Review: Giving the Pi a new HAT to wear for audio quality bumpView gallery - 13 images
New Atlas was recently contacted by the UK's JustBoom about "how the Raspberry Pi could potentially disrupt the high-quality audio industry." The company said that though some audio companies will demand many thousands of dollars for high-quality audio components like power amplifiers, digital media streamers and digital-to-analog converters, a "Raspberry Pi 3 in a case with a HAT on top can essentially do the same job for a substantially lower price point." Intrigued, we agreed to take a power amp and a DAC board for a test drive.
HAT stands for Hardware Attached on Top, and is simply an add-on board designed to fit on the Pi's GPIO (General Purpose Input/Output) connector and give the popular mini computer additional functionality. It usually has one mounting hole at each corner, which line up with those on the Pi. The JustBoom Amp HAT kit comes with eight plastic screws and four short support tubes to secure it in place. Though available to buy on its own, we were sent a kit that includes a Raspberry Pi 3 Model B, a snap on/off plastic case and a power brick.
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The 6.5 x 5.9 cm (2.5 x 2.3 in) Amp HAT is also compatible with A+, B+ and 2B flavors of Pi, as well as the Zero (though the company does produce a special version of the device for the Pi Zero). There's also a microSD card sporting a Max2Play operating system image, but the JustBoom board is compatible with OSMC, Volumio, Roon, PiCorePlayer, PiMusicBox, OpenELEC software and more, too. The kit also comes with an IR receiver, but adding this to the Pi board will involve breaking out the soldering iron and setting up LIRC before grabbing the JustBoom IR remote.
The JustBoom board essentially gives the quality of the audio output of the naked Pi a bit of a nudge in the right direction, while adding passive speaker connectors so users don't have to output via the Pi's 3.5 mm headphone jack. It can turn the Pi into a local hi-def audio player when hi-res music files are loaded onto a microSD card or USB thumb drive or, with the help of the Pi's cooked-in Wi-Fi, users can listen to tunes streamed from the cloud or network storage, or tap into the numerous internet radio stations available.
It's rated at 30 W RMS stereo into 4/8 ohms, which was more than enough to drive our bookshelf speakers – not that I have any neighbors, but if I did, I'd definitely need to reduce the volume by at least half so as not to offend. And the board's TAS5756M Class-D amplifier has built-in digital-to-analog conversion for up to 32-bit/192 kHz audio resolution.
The Amp HAT is slotted onto the Pi's 40-pin GPIO connector – no soldering iron required – and the one power brick serves the whole system, so no need to plug a separate USB power cable into the Pi. Tinkerers will also appreciate that JustBoom makes all of the unused GPIO pins available for projects on the Amp HAT, allowing for the addition of sensors, buttons, LEDs and so on as a project dictates.
And we're off... kind of
The setup is described as plug and play, which suggests that the Amp HAT kit just needs to be cabled up and powered on and it's ready to rock. In fact, it's a little more involved. Our kit came with a Max2Play image already loaded onto the microSD card installed in the Pi's slot. After connecting speaker wires to positive/negative outputs terminals to the front of the Amp HAT, we then had to set up and configure the Max2Play software to change the default audio output of the Pi to the Amp HAT.
The guide at the JustBoom website is fairly straightforward, with a rather glaring omission. In order to configure the software, the Pi/Amp HAT needs to be powered on and connected to a home/office/media room network. Actual configuration takes place through a browser running on a laptop or computer connected to the same network. This is not specified in the instructions. Once the laptop and the Pi/Amp HAT start communicating, configuration should take about 5-10 minutes.
This includes setting up the Kodi media player, originally called the XBox Media Center when it launched in 2003, using a monitor, mouse and keyboard cabled up to the Pi. And that's where we had a few headscratching problems. Though Kodi booted up fine, the JustBoom audio output option wasn't displayed in the settings so the audio output came through the Pi's headphone jack, and not the Amp HAT.
After running through a few settings and configs with JustBoom tech support, we had to download and install a fresh Max2Play image onto the microSD card. This did the trick, and setup and configuration proved successful. Diagnosis – faulty/corrupt software image on the supplied microSD card. Due to such shenanigans, the plug and play setup and use scenario took a good deal longer than 5-10 minutes, but hats off to JustBoom's tech support for the assistance needed to get us up and running.
