[earfonia]

Sneak peek of a pre-production unit of Audio-Technica AT-HA5050H
 
 
 
 

 
 
 
Sections:
1. Introduction, Pros & Cons, Summary.
2. Sound Quality & Pairings.
3. Comparisons.
4. Features & Measurements.
 
 
 
I consider myself fortunate for the chance to preview a pre-production unit of Audio-Technica new flagship model of their high-end headphone amp, the AT-HA5050H. Many thanks to Audio-Technica Singapore for this precious opportunity!
 
Please take note, that the unit I review here is a pre-production unit. AT told me that they might do a further fine tuning to the product before the launch this year. So there might be some changes on the final production version. Earliest news and article I found about AT-HA5050H goes back to August 2013 when Audio-Technica exhibited AT-HA5050H in Hong Kong High-End Audio Visual Show. We can see that Audio-Technica has spent years to develop their flagship headphone amp, to really worth the position as a flagship model. And I'm glad to say, they really did marvel.
 
When writing this review, I was trying not to exaggerate too much with hyperbolic words and expressions, but it's so hard not to be emotionally expressive when describing the sound quality of AT-HA5050H, especially when it interacts deeply into the emotional realm. I'm an engineer and have tendency to use more of my left brain, to look into the technical aspects of the device I review. But when listening to AT-HA5050H, it makes me forget all the technicalities and it simply presents music in its purest form, so emotional, so involving. It doesn't matter anymore, what is its output power, maximum output voltage, output impedance, supported sampling frequencies, etc. AT-HA5050H sound quality alone makes other parameters becoming less interesting to be discussed. What I know is, all headphones I tried with AT-HA5050H perform like I never heard before with other amps, all sound beautifully musical. As if Audio-Technica gave AT-HA5050H a soul, AT-HA5050H is highly emotional and musically engaging. AT-HA5050H is all about music. Except one thing, the model name.
To Audio-Technica team: AT-HA5050H deserves a really nice & meaningful name for it like those given to some of the Audio-Technica wooden headphones. AT-HA5050H begs for a name, not merely a model number. Please give it a real good & meaningful name.
 

 
 
Before going further with details, in short, the 3 weeks experience with AT-HA5050H was truly a wonderful musical experience. Listening to AT-HA5050H was extremely addictive. It is a generator of pure musical energy to energize the soul. Simply the best DAC + Headphone Amp combo I've ever heard. AT-HA5050H sound signature is highly refined, with remarkably flat tonal balance. Silky smooth with a touch of warmness. Very rich in detail without ever sounding analytical. Very spacious and sharply focused imaging. Bass is very potent, powerful and tight. AT-HA5050H sounds powerful, with lifelike dynamic that makes all the headphone I tested sound effortless. So far, it is the best amplifier for all the headphones that I have, excellent compatibility. Not knowing the price tag, which most probably will be beyond my budget, it is not only get the full 5 stars rating for the sound quality, but AT-HA5050H to me reaches the level of "I really want it".
 

 
 
 
Pros:
Probably one of the best sounding DAC + Headphone Amplifier combo. Highly addictive and musically engaging.
 
Cons:
No Line Output from the DAC section.
 
Suggestions for improvement:
DAC Line Output, in both unbalanced RCA and balanced XLR.
Tube socket & user removable cover for easy tube replacement.
More input options such as optical SPDIF and AES/EBU input.
To position the 12 dB attenuation switch on the front panel, instead of the back panel.
To use signal compressor for the analog meters, for automatic signal attenuation, rather than manual attenuation adjustment.
 
 
 
AT-HA5050H is truly a remarkable flagship DAC + Headphone Amplifier. Top notch sound quality power house with extensive usability from easy to drive IEM up to difficult to drive headphones. Simple and intuitive design with some of the best ingredients perfectly cooked. Hopefully the final version would be even better. Kudos to Audio-Technica!
 

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[earfonia]

Sound Quality
 
 

 
 
Generally, I prefer solid state amplifiers than tube. I found many tube amps, though they have nice smooth and warm character, many are generally not transparent and spacious enough for my sonic preference. AT-HA5050H uses tubes, and my guess, from the sound characteristic; it seems to be a hybrid of tube and solid state. At the moment I couldn't get much technical information about it, so I'm just guessing here. Anyway, whether it is a hybrid or not, and whatever my preference is, I think Audio-Technica done it right. AT-HA5050H has the best of both worlds. The warm smooth and soothing characteristic of tube amp, with the speed, details, transparency, and spaciousness of solid state amp. Honestly, AT-HA5050H is the best sounding DAC+Amp combo that I've ever heard. It is true that there are many other high-end DAC+Amp combos out there that I haven't tried, but I do have some experience from many years of my audiophile journey. And IMHO, AT-HA5050H deserves the place as the Audio-Technica flagship reference DAC + Headphone Amplifier.
 
