Audio-Technica AT-HA5050H

Hardware Review

Audio-Technica AT-HA5050H
Thursday, January 3, 2019
Headphone amplifier
Richard Barclay

When I reviewed Audio-Technica’s flagship open-back headphone in June last year, the ATH-ADX5000, I was mightily impressed by the Japanese audio giant’s achievement in raising the bar and creating a reference quality earspeaker that surpassed all of its previous feats. I was therefore delighted to be given the opportunity to spend considerable time with A-T’s statement headphone amplifier, the highly intriguing AT-HA5050H.

Early impressions are everything, and encountering the AT-HA5050H for the first time is sure to intrigue headphone enthusiasts perhaps more than any other amplifier presently on the market. The unit is very striking visually and its impeccable finish stands out from the crowd of minimalist, industrial stylings, as well as the more ostentatious designs that have pervaded consumer audio in recent times. Its champagne facia with laminated rosewood trim, amber-lit VU meters, contoured volume control and selector switches all hark back to a yesteryear when hi-fi systems were beautiful furniture pieces displayed in the home with pride, and listening sessions were an uninterruptible evening indulgence typically wetted with a generous snifter of brandy.

Looks can often be deceiving, and the HA5050H’s vintage vibe conceals a topology that is very much state-of-the-art, precision-engineered with a quality of components that could only be dreamed of in times gone by. ‘High end’ is an over used term, however the HA5050H is in many ways as high end a headphone amp as you are likely to find. Quality of course comes at a premium, A-T’s flagship retails for £4,500. Equipped with an excellent DAC that supports high resolution PCM and DSD bitstreams, the preamp circuit uses a pair of E88CC vacuum tubes made by JJ Electronic, while the Class A power amp circuit employs bipolar transistors made by Toshiba, all of which are selected and pair-matched after an extensive burn-in process (only those with the lowest levels of noise make the grade).

Explaining its choice of a hybrid design, Audio-Technica say the tube preamp section “adds warmth and depth to the music” while the solid state power transistors “provide powerful, distortion- free Class A amplification to drive headphones irrespective of their impedance level” - the best of both worlds, many would argue. Class A topologies have long been favoured by purists but their use has waned in recent times due to their output inefficiencies. As headphones have relatively low current demands compared to loudspeakers, it is however much easier to implement a sustainable Class A topology in a headphone amplifier. Indeed, the HA5050H draws a maximum of just 53 watts in use and runs surprisingly cool for a Class A design that incorporates vacuum tubes in its preamp circuit.

Connectivity
A total of four source inputs are provided on the rear of the unit, two analogue and two digital, selected with a toggle switch on the facia. On the analogue side there is one pair of line level single-ended RCA ins and one pair of balanced XLR ins and on the digital side there is SPDIF coax and USB. The USB input can be used in either adaptive or asynchronous mode, the latter is reported to come extremely close in performance to the SPDIF input and supports 384kHz PCM and DSD128.

 

Audio-Technica-AT-HA5050H-rear-view.jpg

 

A-T hasn’t disclosed which D/A converter is used in the 5050H, and the published images aren’t quite sharp enough to identify it, but I suspect it might be from the ESS Sabre 90xx family of delta-sigma chips. The digital board is populated with premium grade components, including the same Nichicon and Wima capacitors deployed throughout the rest of the amp, it’s also fully shielded, not only to block electromagnetic noise from the customised power transformer, but also to prevent digital noise from being picked up by the preamp tubes. A-T obviously know how to design a good DAC as the one in the 5050H sounds very fine indeed. It is highly transparent and free from glare and actually holds up surprisingly well against my current reference DAC (the £2,300 Schiit Yggdrasil) that I also connected for comparison, giving up very little in its ability to resolve with natural precision. The 5050H’s facia includes a neat grid of LEDs that make it easy to identify the sampling rate and bit depth of the audio stream being received, I enjoyed glitch-free performance with all of the PCM and DSD rates I tested using the asynchronous USB input.

The 5050H’s somewhat surprising lack of a fixed or variable line output prevents the benefits of its DAC and/or tube preamp from being shared with the rest of your hi-fi. This is a pity, as I suspect it would make an excellent front-end for a loudspeaker system and would likely broaden the amplifier’s appeal beyond earspeaker enthusiasts, reaching out to those otherwise reluctant to spend such a significant sum on a headphones-only component. It is not clear why this decision was taken, I can only speculate that making the unit ‘headphones-only’ was perhaps intended to encourage music lovers to spend more time indulging the joys of listening through ‘phones instead of loudspeakers.

Adjustable gain
With the growing divergence in headphone sensitivities, adjustable gain is becoming an increasingly important feature of headphone amplifiers. It allows easy- and hard-to-drive earspeakers to be powered from the one amplifier without the compromise of having either too high a noise floor for the former or too low an output for the latter. A-T has provided an attenuation switch on the rear panel which reduces the level of all the inputs by -12dB, equivalent to one quarter of the original input voltage, thus allowing the volume pot to be set to a higher position when using more sensitive headphones. This is important because even the best analogue pots can be subject to channel imbalances at their lowest settings and tend to perform at their best near the middle of their rotation.

