Unfortunately, this thing has a horrible USB implementation.  90% of the time I can't even get it to connect to either my Macbook Air or my PC.  It takes a series of plugging and unplugging both power and USB from both ends, turning off and on again the computer and the DAC, and lots of stressful yelling to get it to work.  Then, 100% of the time, a Windows bluescreen ends my listening and we're back to the plugging and unplugging.  At least on the Mac it stays connected once it's connected and mostly works (a couple of dropouts here and there with Audirvana), but that's not enough for me to keep this thing.  It's too bad, because it sounds really good when it works.  
 
Maybe mine is bad.

cizx said:

  Unfortunately, this thing has a horrible USB implementation.  90% of the time I can't even get it to connect to either my Macbook Air or my PC.  It takes a series of plugging and unplugging both power and USB from both ends, turning off and on again the computer and the DAC, and lots of stressful yelling to get it to work.  Then, 100% of the time, a Windows bluescreen ends my listening and we're back to the plugging and unplugging.  At least on the Mac it stays connected once it's connected and mostly works (a couple of dropouts here and there with Audirvana), but that's not enough for me to keep this thing.  It's too bad, because it sounds really good when it works.  
 
Maybe mine is bad.

Click to expand...

Sorry for the delay in answering this. We wanted to make sure we could duplicate the issue you had.
 
First let me say that hundreds of these units have been sold without issue all over the world. What we have found with BMC is that the grounding scheme in some homes in the US can cause some issues. Power Outlet Grounding schemes in Germany are very tried and true. It is part of their safety standards. In the US this standard is very lax. Some homes dont have true grounding schemes. Especially old homes which may have had 2 prong outlets at one time and then changed to 3 prong. Ground cheaters can also cause issues. In the US only 3 reports of the issue you had have been reported. Unfortunately you and a second customer of mine after your sale had the same issue. Here is what BMC found:
 
Here a short description of what we found regarding the PureDAC's random connectivity issues:

Problem Description:
In some surroundings the PureDAC is unreliably connecting via USB.
This problem is not related to drivers and the same unit works well in most other geographic locations.

Analysis:
The hardest part of such problems is to reproduce them in a way that there is clear before and after.
We succeeded triggering the problem by using a simulated power supply and remove the noise filters. Within this condition we found very unreliable USB handshake.
We found that the noise is avoiding a complete discharge of the rather big logic power supply and the reset-sensitive XMOS USB interface fails to start-up properly.

Applied solution:
We added a discharge load to the unregulated power supply, ensuring a complete discharge within 3 sec even under noise conditions. This way the problem was resolved for a test group of 20 units.

Another issue might be excessive electrostatic discharge at the USB port, emerging from poor computer power supplies and poor grounding. We have discharge protection build in, but in some excessive cases the protection wasn't sufficient. We suggest to reduce hot-plugging. Make sure to connect your USB while both the computer and BMC is off. This issue is not a rare one. Over many years now of us selling USB Dacs, we have encounter computers shorting out USB cards on several brands we sell. The same issue can happen when you swap speaker cables from one speaker to the other while the amp is still on. Never a good idea. Computers have spoiled us with the Plug and Play nomenclature. 
 
One other issue I have run into is driver corruption. I test and play with a lot of USB devices here at Moon Audio. And after loading about 15 different DAC's and all there associated driver files I started to run into computer issues. Like the Blue Screen your are reporting. I had to wipe the computer and reinstall the operating system. Not fun when the computer is your main computer. I now have a dedicated machine just for Dac testing so when these corruptions happen there is minimal down time in reinstalling the OS.
 
Anyway BMC is on top of the issue and is implementing into the latest production batch. The fix is also easy to do on existing units in the field that become problematic. But like I said on 3 units in the US have had the issue.

Thanks for forwarding our information exchange Drew!
 
Most of this points are common for most USB DAC models.
 
