The FFT of the SDAC with a 10kHz stimulus is primarily for seeing clock jitter artifacts and other non-harmonically related spurs. It is not very useful (for the reasons you mention above) for analyzing harmonic distortion components. We will publish a 1kHz FFT soon!

Hi All, I thought I would provide some technical details about the SDAC design that are not evident by reading the specifications. I posted this on the Massdrop discussion as well... When we were approached to design a USB DAC that could provide equal or better performance than the other DACs...

Hi m8oman, The m905 headphone amplifier is very similar to the m9XX.  We actually started with the m905 circuitry when beginning the m9XX development. But given that the m9XX comes with size, power, and cost constraints we had to strip things down a bit. The main things that changed are as...

Hi all, We burn in all products (including the new m9XX) for a *minimum* of 24 hours.  Typical burn in is 48 hours.  Then each unit gets a complete bench test and final inspection. Lastly, before the unit is sent to pack-out, gets a complete listening test. All of these tests are logged on a...

We tested the m9XX with Ubuntu 12.04 today and it worked perfectly. This is the only "modern" linux box we have in the shop right now.  We will report any other distributions that we can verify work with the m9XX -Michael

I just discovered a typo in a document we sent out to the reviewers and Massdrop: The amplifier in the m9XX is incorrectly indicated at the THS6072.  The correct number is THS6012! Big difference... -Michael

"90" is unity gain in the attenuator and unity gain on output amplifiers. "90." is +10dB gain in output amplifiers and -9.5dB on attenuator.

Hi m8o, The curve you see on the power output vs load impedance is created by the interaction of several factors. 1. m9XX power supply is current limited to .52A when in buss powered mode and 1.6A when in High Power mode. 2. The m9XX uses a linear output amplifier.  A theoretically perfect...

By the way, the attenuator step size is 0.5dB.  The display indicates the half-dB settings by illuminating the decimal point.

Setting the volume at 90 will result in the DAC running at full scale (with the attenuator at 0) and a 2Vrms output for a 0dBFS signal.  This is the top of the low gain range.  This would be the optimal setting for using the m9XX as a fixed DAC.

Hi XERO1, The m9XX attenuator is a hybrid design. Most of the volume control duties are handled in the digital domain with 32 bit processing but there are two analog gain ranges. This allows a full 98dB of volume control range, preserves a very low noise floor for IEMs, and allows high peak...

Hi Dave, The circuitry in the m920 was developed primarily while listening to HD600s, HD700s and HD800s.  The m920 is very will suited for these phones and will certainly bring the best out of your HD650s.    The volume control of the m920 is capable of precision attenuation over a 96dB range...

We did find and correct the problem with the popping sound when the m920 switches from DSD 128x to PCM.  As well we have been working on pinning down a few issues with newer Macintosh computers with USB3 ports.  While I know it can be frustrating living with this inconvenience testing a new...

phunge, The old m902 or m903 remotes work fine with the m903.  The the codes are the same but the m903 remote has the push-hold features printed on it. The fixed DAC output feature is only for the unbalanced outputs.  However, the balanced outputs can be set to any preset level so that they...

The headphone outputs are 1/4" TRS.  It is unbalanced but you wouldn't want to plug in an 1/4" TS plug or you would short the right output to ground.  Can I ask why you would want this? Michael

Hi ungo, The reason for the connector choices is largely panel space requirements.  There is a large number of input and output options on the m9xx series and the balanced input is used more frequently in the professional world.  That is why there is an XLR input rather than output.

Any m920 purchased will have the minimum phase filter.  The small number of units that went to dealers without this feature are being returned to the factory.  No units will be sold to customers without this feature! That said, there will be a minor delay in getting the new units to the...

All m920s available to purchase will have the minimum phase filter.

The top and bottom plates are machined, brushed, and anodized aluminum. Very similar to MacBooks  The front/side panel is brushed stainless steel and the rear panel is nickel plated aluminum.

Both will require updating.

The units that went will need a hardware modification to enable the minimum phase filter.  Unfortunately they will need to come back to Colorado for that.

Hi All, I thought I would chime in here and describe some of what is new inside the m920. As you can see the chassis is pretty much the same as the m903 but with a new color scheme and an additional LED to indicate the presence of a DSD stream.  The technology inside however is the result of a...

Quote: I'll preface this by stating that I have not converted one of our headphone amps to a four wire connection and listened... But, my guess is that the crosstalk induced by that small portion of common ground is negligible.  Personally I prefer to listen to headphones with some sort...

Hi All, This is a very interesting thread with lots of good discussion.  A few thoughts came to my mind while reading.  I know this is a bit of a tangent to the original topic... In my opinion there should be no inherent difference between the sound qualities of unbalanced and balanced...

In my view there is no performance advantage to using an external USB-SPDF converter.  I think it could only detract from the performance of the built in USB system.  When using the m903 USB input (or any asynchronous mode USB DAC for that matter) the m903 is the clock master and the computer...