Then came another rather arresting discovery. The volume in the Max2Play config screen was set to 100 percent by default, necessitating a hasty pause in the music and some quick mouse action in the config software running on the laptop. There are no hardware volume controls for post config output level adjustment, but the keyboard attached to the Pi can be used to raise and lower the volume.
JustBoom also offers an optional IR remote, but to use this, some software needs to be installed and configured and the IR receiver included in the kit has to be soldered to the HAT. The IR remote allows for playback control, menu navigation and volume adjustment from up to 10 m (33 ft) away.
Tweaking settings and adding extra functionality via Max2Play proved fairly straightforward, but scheduling music to play or watching videos and so on was done via the Kodi media center. We also tried out other Kodi-driven audio software – OpenELEC and Raspbian – and an open source audiophile music platform called Volumio. The latter proved the easiest to set up and use, and offered the quickest way in, and we felt it offered a much closer to plug and play experience than the supplied Max2Play, allowing us to tune into internet radio stations or feed in digital music via the USB port or network-attached storage with intuitive ease.
Pulling hi-res audio out of the HAT
Despite its small size, the Pi/Amp HAT combination proved loud enough for party use, though the vast majority of the time we used it to stream hi-res music from Qobuz, access internet radio stations, or raid our network attached music library. While no match for our living room hi-fi setup, the quality of the output was pretty good – not just a marked improvement on the Pi's built-in audio capabilities, but also giving our mid-range Wi-Fi music service streamer a run for its money.
Adjusting the bass response, enhancing mids or shaving a little off the top end to suit personal preference or room/space conditions is not as easy as simply turning knobs forward or back. The software media player used for much of the review, Kodi, is fairly basic on first boot, and doesn't include the ability to adjust EQ. But like apps for smartphones, add-ons can be installed to get access to extra features, like audio EQ or YouTube videos.
Max2Play glitch aside, we found this Pi-powered music box easy enough to use, though we do feel that folks new to the Pi universe might find it simply too fiddly and involved and instead head for an easy setup one trick pony network streamer that complements the living room hi-fi stack or TV with minimal fuss and effort, even if the initial cash outlay turns out to be quite a bit more.
That said, JustBoom does make the financial case for Pi-based audio quite compelling. Existing Pi owners can buy an Amp HAT for £60 (about US$75) – or £24 for the Pi Zero flavor. An Amp HAT case, if needed, costs £13. A power supply and microSD card will also be needed, but you're still likely looking at somewhere around £100 for the whole setup.
For those who would rather not take the piecemeal component approach, the Amp HAT kit we were sent costs £145.
Different HAT, same high quality audio
JustBoom also sent us a DAC HAT to try. Like the Amp HAT, it's plonked onto the Raspberry Pi's 40-pin header and is designed to give Pi audio projects a sound quality bump. At its heart is a Burr-Brown PCM5122 chip capable of supporting files up to 32-bit/384 kHz resolution (though Linux driver restrictions max the frequency out at 192 kHz) and a Texas Instruments TPA6133A2 headphone amplifier.
The 6.5 x 6.6 cm (2.5 x 2.6 in) board gets the power it needs from the Pi, and outputs to a 3.5 mm headphone jack and RCA ports. Configuration and setup is the same as with the Amp HAT, which means that it's not as simple as merely positioning a desktop or pocket headphone amp/DAC inbetween a digital music source and some ear candy, but the audio routed through the media software running via the Pi sounded pretty darn good to our ears.
The DAC HAT carries a recommended retail of just £30 (approx. $37) on its own, or £115 as a kit (which includes a Raspberry Pi, case and power supply). Even though the Pi-related project possibilities are tempting, we'll still be sticking with our capable, easy to use and relatively cheap DacMagic XS from Cambridge Audio for everyday use.
The bottom line
We've now spent a few weeks with JustBoom's Pi HATs and, while we don't think the JustBoom HATs are going to disrupt the high end audio industry any time soon, we can see the Amp HAT and DAC HAT helping to breathe new hi-res life into a maker favorite, giving the Pi the power to really satisfy in the audio department and doing so without breaking the bank.
It wasn't quite the plug and play music experience we imagined, but could be a good way for audioholics to introduce themselves to the awesome world of Pi, or serve as an inexpensive way to fill the house with high resolution digital music. Or maybe a mix of both.