As I mentioned previously, AT-HA5050H sounds highly refined, there is no hint of harshness at all, always smooth and refined. The tubes give it some warm character, but at the right dose, and not too much. The headphone output is only slightly warmer than my Yulong DA8 headphone output. What I always afraid from a warm sounding amps is that they have the tendency to sound too mellow, sloppy, poor clarity, and congested. Well, fortunately AT-HA5050H is far from those characters. Yes, it is a warm sounding amp, but it is not mellow at all. It has very rich detail, the clarity is excellent (although not emphasized), and both are presented in a very organic and musical way, not the analytical way. AT-HA5050H is both quite revealing and yet rather forgiving. A rare combination.
 
What amazes me most is the imaging. The most spacious sounding tube amp I've ever heard. Not only that, instruments separation and spacing is very clear and focused. Very good 3D imaging, better imaging than my Mytek Stereo192-DSD and Yulong DA8 headphone output. Very lively and accurate imaging. Listening to 'Angel of Harlem' from 'Chesky The Ultimate Demonstration Disc Volume 2', this is the first time I notice and really 'feel' the main singer at the centre moving his head slightly from side to side, also sometime moving closer or away from the microphone. I got a little goose bumps when experienced it for the first time... what a shocking realistic imaging!!! I have no idea how Audio-Technica could mix all those excellent sonic characters in such a good balance.
 
Tonal balance is superb. I really like the bass, really powerful with good speed, control, and texture, and always in good balance with the rest of the spectrum. Midrange is natural warm, smooth and organic, very rich in details. Treble is silky smooth and very well extended to give good sense of transparency and airiness. I don't hear any emphasize on the tonality, from deep bass to upper treble, all are in perfect balance. From classical orchestra, to vocal and modern genres, AT-HA5050H handles them in a very good balance. Vocal is wonderfully presented in a smooth and organic way, not too warm, with good detail and texture. AT-HA5050H also has a very wide bandwidth to cover the rich spectrum of classical orchestra, with good spaciousness, airiness, and accuracy to emulate the concert hall acoustic properties. AT-HA5050H also welcomes other modern genres that ask for extra bass to bring the extra kicks and oomph.
 
Dynamic is simply lifelike. AT-HA5050H has powerful and authoritative dynamic, presented in a gentle, polite, and involving manner. Very seductive. AT-HA5050H sounds like it has tons of power reservation, and would never ran out of power. With all the headphones I used to test it, AT-HA5050H drives them effortlessly. Even the difficult to drive orthodynamic Hifiman HE5-LE, I never heard my HE5-LE sounds so effortless. Better drive than my Yulong A28 balanced headphone amp, and my Violectric HPA V200 power house. The more than 10kg AT-HA5050H really proves itself to be an impressive power house.
 
The fact is, once I started listening my music using AT-HA5050H, it usually takes hours and sometime lasted till 3-4 am. AT-HA5050H is dangerously addictive.
 
 
 
 
Headphone Pairings
 
 

 
 
AT-HA5050H has the ability to scale up most of the headphones I tried with it. My Sennheiser HD800, Beyerdynamic T1, and Hifiman HE5-LE never sounded as good before. AT-HA5050H removes all the non-ear friendly harmonics, while keeping the treble airy and transparent. It transforms the treble of those relatively bright headphones, into a silky smooth, transparent, pleasing to the ears kind of treble. Simply amazing! Beyerdynamic T1 is currently my reference working headphone, not only for music listening but also for audio mixing and editing. As with HD800, I'm often annoyed by the treble peak at around 7 kHz, and only use it occasionally for some recordings and setup that match HD800 characteristic. HE5-LE, while not having the 'reference sonic characteristic' as the T1, I really like the sound signature with some matching setup. For example, Yulong DA8 + Yulong A28, the dark and warm signature of the A28 is quite matching with HE5-LE sound signature. But HA5050H surpasses any other setups I've ever tried. HD800, T1, HE5-LE, all sound much better on HA5050H. Even the headphone output of Yulong DA8 (1000 mW class A discrete amp) that from my experience so far was one of the best amp for T1, sounds rather pale in comparison to HA5050H. HA5050H sounds more fluid and cohesive, with fuller midrange and bass. What always impresses me is the imaging, expansive soundstage with clear instruments separation & positioning.
 