The HA5050H has 14dB of gain which the -12dB attenuator effectively reduces to 2dB. These are very useful gain structures and will accommodate a wide variety of headphone designs. I am not an in-ear monitor (IEM) user but of all of the headphones I tested, most were perfectly useable with no attenuation applied. Only the Audio Technica ATH-MSR7 and Focal Utopia (both 115dB/1V SPL) benefitted from lowering the gain to release the volume pot from the first quarter of its sweep. The Audio-Technica ATH-ADX5000 (104dB/1V), Sennheiser HD600 and HD800S (both 102dB/1V SPL) and Beyerdynamic DT880 (98dB/1V SPL) all reached the desired output level between one third and one half turn of the dial without needing to engage the attenuation switch.

 

Audio-Technica-AT-HA5050H-internal.jpg

 

The volume dial itself is a feat of engineering excellence and provides a silky smooth but resistive turning action. Attention to detail is king in a top-of-the-line offering like the HA5050H and it’s these extra little touches that really upgrade the user experience to something special. The Sifam analogue VU meters are also beautifully crafted and, while some may consider them superfluous, those who enjoy visual cues I’m sure will welcome their inclusion. They indicate the dynamic range of the input signal, but are wired to the output and therefore vary with the chosen level of attenuation and position of the volume dial. If any of these settings are changed, the meters will no longer ‘dance’ within their sweet spot and you’ll need to adjust their sensitivity accordingly using the four-position toggle switch provided. I’m rather partial to hi-fi gear with output meters but I do think that, in this case, wiring the VU meters to the input instead of the output would have made more sense.

Watt quality
Compatible with headphones between 16Ω and 600Ω, the HA5050H delivers 125mW per channel into 16Ω, 62mW per channel into 32Ω, 31mW per channel into 64Ω and 3.3mW into 600Ω. In a marketplace with some seriously big hitters in the power department, the HA’s output figures may not seem all that impressive. However, it’s important to remember that most headphones require a mere fraction of the power of loudspeakers. Unless you own an earspeaker with unusually high current or voltage demands, or listen to music at ill-advised SPLs, it is likely that the 5050H will supply enough of its finest Class A power for your needs. Even with the moderately difficult to drive 600Ω Beyerdynamic DT880 I can’t say I experienced audible limitations in dynamics or low frequency extension during my auditions.

An interesting facet of this amplifier is the curious octet of 6.35mm headphone sockets countersunk into its front panel. Closer inspection reveals two mirroring groups of four headphone outputs of various impedances. This not only allows two headsets to be driven at the same time but also allows each listener to select one from a total of four output impedances - 0.1Ω, 33Ω, 82Ω and 120Ω - to achieve a preferred frequency and transient response with their particular headphone. A-T chose to implement this with four individual outputs instead of a single, switched output to preserve fidelity and avoid introducing unnecessary noise. They use Neutrik sockets that are sprung firmer than normal to provide the most reliable contact possible.

Flexible damping
As with loudspeakers, the movement of a headphone drive unit is controlled by mechanical and electrical damping, the combination of which affects its frequency and transient response. Drivers with lower nominal impedances and/or softer suspensions have less mechanical damping and require more electrical damping (i.e. a lower output impedance) from the amplifier to deliver optimal performance, while those with higher nominal impedances and/or stiffer suspensions have more mechanical damping and require less electrical damping (i.e. a higher output impedance). An appropriate level of damping is more important than many realise, it can significantly alter a headphone’s sonic presentation. The same ‘phone might sound fast, lean and analytical if it’s over-damped, or slow, smeared and bloomy when it’s under-damped. A-T summarises the relationship between output impedance and headphone performance as follows:

 

A-T-impedance-chart.jpg

 

It is uncommon for headphone manufacturers to publish output impedance recommendations for their headphones, the onus is therefore upon the listener to identify suitable pairings. Contrary to the above diagram, it is difficult to accurately predict the effect output impedance will have on a particular headphone as it depends on several measurements specific to that headphone, many of which are not typically in the public domain. The most effective method is simply to trust your ears as to what sounds best and the 5050H provides a fantastic opportunity to experiment, it soon highlights the inflexibility of a single, fixed output impedance that most other headphone amplifiers offer.

Exquisitely detailed
The HA5050H may not be the most authoritative headphone amp I’ve listened to, nor the most characterful, but it is undoubtedly the most exquisite and sophisticated. Its blend of tubes and transistors complement each other beautifully. The class A power amp delivers a composed and highly resolving presentation with satisfying extension at both ends of the spectrum, while the E88CCs provide a touch of harmonic sweetness; the combination of which makes for a mellifluous listening experience rich with natural tone, detail and depth.

