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Step up from a Raspberry Pi with Allo Digital’s USBridge

  • Flavour of the month items come and go; we audiophiles have a proper thirst for the new. Some products leave an indelible mark though. Think NAD’s original 3020 amplifier or Linn’s LP12. Maybe the Devialet amplifiers or Roon software.

    Sonore’s microRendu is surely such a landmark product, not just halting the rise in streamer pricing but completely reversing it. £10,000+ streamers now have a tougher time justifying themselves against a sub-£1,000 upstart. Sonore hasn’t been shy with product development (V1.4, the UltraRendu etc.) but no doubt Jesus Rodriguez and co. have one eye planted on their rear view mirror; for audiophiles, the Small Board Computer is growing up fast.

    The reason is obvious; a simple Raspberry Pi streamer can be had for a paltry £50. Sure, it’s limited to USB audio output but it does the job and is one way to try out Linux in its many variants. If you can get on with it (and it’s getting easier all the time) you have a stepping stone to the world of add-on boards that elevate sound quality but at Guerilla warfare prices: Allo’s DigiOne provides a high quality SPDIF output.

    Another piece of the jigsaw is needed for those of us with USB DACs. Tapping Allo, that means their USBridge. Functionality is simple; ethernet in, USB out. Question: is it worth stretching to £140 when we get a perfectly serviceable USB output on the RPi 3 for well under half that amount?

    Some, including our publisher, beg to differ with my assessment of ‘serviceable’, arguing the electrical noise and jitter on the RPi’s USB output make it unsuitable for serious use. The RPi’s data bus is shared between USB and Ethernet, reducing bandwidth and generating noise of around 60mV. These figures come from Allo themselves who, good folks that they are, like to measure such things. Compare this to the USBridge where we see noise levels akin to a good battery. On paper the, USBridge’s benefits are clear.

    In reality, I have lived happily with an RPi, playing as Roon endpoint, for 12 months. Context is important, but my system – Ayre / Harbeth / Meridian Explorer 2 – is none too shabby, so I look forward to quietly disagreeing with Darko on that one.

    The RPi’s audible deficiencies only begin to show when compared directly to the USBridge which we buy as a package: Sparky SBC, USB shield, power supply, acrylic case and memory card. The Sparky is an RPi with knobs on; same concept, same size, same GPIO header (it can use RPi HATs), just slightly better engineered; the ethernet doesn’t sit on the same bus as USB and we get half the electrical noise of the RPi as a result. For the Sparky SBC, an optional external adapter is needed for WiFi. The onboard Ethernet is the recommended network connection. A Shield is simply Allo’s version of a HAT. Or should that be HUN? The USBridge slots onto the 40-pin connector on Sparky’s underside, not on top as per RPi HATs.

    As the USBridge is a complete package, we cannot add a USB Shield to a Sparky at a later date. Allo offer all or nothing for a plug and play experience. Everything comes ready assembled with your choice of operating system (DietPi or Volumio) pre-flashed to an EMMC memory card. Peel the protective brown paper off the case (a swine of a task but nevertheless providing good in-transit protection), follow the instructions to plug everything in, then power her up.

    I went for the DietPi option, which comes with a GUI that works well; it’s not a thing of beauty but greatly eases configuration. Had I read the manual at the outset, going from unboxing to playing music would have taken a mere 30 mins. Since setup, I’ve only used the GUI to power the USBridge down each night – a nice touch, saving the risk of corrupting data by yanking the cord. Oh – the GUI is also used pull down any software updates. This worked flawlessly for yours truly.

    Pre-installed software includes Roon, Squeezelite, Shairport (for Apple Airplay), GMRender (UPNP renderer), Netdata (control of the SBC), NAA for HQPlayer, Music Player Daemon, and WiFi Hotspot. I disabled everything but Roon and pushed onwards. System stability here is excellent (as is the RPi’s).

    Build quality is fine. The acrylic panels rattle slightly (being pre-built there’s nothing to tighten), and the look is distinctly DIY (unless you like innards on display a la Lloyds of London, in which case it’s state of the art). Mine lives in a cupboard so I care not about the hardware’s appearance but an extra £35 more gets Allo’s new aluminium wrap.

    No doubt a better power supply would also make a difference but to ensure a level playing field in comparing the USBridge to the RPi’s USB output, only standard power supplies were used. The Dietpi / Allo GUI combination was also used on both units.

    Pudding proof. Some components grow on you, releasing their charms over time. Not the USBridge — betterment of the RPi was readily apparent across the board from the get go. Neither was this performance delta a matter of perception or subjective value. Beth Hart’s Leave The Light On made me even more uncomfortable than usual, the USBridge’s greater clarity enhancing the dynamic range of her voice and increasing its potency. That increased clarity also made it easier to pull apart the strands of a complex mix like Live in Pompeii by David Gilmour; Great Gig in the Sky showed greater evidence of 3 singers wailing gloriously, one more than I’d thought via RPi.

    The USBridge stayed put in the cupboard for a month – out of sight out of mind – but familiar albums constantly reminded me of its presence through a consistently more compelling (read: more emotive) listening experience. Ain’t that what good/better audio is all about? It is for me.

    Cutting back to the RPi momentarily, individual voices or instruments melded into each other. With the USBridge they stood alone, more distinct, more discernable, more real. Audiodphile terminology neatly wraps this as ‘better separation’. Bass was similarly better defined. The flat out bonkers finale of Saint Saens’ Organ Symphony was just more majestic, more menacing, the acoustics more believable and the brass rasping with real bite. The slow 2nd movement also went a tad lower. Likewise the low pulsating synth underpinning the opening track of Beady Belle’s Cricklewood Broadway album bounced along with the USBridge; via the RPi it seemed to struggle to get going.

    Firing up the Raspberry Pi for a longer period highlighted its shortcomings on the USBridge. Everything was more homogeneous, acoustic spaces smaller and soundstaging flatter. Bottom line; it was less engaging. I stand by serviceable though, a £50 source in a £5k system sounds good but will easily be found out once something better steps up. For those on a budget or needing a second endpoint the RPi works well – mine will probably bring a Meridian F80 into the 21st century.

    For Allo’s USBridge, once you’ve tasted full fat there’s no going back though and £140 is within impulse purchase territory – you can’t say that about too many high/er network streamers. The thinking now moves to optimisation: how far I can take the USBridge? Third party power supplies might be the next playground. Then maybe I’ll stretch the D/A conversion out to a Mytek Brooklyn or similar to see if it can keep up. My gut feeling says it will. In terms of sound quality, the USBridge will better even a luxury laptop’s USB output and at £140 lays down its own challenge to the microRendu, kicking any such potential upgrade further into the (middle) distance. But then again, I’ve said that before…

    Further information: Allo Digital

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    Written by Phil

    Phil is a Brit living in deepest Devon. Think: Tolkien's Shire but with killer cream teas. He's been around since digital audio's inception - he even wrote his dissertation on the introduction of the CD - but today's developments in both music and audio gear make him think 'we have never had it so good'. Phil is a Music-First audiophile with wide ranging tastes (Trad Jazz excepted): 5000 albums in his local library with the remainder coming from Tidal.

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