AT-HA5050H is not only suitable for natural-bright headphones as mentioned above, the expansive soundstage and extended upper treble opens up warmer sounding headphones as well. Shure SRH1540, SRH840, & Philips Fidelio X1, perform admirably with AT-HA5050H. What I like from Shure SRH840 is the slightly laid back presentation with 3D imaging that I found very enjoyable. Pairing SRH840 with AT-HA5050H and listening to vocal was really an enjoyable experience. Vocal was silky smooth & detailed, with exactly the right amount of warmness, very natural and captivating. Switching to Fidelio X1, another sonic bliss! So intimate yet sounds open and spacious. Not something easy to describe. AT-HA5050H really has the magic and power to generate sonic bliss from various types of headphones. Those headphones mentioned, Shure SRH1540, SRH840, & Philips Fidelio X1, are not really warm sounding headphones, their tonality are quite natural, only relatively warmer when compared to HD800, T1, and HE5-LE.  I guess natural sounding to natural-bright headphones will get the most benefit from AT-HA5050H warm and smooth sound signature, as compared to headphones with warm tonality.
 
My new ATH-MSR7LTD also performs best with AT-HA5050H. Even when compared to AT-HA22TUBE, one of the best amplifier I have for MSR7, AT-HA5050H manage to improve the soundstage further from what AT-HA22TUBE can offer. MSR7 sounds smoother, better detail, and more spacious on AT-HA5050H. And very lively dynamic. Truly a very enjoyable setup!
 

 
 
Beside the AT-HA5050H, I also had the chance to borrow the relatively new ATH-W1000Z, the Maestoso. Rejoice the ATH-W1000X (Grandioso) fans, ATH-W1000Z (Maestoso) is IMHO an improved version of ATH-W1000X. While retaining the refined clarity of the Grandioso, the Maestoso has an improved bass! I had Grandioso for about a couple of years till I sold it a few years ago. From memory recollection of the Grandioso, the Maestoso still carries some of the Grandioso sound signature, the refined clarity and forward midrange. But Maestoso bass has been improved from Grandioso, with better overall tonal balanced. AT-HA5050H is again showing its capability to drive most headphones to their best performance. The AT-HA5050H strong bass, liquid midrange, and expansive soundstage really bring The Maestoso to its best performance.
 

 

 
 
 
 
IEM Friendly
 
 

 
 
Considering the high power output of AT-HA5050H, I'm quite surprised that noise floor of the headphone output is very low on IEM. With headphones it is totally silent, black background. But with IEM, with careful listening during silent, it is not totally silent. There is very low noise floor (hiss noise) that is simply ignorable and far from annoying. And only audible on sensitive IEMs such as DUNU DN-1000 and DN-2000. On many IEMs I tested such as UE TF10, Klipsch x10, Yamaha EPH-100, ATH-IM50 & ATH-IM70 for example, the hiss noise is almost inaudible & totally ignorable.
 
In comparison with headphone output of Mytek Stereo192-DSD, Yulong DA8, and Violectric HPA V200, at similar listening volume, top to bottom from higher to lower hiss noise:
Mytek Stereo192-DSD
Yulong DA8
Audio-Technica AT-HA5050H
Violectric HPA V200
 
AT-HA5050H headphone output has lower noise floor than the headphone output of Mytek Stereo192-DSD & Yulong DA8, at similar listening volume level, and only a very tiny bit higher than Violectric HPA V200. Quite impressive for such a power house to have such a low noise floor. Another feature that makes AT-HA5050H more IEM friendly is, Audio-Technica cleverly put a 12 dB attenuation switch to lower the overall input to the headphone amplifier. The attenuation switch doesn't seem to lower the noise floor of the output, probably only a tiny bit, but the main purpose is to widen the useful range of the volume control for IEM and other sensitive headphones. With the attenuation switch set to 0 dB, the range of volume I use for IEMs is around up to 10 o'clock. With the attenuation switch set to -12 dB, the range goes up to around 12 o'clock.
 
Multi-ways IEMs are recommended to use the 0.1 ohm output, as higher output impedance might cause a significant changes on the tonality. For example, UE TF10 sounds muffled on 33ohm output and above. The choices of higher output impedance are more for high impedance headphones.
 
The low output noise floor and the 12 dB attenuation switch make the AT-HA5050H an IEM friendly amplifier. But most important, it sounds absolutely fantastic!

