AirBoxOne by Jordan Stockton

Read how HifiBerry user Jordan Stockton set up his AirBoxOne using a HiFiBerry DAC+ pro.

Goal: Put a no-comprimize AirPlay server and a low distortion amplifier in a single box that I would never have to touch.  Set it and forget it!
Rationale: IMHO, there is nothing quite as simple as using AirPlay to play music from an Apple device.  And unlike other types of streaming protocols, AirPlay signals can be completely uncompressed.  So it seemed that the ultimate minimalist audio system was an AirPlay server (streaming uncompressed audio from a service like Tidal) coupled to a modern and thoughtfully designed switching amplifier.  I couldn’t find a commercial alternative that checked all the boxes: single purpose streamer-amp, powerful clean and neutral amplifier, no additional software required on my phone, automated power controls (so you don’t ever have to touch the box). And I needed a project!
Computer: Raspberry PI 3, running Jessie
DAC: HiFiBerry DAC+ Pro
Amplifier: Class-D Audio SDS-250 Power Amplifier (rated at 2 x 125W @ 8 Ohms)
Power supplies: Toroidal AnTek 400VA Transformer w/Class-D Audio capacitor bay (for the PowerAmp), DMioTech DC 5V 5A switching supply (for the RPi)
Chassis: Aluminum Enclosure from Douk Audio (216mm x 154mm x 316mm WxHxD)
Relay: Uxcell BEM-14840DA 24-480V AC to 3-32VDC (not pictured) 
Button: 16mm RGB-LED momentary switch (from Adafruit)
Random: speaker terminals, potentiometer knobs, and jacks (from eBay and Adafruit)
Custom Python for power control logic
I tried to squeeze the whole thing into a cabinet that occupied the smallest possible footprint on the shelf.  And this meant machining a “second story” out of 3/16” aluminum so that I could stack the Pi and the DAC and the amplifier on top of the power supplies. For streaming, I found  the excellent ShairPort-Sync software, maintained by Mike Brady, to be incredibly well documented and quite stable.  The Pi switches on the amplifier (using a solid state relay) when ShairPort-Sync is streaming, and turns it off after 120 seconds of idle time.  The momentary switch/LED on the front acts both as a soft power-on using the Pi onboard “run” headers, a soft restart trigger through the GPIO, and an LED status indicator for the amp/relay.  In practice, I set the right and left channels to a reasonable mid-level volume and then make all of the day-to-day volume adjustments with my phone. I liked the clean look without any logos or text (and I am lazy), so I left the front panel blank.  It sounds great!  The combination of the HiFiBerry DAC+ Pro and the amplifier from Class-D audio makes for an incredibly clean, detailed, and powerful one-box audio solution.
Next Steps:
I’m keeping the AirBoxOne in my attic, which can get stupidly hot.  The enclosure is currently 100% sealed, which worries me given the hot environment, so I am planning to install a cooling fan on the back panel and a smart temperature sensor that can help regulate the interior temperature when needed.  The goal is for the unit to run without the fan until it is absolutely required, which I hope is almost never.  But currently, the CPU temperature ranges in the 75-80 deg C range, so I like the idea of having active cooling as a backup.

May 23, 2017

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