Digital audio moves forward rapidly, manufacturers can’t rest on their laurels. Today’s wunderkind quickly becomes tomorrow’s me-too, fantastic for consumers even if it does encourage the premature onset of an upgrade itch.
My own journey is a case in point. Both my DAC and network streamer have changed three times in two years with one constant: all three streamers were based on Single Board Computers (SBC) like the Raspberry Pi (RPi). It’s not the only approach but the flexibility and off-the-shelf nature of SBCs that are attractive to manufacturers. The community developed Linux-based operating system(s) means much of the heavy lifting on the software side has already been done.
Allo’s original USBridge (review here) comprised a HAT (Hardware Attached on Top – an add-on board) mated to a single board computer. Not an RPi computer but Allo’s own version of an SBC called a Sparky. Its 40pin slot conformed to the RPi standard to accommodate RPi HATs.
The USBridge Signature is different. It uses the CM3+ ‘industrial version’ of the RPi – the green board in the photos – for its data processing. According to Allo, this is the CPU from the RPi3B. That leaves Allo to develop a motherboard (the black board in the photo) to handle networking, clean power distribution and the all-important USB output/s. Note how the CM3+ sits within Allo’s board.
This increased flexibility allows for better optimisation of sound quality – the USBridge Signature’s motherboard uses thirty LDO (low dropout) voltage regulators to fine-tune the power fed to its various stages. This might sound familiar to some; the £600 Pro-ject Stream Box S2 Ultra is CM3-based. It also had meticulous attention paid to distributing clean (read: lower noise) power within its circuitry. To the extent that Pro-ject says it doesn’t really benefit from an upgraded external power supply. How does the $249 / €271 / £240 USBridge Signature fare in comparison?
Purchased as a pre-assembled device, the USBridge Signature Player is conceptually simple: Ethernet in, USB out. Some call this a network bridge. Others call it a network streamer. Same same. A USB-C 5 volt / 3 amp power supply is required but not supplied – see below – and the HDMI connects to an external display if required.
A ‘clean’ USB 2.0 output sends digital audio into the DAC. Two additional USB sockets allow for BT or Wi-Fi adapters. The USBridge Signature’s networking is Ethernet only. The SD card is for the operating system (OS). There’s also a ground terminal that we shouldn’t overlook – explanation below.
Allo will pre-load the OS at time of order. Choose between DietPi, Volumio, Moode or Max2Play. I went with DietPi for its Roon integration. Any other RPi OS should work – DSD512 files call for an additional driver to be installed (which is already built into DietPi, Moode and Max2Play). Note that the OS determines gapless play or otherwise. Also which data rates are available; the CM3+ itself is capable of PCM384 and DSD512 and will pass MQA to suitably DACs.
Want more digital outputs? We can add the DigiOne Signature HAT to the motherboard’s 40pin socket to give us S/PDIF via RCA and BNC. It uses the same case as the USBridge Signature, just a different back panel. This HAT and slightly revised case adds $220 / €245 / £220 to the price and requires an additional power supply brick.
For the USBridge Signature, any 5 volt / 3 amp supply should work. £8 gets us the stock RPi wall wart (Allo can supply if needed). Circa £50 buys an iFi iPower or Allo’s new Nirvana, both switch-mode power supplies rather than linear-regulated. Both aim to reduce electrical noise. Allo’s £170 Shanti power supply has two galvanically-isolated 5V outputs (3 amps & 1 amp – the latter will power the DigiOne Signature if installed)). Alternatively, £300 welcomes SBooster’s BOTW Eco charger – expensive but with the USBridge Signature in tow it’s still less than a Pro-Ject Stream Box S2 Ultra.
With so many alternatives, I focused on Allo’s Shanti supply and a standard RPi wall wart.
Looks & build
Arriving in a plain black aluminium box with a circular cutout on top for thermal management, the USBridge Signature won’t win any beauty pageants. That said, its looks are streets ahead of the Allo ‘steam punk meets Lloyds of London’ vibe as typified by Allo’s Boss Player and the original USBridge.