 

[earfonia]

Comparisons
 
 
 
DAC Section Comparisons
 
I have a few DACs to be compared to the DAC section of HA5050H. HA5050H amplifier section will be used for the DAC comparison.
 

 

 
 
 
Mytek Stereo192-DSD balanced output to HA5050H balanced input. Interconnect: Wireworld Equinox XLR cable (DIY 40 cm cable)
 

 
 
Tonality, as you might guess, HA5050H sounds warmer and smoother than Mytek, and slightly more laid back. Mytek sounds rather more analytical when compared to HA5050H organic sound. Bass and treble extension are about the same. Mytek transient sounds faster with slightly shorter decay, while HA5050H has pleasing longer decay and sounds more organic. Mytek sounds more impactful & snappy, transient and attack are more emphasized than HA5050H, while HA5050H impact and attack are more relax, but never sound lazy either. Mytek dynamic is slightly livelier, but could be heard as slightly more aggressive as well. Mytek has slightly higher perceived detail, but with careful listening, the level of detail is actually similar. Both produce very high, realistic level of detail. HA5050H being slightly smoother with warmer presents details in a gentler manner than Mytek. For pro audio monitoring, the emphasize of detail & dynamic could be very useful to hear things clearer. But for longer period of music listening, I prefer the HA5050H dynamic presentation, lively enough but less aggressive, for less listening fatigue. But the difference is actually not much. Imaging, some might guess the warmer HA5050H would sound less spacious than the Mytek. In fact, it is not. Surprisingly HA5050H imaging is actually sounds more spacious than Mytek, presenting wider and deeper space, giving more space in between the instruments. I'm not saying Mytek sounds congested, but in comparison with HA5050H, Mytek sounds less spacious. HA5050H imaging and spaciousness is actually one of the best I've ever heard so far, and very pleasing indeed.
 
 
 
Yulong DA8 balanced output to HA5050H balanced input. Interconnect: Wireworld Equinox XLR cable (DIY 40 cm cable)
 

 
 
Yulong DA8 DAC is slightly warmer and smoother than HA5050H, with slightly thicker / fuller bass and mids. HA5050H DAC is tighter with more natural tonality. HA5050H soundstage is wider and more spacious than DA8, with clearer with better definition. While tonality is probably up to individual preference, as for imaging HA5050H is clearly the winner. Dynamic range is approximately about the same, both have quite realistic and lively dynamic. Perceived detail, HA5050H is better. The clearer instrument separation helps to increase the perceived detail as well. HA5050H headphone amplifier could be slightly too warm for Yulong DA8 DAC output. I would prefer less warm and more natural sounding headphone amplifier for Yulong DA8 to balance its warm signature. But tonality is not the game changer here, it's the superb soundstage and instrument separation of HA5050H that makes listening experience more realistic and enjoyable.
 
 
 
ifi micro iDSD unbalanced output to HA5050H unbalanced input. Interconnect: Better Cables RCA cable - Silver Serpent Anniversary Edition (6 inch)
 

 
 
I was quite surprised to hear how similar is the sound characteristic of ifi micro iDSD DAC with HA5050H DAC. Both DACs sound signatures are pretty close. I only notice slight differences between the two DACs. That makes me guessing, probably HA5050H implemented the same DAC chip as the micro iDSD, which is the PCM DAC by Burr Brown (Mytek 192-DSD implemented ESS Sabre ES9016 DAC, and Yulong DA8 the ESS Sabre ES9018). HA5050H is only slightly fuller sounding compared to micro iDSD. Spaciousness, instrument separation, detail, and dynamic, all are pretty close, with HA5050H only marginally better. Quite an impressive performance from ifi micro iDSD given the price.
 
 
If I would use pictures to compare the DAC sonic signatures, a rough, EXAGGERATED, and simplified comparison of the DAC sound signatures between the Yulong DA8, Audio-Technica AT-HA5050H, & Mytek Stereo192-DSD would be the following:
 

 

 

 
 
Yulong DA8 is warm and thick sounding, lively dynamic, but slightly lacking in definition in comparison with the rest.
AT-HA5050H is more organic sounding with better depth, spaciousness, and instrument separation.
Mytek Stereo192-DSD sounds more analytical with more impactful dynamic.
ifi micro iDSD, since the sound characteristic of the DAC section is quite similar to the DAC section of AT-HA5050H, I cannot picture their differences.
 
