A better sounding Raspberry Pi with JustBoom’s Digi HAT

Previously on Raspberry Pi: a €35 palm-sized computer deployed as Roon/MPD-streaming endpoint. Drama! Intrigue! There must be a plot twist, right?

Yessir: sound quality. As a network streamer, the Raspberry Pi alone can’t keep pace with the bigger boys like the AURALiC Aries Mini and (especially) the Sonore microRendu.

On Giant Sand’s “Monk’s Mountain”, run through the Vinnie Rossi LIO super-integrated and Dynaudio Special Forty loudspeakers, we hear hints of micro-dynamic rigidity where previously, with the Aries Mini, a sense of musical ease was more pronounced. The Raspberry Pi bleaches once vibrant tonal colours. Its broader gestalt makes music sound more mechanical than its audio-optimised rivals. Not what we want from Howe Gelb’s porch-front pluckings.

Alas, applying iFi Audio’s low-noise SMPS (€50) makes only the smallest of discernible difference. This tells us that the official Raspberry Pi power supply isn’t wholly to blame for its USB output’s aural disappointment.

Experience tells us that the jitter correction promised by DAC manufacturers doesn’t render their converters immune to upstream changes where jitter and electrical noise can still cause music to sound somewhat anaemic and rigid, even with data-buffering and reclocking applied by the DAC.

The Raspberry Pi was designed to be an affordable, multi-purpose device for everyone, not a digital audio strongman aimed at the discerning listener.

Jack of all trades, master of none? Time for some third party intervention.

Seeking to extend the Raspberry Pi’s audio functionality and improve upon its base-level sound quality are JustBoom, British manufacturer of audio HATs.

From their website: “Audio. It’s what we do. We make our products simple, easy to use, and always keep in mind that high definition music should be affordable and enjoyed by friends, family… everyone.”

A HAT (Hardware Attached on Top) is a circuit board that fits directly onto the Raspberry Pi’s 40-pin GPIO connector – no soldering required. Upon system boot-up, the Raspberry Pi auto-detects its newly-attached HAT and automatically loads/configures any associated drivers – no user intervention required.

JustBoom offer three HAT models: an Amp HAT (£60) with onboard D/A conversion to drive passive loudspeakers; a DAC HAT (£30) to feed a pair of powered loudspeakers or amplifier; and a Digi HAT (£30) that extracts digital audio from the Raspberry Pi below for output via its own TOSLINK and galvanically-isolated, 24bit/192kHz-capable coaxial sockets. Jitter reduction comes courtesy of a WM8804GEDS S/PDIF chip.

Quoth JustBoom’s product page: “The JustBoom Digi HAT is a high resolution digital audio output add-on board for the Raspberry Pi. Simply stack the plug-and-play add on board (HAT) onto your Raspberry Pi A+, B+, 2B or the new 3B and it will be ready to use immediately. The JustBoom Digi HAT produces an unmodified, high quality, digital audio data stream for bit-perfect transmission to your hifi system.”

“The HAT uses the I2S interface for its audio input which reduces CPU load on the Raspberry Pi compared to USB solutions. It is also powered directly from the GPIO header so no extra cables or power supplies are required to connect to the Raspberry Pi.”

JustBoom also offer complete kits that include a Raspberry Pi 3, HAT, custom plastic case, ‘official’ 5V power supply, micro SDcard and connecting cables (where required). This Brit company’s trump card is its extensive range of online support articles; mandatory reading for newcomers to the Raspberry Pi-based audio world.

In putting together JustBoom’s Digi HAT kit (£115) on my kitchen table, considerably more time was required to add the rubber feet to the custom case (available separately for £13) than was needed to carefully slide the Digit HAT board onto the Raspberry Pi’s 40-pin connector and secure it with plastic screws and risers (also supplied). JustBoom’s meticulously detailed step-by-step tutorial made assembly so simple even my Mum could do it.

They’re super-fiddly to insert into the custom case’s base but don’t be tempted to skip out on the little rubber feet. Lightweight in hand and on table-top, this Raspi two-fer slide needs all the help it can get to stop it from falling off the back of the hifi rack and into the cable salad below.

Moreover, a fully-assembled Digi HAT-ted unit is light enough to affix directly to the rear of an active loudspeaker with two strips of double-sided sticky tape.

Don’t find the Raspberry Pi 3 + Digi HAT package compact enough? Seek out the Raspberry Pi Zero and pair it with JustBoom’s Digi Zero pHAT (£24) and custom case (£13).

The Digi HAT’s functional advantage over a solo Raspberry Pi is extended connectivity. Not all digitally activated loudspeakers specify a USB input. Many, like the Dynaudio Xeo 2 and Audioengine HD6, are TOSLINK only. That makes them Ideal candidates for a JustBoom HAT-ted Raspi.

The Digi HAT also strikes the bullseye for those wanting to add an affordable Roon Endpoint to a single Devialet Phantom – or a pair of Phantoms via the signal-routing Dialog box – where the only input is TOSLINK.

Furthermore, we often find see many legacy DACs restricted to S/PDIF inputs: TOSLINK and/or coaxial. And some modern-day amplifiers, like Arcam’s SR250, arrive sans USB. The Digi HAT’s TOSLINK output bridges these connectivity gaps. It’s a joiner of worlds!

Before we can get up and running with music however, the Digi HAT must be selected as the preferred output device within the host device’s operating system.

In Volumio, or JustBoom’s re-branded Volumio, the Playback Options page is where we tell the Raspberry Pi to send all digital audio upstairs to the Digi HAT. Once again, JustBoom’s web-based tutorials walk us through the process step-by-step should we need a little hand-holding.

Official Roon support remains TBA. At time of writing, JustBoom recommend DietPi as a Roon-capable OS. Otherwise, Roon Bridge can be installed to Volumio/JustBoom via the command line; precisely why I took the time to detail the procedure in an earlier article.

Things get spicier when we shift our focus from the TOSLINK output to the coaxial.

Hooked directly into the Vinnie Rossi LIO and its DAC module’s BNC socket via BlueJeans digital coaxial cable, the greyed-out tonal colour and micro-dynamic reluctance heard from via the Raspberry Pi’s USB output is dialled back. Dialled back to such an extent that I have a hard time separating the sound quality delivered by the Digi HAT’s coaxial from that of the AURALiC Aries Mini (€499).

For those happy to do without the Aries Mini’s Lightning DS server functionality, its SSD-hosting undercarriage, D/A conversion and USB output, this is a significant discovery, doubly so given the price differential between the two network streamers.

The JustBoom Digi HAT is quite the find for those already in possession of a D/A converter and looking to add a high/er quality network streamer whilst adhering to a super-tight budget.

Further information: JustBoom