[mbritt]

This write up is a comparison of Roon endpoints into Schiit ModiMulti (no Unison) and Bifrost 2 (Unison USB). Specifically the difference in Pi4 USB vs Pi3 with a HAT (Hardware Attached on Top).

I've been using a RaspberryPi 3B+ with an Allo Digi One SPIDF Hat as a Roon endpoint for the last couple of years (the black plexi box in the back of the photo). It sounds great separating the audio signal from the noisy USB on the Pi and sending it out cleaned via the coax S/PDIF. This setup took the place of a Schiit Eitr that stopped working. My Retina 5K iMac has noisy USB ports so I have stopped going direct out from USB for most audio applications.

I use the DigiOne running Ropiee hard wired (ethernet) on my desktop with the ModiMulti/Vali 2+ stack. I also use an iPhone 6s+ as an endpoint and it sounds great via Apple CCK to usb into the ModiMulti (significantly less noisy than iMac). I very slightly prefer the DigiOne S/PDIF coax feed to the iPhone USB on the ModiMulti but it's closer than it should be because of the USB implementation on the ModiMulti. A static, hard wired solution is a lot more convenient on my desktop so I feel good about my Allo DigiOne purchase.

The 6s+ is the primary source/endpoint for a Bifrost 2 in a listening nook paired with an Asgard 3 and Audeze LCD-2Cs. When comparing Unison USB from the iPhone and Coax from the DigiOne on the Bifrost 2 the two sources sound virtually identical to me. Keep in mind this is based on my ears and my specific system which leans toward a warm analog sound instead of being super analytical. I listen to Rock, Pop, Electronic and Singer Songwriters so I am not trying to resolve a stage full of musicians playing Classical music.

The newer RaspberryPi 4 has a better USB implementation than the Pi3 so you might not need a HAT like the DigiOne. I'm pretty content with my sound so I didn't immediately jump on testing the new Pi as an endpoint until I read about Silent Angel VitOS for RPi4. It's a new operating software specifically for the Pi4 that strips out everything that isn't needed for a Roon endpoint. There are several discussions online about how this software takes the Pi4 up a notch sonically over USB so I decided to give it a shot. You need a case with a heat sink for the Pi4 and I had seen these very cool milled aluminum cases from Mechatronics Art. Ordered assembled with the RaspberryPi 4 the total cost was $94 - I got the orange one. You can buy a cheaper case and get the costs down to around $40 but I didn't mind spending a little extra for a nice looking case since it will be visible in my headphone rig.

Set up was a breeze. Just download the software, use Etcher to burn it to an SD card, plug everything in and turn it on. Then you scan the QR code on the Silent Angel web page and download the app which launched and immediately recognized the Pi on my network. Toggle Roon Endpoint on and restart. Easy as Pi - actually easier than most any other Pi installation with the exception of Ropiee.

Now that I'm up and running I add it to my desktop chain and try multiple configurations/comparisons starting with the ModiMulti/Vali 2+ rig switching between USB and Coax. Using LCD-2Cs and Meze Rai Solo IEM's I hear a very slight increase in highs/treble and a touch more energy. It's like splitting hairs and I would be happy with either as a permanent solution. If I was choosing today, I would probably go with the Pi4 for this rig since the Vali 2's tube in this signal path adds it's own color that sweetens the sound making it a pleasant but not super revealing system.

The Bifrost 2/Asgard 3/LCD-2C is the rig I'm most curious about how well Unison handles USB from a Pi4. I moved this rig to my desktop to compare the DigiOne Coax to the Pi4 USB. The slight high energy and treble bump is evident here as well, maybe a little more noticeable. I think I hear more air around the music if that makes sense. The differences are just that, differences - very minor ones. I actually think that if I switch to low gain, the Pi4 sounds identical to the DigiOne on high gain. Even though this is a solid state rig without a tube coloring the sound, the LCD-2Cs add their own flavor to the music. They are considered to be on the warmer/darker side but I added a C3 Copper/Silver cable to them which opened things up a bit and brings out a little more sparkle in the highs. No where close to being bright or analytical but just right for my preferences. I think that the Pi4/Silent Angel takes that up one more notch on the Bifrost 2 Unison USB in high gain. I would absolutely choose the Pi4/Silent Angel endpoint for a Schiit Unison headphone rig over a Pi with a HAT. I just don't think there's a need for the extra hardware. There are plenty of sonic tweaks to both Pi endpoints including power supply changes and cabling but the bottom line for me is that USB on the Pi4 is a great choice with Unison USB and it's about a hundred bucks cheaper than a DigiOne.