Please note, the above comparison is rather exaggerated for easy comparison. In reality, the differences are small, and I consider all those DACs are excellent DACs, with HA5050H is what I like most. The analytical nature of Mytek is beneficial when pairing with warm amp or headphones. Also as what it is intended, to be used by the Pros in recording or mixing studio, Mytek is expected to be more analytical to help the sound engineer to easily spots all the details in the recording. While the smooth, warm, and fuller sounding Yulong DA8 goes well with analytical amp and headphone, to make them sounds fuller and more pleasing to the ears. It is always about proper mix and match, to get the most desirable result from the available setup.
 
 
 
 
DAC+Headphone Amp Combo Comparison
 
Since all the DACs in comparison also have their own built-in headphone amplifier, I will compare them as DAC+Headphone Amp combo, and comparing the sound quality from their built-in headphone output.
 
Mytek Stereo192-DSD: No fight at all, Mytek headphone output is just a complementary of the DAC. The DAC section is Mytek main offering. While AT-HA5050H offers the headphone amplifier section as the main offering of the product. Mytek headphone output sounds rather thin and analytical in comparison to the meaty and powerful sounding AT-HA5050H headphone output. AT-HA5050H headphone output has much more bass and midrange body that give more weight and fullness to the sound.
 
Yulong DA8: From my inventory, DA8 is my favorite DAC+Amp, the best combo in my inventory, the one that sounds best for HD800 & T1. Yet DA8 headphone output (1000 mW class A discrete amp) sounds a bit pale in comparison to HA5050H. DA8 HA output is lacking the body and soul of music the AT-HA5050H has. DA8 headphone output sound signature is relatively natural with a touch of warmness, and now in comparison to HA5050H, the bass and midrange of DA8 sounds a bit thin, not as powerful and full bodied as HA5050H bass and midrange. HA5050H sounds fuller and more powerful, and has the right balance of warmness, smoothness, spaciousness, detail and dynamic.
 
ifi micro iDSD: micro iDSD HA output is brighter than both HA5050H & Yulong DA8. Quite transparent, but rather lean sounding. HA5050H sounds fuller with much better bass and midrange body. Micro iDSD headphone output sound quality is actually closer to Mytek headphone output signature, but with better implementation of the flexible power adjustment to reduce hiss noise on IEM.
 
Comparing them as one unit of DAC+HA combo, by judging the sound quality from the built-in headphone amplifier output, my preferences from best to less preferred, top to bottom:
Audio-Technica AT-HA5050H
Yulong DA8
ifi micro iDSD
Mytek Stereo192-DSD (due to higher hiss noise on IEM)
 
As a DAC+Headphone Amp combo unit, AT-HA5050H is clearly the winner hands down.
 
 
 
 
Comparison with Mytek Stereo192-DSD + Violectric HPA V200
 

 
 
Probably another interesting comparison from available setup in my inventory is to compare AT-HA5050H with Mytek Stereo192-DSD + Violectric HPA V200.
The setup:
Mytek Stereo192-DSD balanced output >> Wireworld Equinox XLR >> Violectric HPA V200 balanced input
 
AT-HA5050H once again triumph the competition hands down. Dynamic wise, the Mytek+Violectric combo can match the power and dynamic of AT-HA5050H. Level of detail retrieval also comparable, with Mytek+Violectric has slightly higher perceived clarity. But AT-HA5050H sounds much more refined, smoother, with more spacious imaging, and much clearer instrument separation. In comparison, Mytek+Violectric sounds rather rough, less refined, a bit congested, and fail to give clear instrument separation as good as AT-HA5050H. It sounds like the musicians were cramping altogether, playing in a small tight room. While AT-HA5050H gives them more space, bigger hall, and more air to breath. Mytek+Violectric combo itself is actually a very good setup, clear sounding, good detail, very powerful with lively dynamic, but rather pale in comparison to AT-HA5050H. If both are DSLR, AT-HA5050H simply has higher resolution than Mytek+Violectric combo.

 

[earfonia]

Features & Measurements
 
 

 
 
AT-HA5050H probably looks old school with left and right analog meters above the volume pot, but once we hold it (feel the 10kg weight) and listen to it, we will realize that this is a 'heavy-weight' DAC + Headphone Amp combo that has its own class. AT-HA5050H measuring at 33.1 cm wide, 34.5 cm deep, 10.0 cm high, and weigh more than 10 kg (I don't have accurate scale), is really a big and heavy DAC + headphone amplifier.
 