I would like to add one more point you brought up:
Since Microsoft refuses to follow the USB 2.0 audio standard (unlike MacOSX and Linux) you need to install a driver for "explaining" a highres USB DAC to the operating system, so it can be used.
If you change between a lot of USB DAC for sure you will run into trouble. This is not because other DAC with XMOS USB chipsets are incompatibe, but because of build in license restricion trouble. During the installation of the TUSB driver you have to connect the DAC so it can read and confirm the PID (USB identification) and block any other DAC.
Add the fact that a clean uninstall on Windows is rather unlikely and you can look forward to the next clean install.
 
For people using a lot of DAC Mac or Linux are doing the better job, although Mac still lags behind all others concerning sound quality until there is a solution bypassing the core audio.
However a normal user won't run into such problems and can enjoy the pretty good Windows solutions without worry.
 
Hope this helps clarifying some mysteries.
 
Carlos

cizx said:

  Unfortunately, this thing has a horrible USB implementation.  90% of the time I can't even get it to connect to either my Macbook Air or my PC.  It takes a series of plugging and unplugging both power and USB from both ends, turning off and on again the computer and the DAC, and lots of stressful yelling to get it to work.
 
Maybe mine is bad.

Click to expand...

A 7 months old post but I have the same "fun" here! I bought the PureDAC one week ago and use it for my Daphile (based on Gentoo Linux, using the Squeezelite player) via USB.
 
The XMOS USB interface was one of the reasons to buy the PureDAC. My (unfortunately already sold) Matrix X-Sabre worked great with the Daphile nettop via USB. They always found each other immediately, so I am pretty disappointed about the connection trouble between the PureDAC and the nettop now. This morning, it took ages to connect the PureDAC with the Daphile nettop. Both devices were off at night. And then, when you finally see the "HR" and later the "44" sign in the PureDAC's display, it doesn't mean that it always works then! There is sometimes no sound. You have to switch off/on the PureDAC again to get the sound.
 

 Maybe mine is bad.

Click to expand...

That was my thought, too. The German B.M.C. Audio support mailed me something about a prepared update. Not sure if I can wait till it is available. Maybe my PureDAC is a 2013 model? I find the sound quality of the PureDAC amazing (and I like it as a preamp for my active speakers very much) but I need a quick USB "handshake" similar to the Matrix X-Sabre or the Oppo 105.. Also as "waf" for my gf.
 
Mario

FWIW I had similar problems with my (2013 - among the first delivered I believe) PureDAC and Mac Mini USB. I went back to optical then later re-tried after reading carefully the information in the manual.

I'm not sure exactly which suggestion solved the problem, but think a poor-quality USB cable was one part of it.

May not be the same problem as yours but in my case there have been no problems since...

argo duck said:

FWIW I had similar problems with my (2013 - among the first delivered I believe) PureDAC and Mac Mini USB. I went back to optical then later re-tried after reading carefully the information in the manual.

I'm not sure exactly which suggestion solved the problem, but think a poor-quality USB cable was one part of it.

May not be the same problem as yours but in my case there have been no problems since...

Click to expand...

I have a Nuforce Impuls USB cable. Nothing expensive but it should do its job. I wonder why my PureDAC still had this problem though the fix was already available in January.
Well, I bought the Oppo HA-1. It arrived yesterday. USB handshake works as expected.

drubrew said:

  The PureDAC drove a K1000 with excellent result. The output stage can handle more than enough current, so the maximum voltage never varies. The PureDAC has about 13Vrms at the balanced output which would result in 5W@32Ohm, or 560mW@300Ohm, or 280mW@600Ohm. This is more than enough for making your eardrums meet in the middle of your head.
 

Click to expand...

It says up to 200mA to output in user manual. So it won't deliver 5W to 32Ohms. More like 1.3W

... It sais: 13V rms even at 32 Ohms which would be 5.28W and definitely would break your headphone. A milliohm output wouldn't have any mercy with the headphone's voice coil.
For this purpose a current limiter has been implemented. In case of LEF amplifiers this implementation won't have any influence to the output impedance or any other specification.
It is just like our famous German top cars. The most brutal motorized versions anyway agreed to limit the top speed to 250 km/h for safety reasons. You will find the 250 km/h is really enough and fun on empty highways. The voluntary limitation doesn't mean anybody took away some horsepower.

