Hardware Reviews

Stack Audio Link II


It’s only been a year since I reviewed the original Stack Audio Link but the streaming world runs a little faster than most so it’s not surprising that Theo Stack has managed to make some important changes to his small but beautifully formed streaming bridge. It’s probably worth reiterating why this is called a bridge rather than a streamer, it’s not complicated and merely refers to the absence of a DAC. There is no formal definition of a streamer to my knowledge but if there were then a network bridge with DAC would be a sensible one to go for.

The Link II still inhabits a case that’s machined from solid aluminium billet and retains the same connectivity with output dedicated to USB. Unlike 99.9% of network bridges this one has the option to switch off the 5V output to the USB connection, this is a known source of noise that isn’t necessary with powered DACs so turning it off has to be a good thing, the only drawback is that many DACs fail to sync with a USB source that doesn’t have the voltage. The other connections include a vestigial HDMI output, this has been disabled because video output is processor hungry and therefore detrimental to sound quality. Not to mention unlikely to be used by most audio enthusiasts.



The main changes that brought about the Link II are the introduction of a new clock that’s said to have 50% lower phase noise than the first Link, and new software. The latter has changed from Volumio to a stripped down end point software designed to work with UPnP. You can also run Link II with Roon which is Theo Stack’s preference for understandable reasons, it’s very intuitive, informative and extremely stable. As streamers live or die on the consistency and reliability of their control software, having access to something like Roon is a real advantage. It’s pricey approach however with an annual cost that’s just shy of $120 or a lifetime licence for $700. Which is why you might prefer to use one of the many free UPnP control apps on the market.

In its standard guise the Link II comes with a wall-wart power supply of the switching variety, but there is also an upgrade power supply available. This weighty linear supply (below) uses high quality parts including noise suppressors on in- and outputs, has an anti-vibration platform under the transformer and comes in rather nice anodised aluminium case to match the Link II. A detachable (see potentially upgradeable) lead to take 18 volts to the Link II.


There are a number of connections on the Link II, most are self explanatory but the one marked Detox less so. This USB B input is for PCs and reclocks the incoming signal, removing much of the noise from computer sources in the process. There’s also a second USB A connection alongside the one for the DAC, this will be for use with USB drives when Stack add this feature to the firmware.

While you can control what the Link II sends out with Roon or a UPnP app changing the way it operates needs to be done with Roon or via a web browser. There are quite a few variables including whether to transcode DSD to PCM, software volume control, updating the software, wired or wireless operation and whether you want UPnP or Roon control. There are also options to use Airplay, Spotify and Squeezlite among others. Many are for PC users and if like me you have a dedicated music server the only key choice is the control method.


Sound quality
I started out using the Link II with an Auralic Vega G2.1 DAC as it’s a fabulous converter but, it seems, not one that plays nice with this streamer, the main issue being that changes in sample rate resulted in noise rather than music. Not consistently but often enough to encourage a change to my regular DAC, an iFi iDSD Pro, and this partnership worked extremely well. The Link II is not as full bodied as the Auralic Aries G1 that I generally use but it is a third of the price so that’s hardly surprising, what is impressive is its all-round sound quality. The leaner balance does not preclude it from delivering high levels of detail and excellent timing, in this respect it is clearly superior to the original Link and to most other streaming bridges anywhere near its price point.

The pace on Van Morrison’s Jackie Wilson Said is clear and the track energised by the brass section, you really have to sing along to it even when sober. Bass is a notable strength as well, it really does go deep, there’s no sense of thickness to the bass so it’s as nimble as the rest of the audio band and this is a key to the Link II’s timing. I really enjoyed the tension that this degree of resolution brings out in certain recordings, In a War Such Things Happen by Conjure is inevitably not a lullaby and the Stack lets you know about it without adding any edginess or grain to the sound as is often the case with more affordable digital components. It doesn’t lose composure when the music gets lively either which is very appealing if you like high energy music, and it keeps you listening long into the night, especially when playing great albums like Michael Chapman’s Rainmaker.


Adding the linear power supply brings a more refined, smoother sound that can take the exposure provided by a high end system, which is effectively magnifies the pros and cons of any source component. Now Bill Evans’ Waltz for Debby sounds younger than it is albeit still in dual mono with instruments kept to each channel and only the audience getting the stereo treatment. But there is more life in the piece and greater articulation from all the instruments, this goes up a notch with Patricia Barber’s Bye Bye Blackbird where the vocals are nothing short of phenomenal and the band distinctly present in the room. The big power supply also enhances the sense of three dimensionality in the sound, adding depth to the beautiful phrasing and increasing the qualities of focus and timing which make for a more immersive experience with any material.

I tried turning of power on the USB connection and discovered that a piece of music that had previously sounded pretty good was now making so much emotional impact that I had to pull myself together. It was difficult to put a finger on what had changed but clearly a veil had been lifted and the musical message was coming through in powerful fashion. Sadly it became clear that the iFi DAC wasn’t entirely happy with this state of affairs because a few tracks later it decided not to play ball until I switched the voltage back on. I guess that USB receivers need the confirmation once in a while.


I wasn’t able to try the Link II’s reclocking PC input because my Macbook has died but this is a whole other aspect to its capabilities that other bridges do not offer. In many respects it provides a pathway from computer based file streaming to the network based approach, extracting excellent results from both approaches in the process.

I am very impressed by the Stack Link II, it offers a standard of sound quality that you expect of a streaming bridge at twice the price alongside the build quality of something more expensive. How many streamers have machined from solid cases at any price? I used Roon for most of my listening and have to say that it adds a degree of sophistication that while it carries an extra cost, makes the experience very rewarding indeed. The first Link was good but this one has raised the bar quite dramatically and anyone wanting to hear why streaming is proving so popular would be crazy not to give it a try.


Link II
Type: Streaming bridge
Streaming protocols: Roon, Audirvana, Squeezelite, UPnP/DLNA, Airplay (Shairport-Sync), Spotify (Librespot), HQPlayer (coming soon)
Inputs: Ethernet, USB, Wi-Fi, Bluetooth
Supported File Formats: FLAC, Apple Lossless (ALAC), WAV, AIFF, MP3, AAC (in M4A container) MQA (only if DAC supports unfolding), DSF (DSD), DIFF (DSD), DoP (DSD)
Supported Digital Formats: PCM from 44.1kHz to 384kHz in 32Bit, DSD64, DSD128, DSD256
Control Software:, OpenHome compatible control software (BubbleUPnP, Mconnect Kazoo etc), Roon
Dimensions WxHxD: 174 x 25 x 140mm
Weight: 1kg (without external power supply)
Finishes: anodised black or silver
Warranty: 3years

Link Linear PSU
Output: 18V, 1.5A
Size HxWxD: 60x120x200mm
Weight: 2kg
Finishes: anodised black or silver
Warranty: 3years

Price when tested:
Link II £725
Link Linear PSU £400
Link II & Link Linear PSU £1,075
Manufacturer Details:

Stack Audio
T +44(0)1626 24 9005


Streaming bridge/reclocker


Jason Kennedy

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