From the design, with only line input for the headphone amplifier without line output from the DAC, and printing on the front panel is only 'Headphone Amplifier' without any indication of the DAC section, it seems that Audio-Technica position AT-HA5050H more as a headphone amplifier rather than DAC + headphone amplifier. Or at least the headphone amplifier section is the main offering of the product, and the DAC, although very good quality, offered as complementary of the headphone amplifier.
 

 
 
The power supply is selectable, 115 VAC or 230 VAC. A small (2-3 mm) flat screwdriver is required to remove the fuse, and change the voltage when required. The fuse is timed / slow blow 2.5A - 250 VAC 20mm ceramic fuse. AT-HA5050H takes about 28 seconds to start from power ON.
 

 
 
From the top panel ventilation, we can see 2 tube transistors, JJ E88CC. In between the tubes, slightly behind them, the volume potensiometer that looks like Alps RK27.
 

 
 
At the back panel there are 4 inputs:
Balanced analog input - XLR.
Unbalanced analog input - RCA.
USB digital input - USB B socket.
SPDIF digital input - Electrical, RCA.
 

 
 
Beside the inputs, there is 12 dB attenuation switch as mentioned earlier. Also there are 2 options for USB data transfer mode, Adaptive mode and Asynchronous mode. The sonic difference between the two modes is very minimal, and quite hard to tell the difference. For consistency, in this review I used Asynchronous mode most of the time.
 
The DAC section supports all PCM sampling rates up to DXD 384 kHz, also DSD64 and DSD128. I tested all the sampling rates as well as the DSD playback, all works perfectly on this pre-production unit of AT-HA5050H. PCM performance is as good as the DSD.
 

 

 
 
The large and well damped volume knob felt solid and precise. The amount of damping is just right, not too loose, and not too tight. The large knob makes it easy to make small volume adjustment, especially when using IEM.
 

 
 
The small selector switch on the right-bottom side of the front panel is attenuator selector for the analog meters. When the music signal is too low, and meter doesn't move and stay at the minimum level, we can reduce the attenuation to make the meter moves. Likewise when the music signal is too high, and the meter stays at maximum level, we can increase the attenuation to let the meter moves within the meter range. The selector has no other function other than adjusting the analog meters. Probably fancy, but IMHO it is rather useless.
 
It is probably more useful to put a calibrated analog meters, equipped with multi stages signal compressor, rather than a manual attenuator switcher. With signal compressor, the signal to the meter will be automatically reduced when the signal is too high for the meter. No need for endless manual adjustment every time we change volume and recordings.
 
I would rather have the 12 dB attenuator switch for the amplifier input to be moved from the back panel, to the position of the analog meters attenuator selector. It is much more useful to have the 12 dB attenuator switch there, rather than the analog meters attenuator.
 
 
 
Headphone Outputs
 
The 8 headphone outputs are probably the most unique feature of AT-HA5050H. The 8 outputs are divided into 2 groups of outputs, A and B. Each group has 4 headphone outputs with different output impedance. Previously I thought there are 2 separate stereo amplifiers, one stereo amp for output group A, and another for output group B. But from my observation, it seems that there is only one stereo amplifier paralleled into 2 groups of output.
 
2 tests that I did to verify:
First, while monitoring both Left and Right channels of output B (0.1 ohms) on my digital oscilloscope, while playing mono sine wave on foobar, I slowly inserted a headphone jack on output A (0.1 ohms). During headphone jack insertion, usually, there will be a moment when the Right channel output is momentarily shorted to the ground, and will cause the output level to drop momentarily. If output A and B are driven by two separate amplifiers, momentary short circuit on output A theoretically shouldn't affect output B. I observe the Right channel of output B was affected when I slowly inserted a headphone jack on output A.
 
Setup:
Blue: Left channel of output B (0.1 ohms output).
Red: Right channel of output B (0.1 ohms output).
 

 
 
Second, load test. The headphone output has its limit of maximum output current. Under heavy load, when maximum output current reached, the output voltage of the output cannot go higher when the volume is further increased, and the output waveform will be distorted if the volume is increased beyond the output's maximum current limit. Theoretically, if output A and B are driven by two separate amplifiers, when output A is overloaded and output waveform get distorted, and output B is not overloaded, the output waveform of output B shouldn't get distorted. I observed, output B (0.1 ohms) was also get distorted when output A (0.1 ohms) was overloaded (using 15 ohms dummy load).
 
Setup:
Blue: Left channel of output A (0.1 ohms output), connected to oscilloscope input 1 and also connected to 15 ohm dummy load.
Red: Left channel of output B (0.1 ohms output), connected only to oscilloscope input 2 (1 Mohm input impedance).
 