Hi Carlos.
I can see the engineering viewpoint, it has to be complete product and reliable.
In car analogy, speed limiter can be removed most cases, the question whether or not is it practical depends on the specific car, in my view. 
 
For people who own ineficient planar magnetic headphones, the current limit could have been rather in 300mA region, but i have no plan to buy a planar for myself.
It is quite a bit mind boggling how good the balanced headphone out is with HD800s.  
What's more, it is sounding like 90% the same as Sennheiser's HDVA600 amp and i thought HDVA600 is one of a kind among solid state options. The liquidity and effortlessness is there with both. 
It is as if the BMC had one HDVA600 built inside. Very impressive performance indeed.
The HD800 is  hard to get sounding right and the BMC does pull it off. Really sharp attack envelopes and punchy sound across the frequency spectrum. Although it is one of the brighter DACs i have owned, it does not exaggerate HD800 brightness further. I've had dark sounding DACs that are sibbilant and this one isn't.
The amplifier topology is apparently not similar, HDVA600 is a chip amp based, although i can't find a schematic it says in datasheet (tpa6120a2) that it is a current on demand design, which would suggest some similarity.
 
If i'm not reaching into trade secrets may i ask more about the headphone stage? I'm a bit confused in how the extra current source is arranged. How does the current source 'know' when to open up? 
 
One more question. The xlr preamp out seems to be 13V rms as well. How much current can it supply?
 
Thanks.

Thanks for the very nice words!
 
The line output has a 22Ohm output impedance and can handle up to 300mA output current, which should be more than sufficient for a line output.
Generally the 13V can't be digested by any amplifier input and are rather a gain headroom for low level recordings. We had some guys that put the PureDAC level to maximum and connected it to a preamp, thinking this would be a fixed output approach and surprised about lots of distortions. For also serving those folks we implemented a "FO" (fixed out) function to the UltraDAC, which later will be also in the PureDAC.
 
By the way: for the UltraDAC we raised the current limit to 500mA already.
 
As much as I like the HD800 and the Beyers, I had my best headphone impression just recentely at the RAMF when combining a PureMedia with an UltraDAC and a Fostex TH900. I knew the TH900 must benefit a lot from a LEF amplifier but this was more than I expected.
Interestingly before the RMAF I just heard the same headphone on a show in Tokyo and didn't like it at all.

The Fostex TH900 with Silver Dragon V3 Headphone cable has been my desktop rig now for about a Year. The combo is almost flawless. We are getting back our RMAF gear today along with one of the first production UltraDac's today. Based on my impressions of the UltraDac and the TH900 at RMAF I think it might know be the Flawless combo It blew us away at the show We will start a new Thread on the UltraDac soon.

Say i would need to double my balanced outputs, is the headphone out as good a source to external units as the back end xlr line outs? 
 
Tried the Sennheiser amp line outs to monitors, but it degraded sound noticeably.
 
I have it connected right now to my hp amplifier through back end xlr-s and to my speakers from the frontal 4-pin xlr. It works, but comparative tests are a fuss so i can not have direct comparison to say which would sound better.
Technically the front has additional high current sorce, but otherwise only one gain stage, like the back xlr-s, right? Lower z in the front is due to the current source?

Hi Priidik,
 
Concerning sound quality you wouldn't have to worry. One advantage of LEF amplifiers is that the voltage output source is always small and in your case the current sources would be almost jobless.
 
The problem is the missing ground when using a 4-pin XLR connector. Unless your amplifier input is transformer coupled this could cause noise with some models. If the XLR input load is balanced against ground everything should be fine.
 
Alternately you could use Y-adapters at the line output. The output can drive a lot, so no worries here. The downside is that you can't have individual volume setting for each trunk.
 
Hope this helps!

Still loving this BMC Puredac!
 
One thing though that drives me dilly is the remote control with the reversed controls for HP and preamp section....please BMC can you fix this issue and swap out these remotes??

You know our brains are also wired in reverse right? Left-brain to right side of body; right brain to left

Luckily I can't tell my left from my right so I don't notice this idiosyncrasy of BMC's