Let's start with a basic fact: Raspberry Pi's were not intended to be high-end audio devices. Just tiny, work-horse computer boards that could be applied in a variety of ways. Try listening to the Pi's own headphone output - audiophile? Far from it.
A mini-industry has sprung up to make use of the data-streaming abilities of these boards and add-on's have been created to allow the music-lover to build cheap and effective digital audio sources. BUT the Pi is a noisy little critter, electronically, not refined with expensive circuitry to damp-down unwanted interference that might affect sound quality. And a major hinderance so far has been that the add-on audio boards have been dependent on the Pi for power and processing, carrying unwanted garbage into the audio signal chain.
The Allo DigiOne Signature turns this around. IT provides the power and uses the Pi as an add-on to receive and initially process the data-stream that it then turns into an SPDIF audio signal.
To achieve this, the Signature has 2 boards: The 'Dirty' board is directly attached to the Pi via the normal 40-pin connector. This board provides power to the Pi and receives the I2S data that the Pi pulls in from the network. the Wolfson chip on this board converts that into a raw SPDIF format that gets passed onto the next stage.
The 'Clean' board. This is where the magic happens. Connection to the rest of the unit is through a smaller 8-pin plug that is galvanically isolated from the other boards. The clean board has a separate power connection and is dedicated to one task - making sure that the SPDIF data is as exactly synchronised as possible. So that when the receiving DAC gets that data-stream, it can turn it into the most accurate analogue audio waves.
So the clean side has special ultra-low jitter clocking chips, high-quality components which can be fitted due to the extra space that the 2-level approach provides, and a substantial capacitor to ensure the smoothest possible electrical flow. Output is via BNC or RCA sockets - no optical as these are just too prone to jitter.
Assembly is the usual fun and cursing (I always make mistakes putting these things together) but you end up with something that looks pretty cool - the extra height from the 3-deck unit has more solidity to it.
Then its time to hook it up; simply swap over the Volumio SD card from the standard DigiOne into the Signature (they use the same setting), Then the ethernet and coax cables, and then firstly power to the Clean board from my LPSU (needs to be powered on first so the Pi can find it) - then power to the dirty board and the Pi from a standard 5V/3A wall-wart phone charger. On power-up the SQ was initially a bit 'dry' so I let the unit warm through overnight.
Sound: well, I fall very easily into gushes of abundant enthusiasm so I will try to exercise a little restraint here.
It's Bloody Amazing !!!!!!!!
Clarity. Control. Authority. There is a new sense of immense space in the music where room is given to every shade of detail. Bass is deeper and intenser.
Suddenly I experienced a familiar recognition. For a while I had a pair of Magnepan MMG panel magnetostatics in the system and these provided a glorious image that allowed you to look into the music as you would a painting. That sense was back - but now with my modest, refurbished Cube 3's doing the work and providing a rich, living vibrancy that the MMG's never quite could.
Actually I'm gobsmacked. This is now an audio experience of depth and impact that I have never had before. That's the fun with this hobby - these moments of total revelation when you think 'Shit - I didn't realise it could sound like THAT.'. Says something about the transparency of NVA gear in that every time the source improves, the rest of the system just glows and shines even better.
It might seem that the Signature is an expensive way to go for a Pi-based streamer, but it will reveal treasures beyond price. Honest.
