crucial zeroes and ones. Yet we now know there's more to it than that, as radio frequency interference and digital jitter play a detrimental part, for starters. As I discovered through the opening bars of R.E.M.'s What's The Frequency, Kenneth?, the LINK II grabs your attention and draws you in from the off. Bass was full-bodied and had real depth, yet remained fast and lithe.

That strong bottom end was wonderfully integrated with the rest of the frequency range, as Cliché by Fish showed me. Instrumentation was placed accurately and with equal attention. Additionally, there was none of that granularity that can sometimes plague lesser digital components. Instead, you’re blessed with a presentation with depth where vocal performances are given centre stage in a beautifully woven concert of articulate musicality. Indeed, in my opinion, the LINK II offered a much more expansive vista than Lindemann's Limetree.

Feed the LINK II with something a little livelier – such as Steve Vai's Dirty Black Hole at a time when the guitar maestro was joined by the explosive T.M. Stevens on bass, the phenomenally talented Devin Townsend on vocals and the percussive genius of Terry Bozzio – and it’s sit up and pay attention time. Yet even with this tinder-box of talent going full tilt, the LINK II never lost its composure. Instead it opened up the music and let the listener delve deeper. The raspy sax and trombone on Better Git It In Your Soul by Charles Mingus showed why digital audio no longer has to be flat and soulless. Everything about this track forced my feet to tap and my head to nod. Naturally, the bass playing also highlighted the unit’s excellent timing and rhythmic qualities, whereas the calls and handclaps brought the performance right into my room.

THE VERDICT

Again, Stack Audio has come up with the goods with the second-generation LINK. It makes music with quiet self-confidence instead of being bold and brash. From its organic aluminium form to straightforward browser-based set-up menu, care has obviously been taken at every step of the LINK II's creation to get the best from your digital library. The addition of the optional linear power supply adds a few hundred pounds to the price, but seals the deal – it’s a shame not to have it. So this small but talented bit of kit may not look fancy, but really delivers the sonic goods.

Visit Stack Audio for more information