Bob, your rec on the Gustard U12 certainly has my interest. I appreciate your obsession to detail and the fine points of what is better, this is what we depend on from you. The XMOS chip has been on my radar for a while, however it seems to be quickly upgrading in various incarnations( a good thing), so I have stood back and waited. While reading all of the recent posts RE USB recently the question came to mind, did Schiit consider the XMOS chip for the Gen 2 Bifrost board? I just PM'd Jason regarding same and he said "yes they did, and did not use it", no details, just that answer. Now I am curious why? Anyway, I am very happy with my Uber Bifrost w/Gen2. I know you are thrilled with the Gustard, everyone is happy. Wish Jason would have gone into more detail regarding their choice of chip.
Thanks for the kind words. And very good question. It may be, and I'm only guessing, they chose early on to implement the C-Media CM6631 chip - despite it's issues (no 176K sampling) - so when C-Media released the CM6631A version it was easier to use this with their board design for the GEN2. In response to ThurstonX's question on the issues with the newer CM6631A clocking I mentioned- I put up a detailed post on the Gustard U12 thread. It looks like Schiit has found a way around that problem - with a relay based DAC reset on clock changes.
“It’s a pain in the ass,” Mike said. “We’ll need a microprocessor to switch the clocks, we have to reset the DAC when sample rates change, we’ll need a hard relay mute, stuff like that.”
The XMOS has gone through several iterations - and the newest design is truly sota. - Native 32 bit 384Khz 8 X-core XMOS chip. Multi-thread. USB class 2.0 Async. And Gustard's implementation looks excellent: Separate 0.1ppm TCXO clocks, Temperature Controlled High Precision Active Crystal. One for each clocking ratio. Independent Linear Power Supply. Sealing Torodial Transformer, Multiple Sets of Multi-Level Regulation. Four outputs: Coaxial (RCA), Optical Fiber, AES/EBU, IIS (HDMI port). DSD support to 128. PCM to 384K.
I'm not saying the Schiit USB GEN2 board is not good - it is. So was my previous ref - the Musiland USB 3.0(with a Aqvox linear usb power supply). Which was better then the USB interfaces I had before like the Audiophileo 2, M2tech Evo (with custom made linear ps), John Kenny MkI and MkII,etc..
The thing that has shocked me - is how much better the Gustard U12 is. I mean not a subtle difference! The clarity and transparency has taken a big leap forward -the bass has added a half octave lower and is better defined. Sound stage bigger and more holography. Across the board better in every way. Why? How could this be? Bits are Bits right? I think it comes down to the power supply. The Gustard uses phenomenal filtering and is the first USB interface I have heard that uses AC power with a toroidal ps transformer. Not to mention the excellent clocking using TCXO 0.1ppm separate clocks. It's like some hidden distortion has been lifted - the sound is much more natural - musical - sweet - I don't really know how to discribe it properly. And other folks on the U12 thread have posted similar - including a fellow with a Peachtree that uses an on board C-Media CM6631A like the GEN 2.
But back to why the XMOS vs the C-Media - my litmus test is the $1800 Berkley Audio Design Alpha USB interface. This is a no holes barred, all out, money is no object effort to build the best USB interface on the planet. And it is fantastic! They chose the XMOS. 'Nuff said.
Here is a USB interface shootout:
http://www.computeraudiophile.com/f6-dac-digital-analog-conversion/15-universal-serial-bus-industry-standard-cables-connectors-and-communications-protocols-between-computers-and-electronic-devices-spdif-converters-shootout-15327/
The Berkley Alpha came out the winner. Do I have $1800 for a USB interface? Not even close. But if you can get close to that level of performance for $155 - well they got my money - twice (I bought two) and maybe a third for modding.