Build quality is similarly equivocal; the aluminium case is lightweight and flimsy but avoids the DIY feel of Allo’s acrylic cases. Pop the top and everything looks solid enough, it’s just no heavyweight. That means we should be careful with stiff or heavy cables that might drag the unit around.
Gold Note’s £1264 PA-10 power amplifier (review soon) drove Graham’s £2,300 LS6 standmount loudspeakers, connected by Tellurium Q Black 2 loudspeaker cables (£270). Gold Note’s matching £2,500 DS-10 (review here) acted as digital pre-amplifier and USB DAC. The latter’s internal streamer provided a counterpoint to the USBridge Signature, in addition to the Pro-ject Stream Box S2 Ultra.
Listening – comparing to the Gold Note DS-10
First impressions with the Shanti power supply in play are good. The Allo streamer gives a beautifully balanced sound, with neither heavy bass nor prominent treble. And there’s plenty of detail without player definition coming across as overly etched. In character and performance, the Allo sounds broadly similar to the Gold Note DS-10’s streamer. However, there exist a few minor performance deltas: the DS-10 sounds a little more open, its bass is marginally tighter and I hear slightly better delineation between instruments. Performers are more palpable too, the sense of ‘being-there’ greater.
In my email communications with Allo, the company suggested I pay attention to the USBridge Signature’s grounding setup. Normally components are earthed individually, Allo recommended a star-earth arrangement whereby they share a common ground. So the USBridge’s earth terminal was hard-wired to the Shanti. Allo has measured the reduced noise floor this produces. I also wired the Shanti to the DS-10’s chassis. Allo thought that might reduce noise further – and it appeared to. With each extra earthing step came a small but noticeable gain in clarity. For example, the opening guitar on Marta Gomez’ ‘Lucia’ (from Entre Cada Palabra) cuts through the silence more cleanly, the subtleties of fingering easier to hear. The cumulative improvements proved worthwhile.
The DS-10’s streamer better still communicates a performance space’s sound (should it exist). The Italian plays more to light and air whereas the USBridge Signature is slightly darker and a bit meatier. Choosing between them will be a question of system matching. With a combined price of £400, the USBridge Signature and Shanti power supply sound fantastic in my book.
£400 too much for entry-level systems? No problem – out with the Shanti, and in with a standard £8 RPi power supply. Total cost £250.
Into the review system, this pairing goes and, at first, I find myself slightly flummoxed, expecting a MUCH larger drop off in sound quality. The similarities to the Shanti-fronted combo shout much louder than the differences. With the low-cost power in play supply, there’s a little less clarity, bass isn’t quite as tight. Not a huge delta. Neither does the comparison to the DS-10 streamer embarrass the £250 duo. That’s impressive given the cost of the rest of the system. The USBridge Signature would appear to be another long-legged component – able to live comfortably in a system that’s upgraded over time. And we can always add a better power supply to help it play keepy-uppy.
Listening – comparing to the Pro-ject Stream Box S2 Ultra
All change – back in with the Shanti power supply and the more carefully arranged earthing to see how an optimised USBridge Signature compares to the Pro-ject streamer.
And wow. Sounding a little cleaner, the USBridge Signature just shades the Stream Box S2 Ultra. We note more air around performers, a slightly firmer low and end and, perhaps one hallmark of great audio, better sorted complex mixes. Lest we get carried away, we’re talking about very marginal deltas. Only forensic listening revealed these differences. Disconnect the second earth lead – between Shanti and DS-10 pre-amplifier – and the Allo falls back to the Pro-Ject’s performance level.
On looks and build, the USBridge Signature doesn’t wear its RPi origins on its sleeve but neither will it put a pride-of-ownership swagger in our step. That’s the worst thing I can say about the Allo streamer. In every other respect, it’s a fine device.
Juiced by the Shanti and with earthing sorted, the £400 duo just nudges out the £600 Pro-Ject Stream Box S2 Ultra. Quite an achievement. And yet the USBridge Signature also performs very well with a low-cost 5V supply, making it a slam-dunk for those on tighter budgets. Flexible, reasonably priced and sounds excellent. What’s not to like?
A matching DAC that sits atop the USBridge Signature is in development – think grown-up Allo Boss Player. Very interesting.
Further information: ALLO