Having just completed the DAP comparison, I can refer to them a little bit to give you a better idea of the sound (although it wouldn’t be a proper comparison, since the HUD-MX1 is a desktop unit). For instance, one of the problems that I found with the Ipod Classic, is that while detail level might be comparable to the MX1, there are some distortions and digital artifacts, that you can’t get around, regardless of the amplifier you use. On the 120GB classic, for instance, the upper midrange has a certain congestion, and music never really “flows” through that frequency band. The treble also sounds a little rough, and the timbre not too accurate. The HUD-MX1 is free from those issues. Likewise, while the Teclast T51 was very smooth sounding throughout the frequency range, and it has an awesome soundstage and instrument separation, it did suffer from lack of bass punch, and the rolling off of the lower bass. Even with a mid-fi cans like the Audio Technica AD700, it’s evident that the HUD-MX1 is better from the two players I mentioned, in that it’s free from any obvious flaws or distortions. One interesting thing to note about the HUD-MX1 is that it does employ the same WM8740 Wolfson chip that’s also used on the Teclast T-51, yet the two shares absolutely nothing in common when you’re listening through both of them. The Teclast is warmer and smoother, the HUD-MX1 is much more neutral sounding.
Of course, once you are comparing the HUD-MX1 to the likes of the Hifiman HM-801, the Hifiman with the Burr-Brown PCM1704 again comes out to be in a more superior class. While I’d still describe the HUD-MX1 as a very good DAC, it still belongs in the “entry level” category, whereas no one would ever confuse the HM-801 as “entry level”. I want to make a note, however, that the HUD-MX1 is a more neutral sounding DAC than what you’d find on the HM-801, and so the HUD-MX1 might work out better for some people, depending on music preferences and what amp/cans you’ll be using with the HUD-MX1.
Talking about amps, the HUD-MX1 comes with a built in headphone ampilfier. As you can see from the photos, the front panel has two headphone jacks, a very nice feature to have, as it frees you from having to use conversion adapters. The amp might be a good extension of the DAC, and being integrated to the DAC circuit board, it certainly maintains a good level of transparency. The amp is actually just as color free as the DAC. Considering that the amplifier is sold together with the DAC for merely $179, I can say that the level of performance is amazing. Of course, if you can afford a better, separate amplifier, definitely do so. But what I mean is that the amplifier, though nothing earth shattering, does perform a very respectable job. I’ve been listening through it with a variety of cans including the UM Mage, the Audio Technica AD700, AIAIAI Tracks, Sennheiser PX100-II, Superlux 668B, and even the HD800. With the super-sensitive UM Mage, noise is almost non-existent until you go past the 3 o’clock level. With the high gain mode turned on, it can drive the HD800 to really loud level.
Although I would regard the HUD-MX1 more as a stand alone DAC, and the amplifier being an added feature. But still, it’s good that Audinst is including the headphone out in the package. The default National Semiconductor LME49860 opamp that’s positioned at the output of the D/A chip is socketed, and if you wish to optimize the sound quality of the headphone out, you can try to roll opamps.
The final opamp before the headphone out is an AD8397 (SMD type), and though it’s a fairly difficult opamp to implement in a circuit, it has a fairly powerful output of 310 mA into 32 Ω.