 
 
From those 2 observations, the 2 sets of outputs seem to be driven by the same stereo amplifier. So why do we need 2 sets of output? I guess, due to the high power output of the headphone amplifier, Audio-Technica might think that the amplifier is capable to drive 2 headphones at the same time without any significant sonic degradation. And it is true. I connected 2 headphones, ATH-MSR7LTD (35 ohm) and ATH-W1000Z (43 ohm), and I didn't hear any significant sonic degradation, as compared to connecting one headphone at a time. The headphone amplifier is powerful enough to drive 2 headphones at the same time. Probably not 2 'difficult to drive' headphones at the same time, like Hifiman HE5-LE and HE6, but common easy to drive headphones and high impedance headphones, should be no problem.
 
 
Instead of using output impedance selector like on TEAC HA-501, Audio-Technica prefers to provide multiple hard wired outputs with different output impedance. Probably to avoid sound degradation from selector switch. I found the high output impedance particularly useful to reduce treble harshness, especially for high impedance headphones. But on low impedance headphones, the high impedance outputs might affect the dynamic, resulting less lively dynamic as compared to the 0.1 ohms output. During the review, I found only Sennheiser HD800 benefits from the higher output impedance, as it reduces the HD800 treble peak, but not always, depending on the recording. With other headphones, including the 600 ohms Beyerdynamic T1 that I used as main reference headphone in this review, I prefer to use the 0.1 ohms output for a tighter and livelier dynamic.
 
From simple measurement of the output impedance of each output, the average measured output impedance:
0.1 ohms output: 0.42 ohms
33 ohms output: 31.77 ohms
82 ohms output: 80.86 ohms
120 ohms output: 117.89 ohms
 
The output resistor for high impedance outputs seems to be independent for each output, not shared. That means the 33 ohm output of group A has its own output resistors, and the 33 ohm output of group B has its own dedicated output resistors. The following measurement on 33 ohms output showing that each group has their own dedicated output resistors.
 
Setup:
Blue: Left channel of output A (33 ohms output), connected to oscilloscope input 1 and also connected to 15 ohm dummy load.
Red: Left channel of output B (33 ohms output), connected only to oscilloscope input 2 (1 Mohm input impedance).
 

 
 
Output Power Measurement
Maximum output voltage of the 0.1 ohms output on 600 ohms load: 8.35 Vrms (23.61 Vp-p)
Maximum output current of the 0.1 ohms output on 15 ohms load: 356 mA (rms)
From the above maximum output voltage and current, the maximum output power of the headphone amplifier is as the following:
Max power output at 32 ohms: 2179 mW
Max power output at 50 ohms: 1394 mW
Max power output at 300 ohms: 232 mW
Max power output at 600 ohms: 116 mW
 
The >2000 mW maximum output power at 32 ohms is showing that AT-HA5050H is really a power house.
 
AT-HA5050H has no gain adjustment, and the amplifier gain is measured approximately: 4.74 or 13.5 dB gain
I found the amplifier gain setting is just right. Together with 12 dB attenuation switch, the amplifier output is suitable from easy to drive IEM up to difficult to drive orthodynamic.
 
 
 
Frequency Response
 
From a simple RMAA test using Creative Sound Blaster X7 Line Input to measure the frequency response of the AT-HA5050H (using AT-HA5050H DAC output), on 600 ohm load, the result is remarkably flat from 20 Hz to 30 kHz (+/- 0.3 dB). AT-HA5050H frequency response probably be wider than that, and the 30 kHz limit is probably the limitation of the Sound Blaster X7 line input. But I'm not sure if the 30 kHz limit is the limit of AT-HA5050H output, or the Sound Blaster X7 line input. I couldn't get official information of the AT-HA5050H headphone amplifier specification, and also Creative Sound Blaster X7 Line Input maximum frequency response. Anyway, a flat 20 Hz to 30 kHz is a remarkable specification for an audio amplifier. The slight volume imbalance shown on the graph is expected from an analog volume potensiometer, and the level of volume imbalance between the left and right channels is very small, nothing to worry about. All the outputs from 0.1 ohms to 120 ohms showing similar performance of frequency response (600 ohm load).
 

 
 
2015-02-04 Update of the Frequency Response graph
Recently I got an update from Audio-Technica for the official frequency response graph. As I expected, AT-HA5050H has flatter response with much wider high frequency coverage than the line input frequency response of my Sound Blaster X7 that I used for the RMAA test. AT-HA5050H is practically flat from 10Hz to 100kHz, remarkable!
 
Here is the correct frequency response of the AT-HA5050H:

 
 
 
Driver & Foobar setup
 

 
 
The provided ASIO driver from Audio-Technica was quite stable when used with Foobar DSD Asio proxy. Playback and moving from different sampling rate and format was smooth without any issue. But the driver was not stable with foobar WASAPI driver. When using WASAPI, the unit hang when I manually stop or pause the track, or when moving to other track. The driver compatibility with WASAPI need some fix. So for this review I used foo_dsd_asio with the following settings:
 

 
 
 
 
Once again, please take note, that this is a pre-production unit. The final production version might have some changes and improvement.  Even as pre-production unit, this unit of AT-HA5050H is a marvelous unit. The sound quality never fails to amaze me. Waiting eagerly to try the final production version later this year
 
 
 
 
Equipment used in this review:
 
Headphones:
Audio-Technica W1000Z (loan)
Audio-Technica MSR7LTD (second headphone after T1 for sound analysis)
Beyerdynamic T1 (main headphone for sound analysis)
Beyerdynamic DT880 Pro 600 ohms
Hifiman HE5-LE
Philips Fidelio X1
Sennheiser HD 800
Shure SRH1540
Shure SRH840
Yamaha HPH-200
 
IEMs:
Audio-Technica ATH-IM50
Audio-Technica ATH-IM70
DUNU DN-1000 with JVC EP-FX8M-B eartips (main IEM for sound analysis)
DUNU DN-2000
Fitear 334 universal demo unit (loan)
Fitear 335 universal demo unit (loan)
JVC HA-FXD80
Klipsch x10
Sennheiser IE800 (loan)
Shure SE846 (loan)
Ultimate Ears Triple-Fi 10
Yamaha EPH-100
 
DACs:
ifi micro iDSD
Mytek Stereo192-DSD
Yulong DA8
 
ADC:
Creative Sound Blaster X7
 
Headphone Amplifiers:
Audio-Technica AT-HA22TUBE
Violectric HPA V200
Yulong A28
 
Cables:
Pangea Audio - USB cable - PCOCC & 4% silver - 2 Meter
Wireworld Equinox XLR cable (DIY 40 cm cable)
Better Cables RCA cable - Silver Serpent Anniversary Edition (6 inch)
 
Computer & Player:
DIY Desktop PC: Gigabyte GA-H77-D3H-MVP motherboard, Intel i7-3770, 16 GB RAM, Windows 7 Home Premium 64 bit SP1.
foobar2000 v1.3.3 (ASIO Proxy 0.7.1.2)
 
 
 
Some recordings used in this review:
 

 

[schneller]

The line-in/out options seem a bit weak.
 
Can it output to an integrated amp?
 
Edit: It looks like a mini Accuphase! Very nice!

 

[earfonia]

  The line-in/out options seem a bit weak.
 
Can it output to an integrated amp?
 
Edit: It looks like a mini Accuphase! Very nice!

 
No Line Out, so cannot output to an integrated amp. But this is pre-production unit. Hopefully AT will include Line Out on the final version.

 

[r one]

really admirable review. It makes me crazy about this dac/amp ! i want it !

 

[earfonia]

really admirable review. It makes me crazy about this dac/amp ! i want it !

Thank you! I also want it

 

[audionewbi]

Anymore word on the price? It looks great and I honestly don't need a lineout. Maybe I would have prefered a stand alone amp if that would have brought the price down.

 

[earfonia]

Anymore word on the price? It looks great and I honestly don't need a lineout. Maybe I would have prefered a stand alone amp if that would have brought the price down.

AT said around 4 figures, as expected, but no confirmation yet as how much they will price it.

 

[r one]

AT HA5050 with my W3K + Balancing Act with my TH900..huuuum a taste of paradise in my room

 

[earfonia]

  AT HA5050 with my W3K + Balancing Act with my TH900..huuuum a taste of paradise in my room

 
What is that 'Balancing Act' ?
Thanks!

 

[earfonia]

Updated 8 Jan 2015 at 8:05 am:
2 pictures of the sampling rate indicator added on section 4.

 

[r one]

Balancing Act is the tube amp that i use with my Fostex TH900, made by Eddie Current 

 

 

[earfonia]

  Balancing Act is the tube amp that i use with my Fostex TH900, made by Eddie Current 

 

 
Oh wow! I just google it, that's a very nice amp