Don’t however be fooled into thinking that this amplifier drapes a softening veil over the music, it can if you want it to (by increasing the output impedance), but it is intrinsically sprightly and revealing - especially through the 0.1Ω output. It just doesn’t glare or fatigue in the way that some others are inclined to in their eagerness to impress. The 5050H reproduces instrument timbres and leading edges and resolves spatlal cues with a cohesive balance that connects you to the music on an emotional level but still titillates by crisply rendering the accents and flourishes that bring performances to life. There is a particularly graceful finesse and fluidity to the upper middle and lower treble frequencies that is often absent in solid state designs, yet there is an incisive retrieval of micro-details and textures that are not always this well delineated when vacuum tubes are present. The 5050H is blessed with an understated wisdom that transforms the simple pleasure of listening into an unconsciously edifying experience.

 

Audio-Technica-AT-HA5050H-jj-tubes.jpg

Audio-Technca's tube burn-in facility

Sweeten to taste
The most responsive of the headphones I used with the 5050H’s four different output impedances was the 80Ω open-back Focal Utopia, where I found myself gravitating to the 33Ω output. This was a very seductive combination, adding the perfect amount of heft to the low end and pulling the rather bold mids back slightly to give an improved sense of distance and overall spaciousness compared to the 0.1Ω output. On the 82Ω and 120Ω configurations the Utopia’s bass became too footloose and unruly, robbing definition and attack from the mid and high frequencies. The 300Ω open-back Sennheiser HD600 and HD800S and 420Ω open-back Audio-Technica ATH-ADX5000 were splendidly composed regardless of the chosen output impedance and maintained an articulate balance through the highs and mids, but progressively relaxed and warmed through the lowest octaves at the higher settings. With these three ‘phones there was no clearly favoured ratio of damping and I found myself selecting an output impedance to compensate for the source material rather than to optimise the headset. Due to its low 35Ω nominal impedance and very flat impedance curve, the tonality of the closed-back Audio-Technica ATH-MSR7 was unaffected but its dynamics were undesirably suppressed as the output impedance increased, making the lowest 0.1Ω setting the clear winner.

Of the four options provided, I expect the 120Ω output impedance on the 5050H will be the least used in practice, since it pairs best with an earspeaker that not only has a very high nominal impedance but also a high sensitivity rating. This is because as output impedance increases, the amplifier’s power transfer efficiency decreases, i.e. the amount of current it is able to deliver to the headphone is reduced. There are comparatively few headphone designs on the market that meet both criteria (the trend has been increasing sensitivity through lowering nominal impedances). As such, I imagine that making 82Ω the maximum value and narrowing the gap between the lower settings, perhaps by including a 10Ω output, would provide finer degrees of adjustment with a broader selection of earspeakers.

Volume compensation
In a dual-listening situation in which the two headphones being used have different sensitivities or the two listeners have different level preferences, the impeded power transfer can be used as a means to control relative output levels, which is an advantage over other headphone amps that provide dual outputs but no way to adjust levels. A-T recommends the user with the less sensitive headset and/or preference for louder SPLs plugs into a lower output impedance, and the user with the more sensitive headset and/or preference for quieter SPLs plugs into a higher output impedance. While a multi-position attenuator providing fixed levels of attenuation (e.g. 0dB, -2dB, -4dB and -6dB) would provide greater flexibility, exploiting the impeded power transfer does work reasonably well and it also avoids adding complexity to the circuit design.

 

Audio-Technica-AT-HA5050H-front-view.1.jpg

 

 

Verdict
Audio-Technica’s statement tube-hybrid headphone amplifier is a remarkable feat of engineering, not least because its uncompromisingly premium design and unique suite of features set it apart from anything else currently on the market. The AT-HA5050H’s blend of tubes and class A circuitry complement each other beautifully and deliver an exquisite balance between precision and warmth, while the adjustable damping allows individual headphone performance to be optimised to taste and new sonic personalities to be revealed. Though one or two minor revisions would increase its utility even further and broaden its appeal beyond A-T’s targeted earspeaker enthusiast, in its current form the 5050H is still the ultimate indulgence in personal listening. It has certainly secured a place on my headphone amp wish list.

Ancillaries:
Source/s: Mac Mini 2010, MacBook Pro 2015
Software: Mac OS 10.11.6, Audirvana Plus 2.6.8, iTunes 12.7
Headphones: Audio-Technica ATH-ADX5000, Audio-Technica ATH-MSR7, Beyerdynamic DT880, Focal Utopia, Sennheiser HD600, Sennheiser HD800S.

Specifications: 

Type: Headphone amplifier with alternative outputs/impedances 
Preamplifier stage: vacuum tube (valve) circuit 
Power amplifier stage: Class A bipolar transistor amplifier Corresponding Headphone Impedance: 16 – 600 ohms
Maximum Output Level: 2,000 mW + 2,000 mW (16 ohms load) 1,000 mW + 1,000 mW (32 ohms load)
500 mW + 500 mW (64 ohms load), 62 mW + 62 mW (600 ohms load)

Rated Output: (20 Hz – 20 kHz): 125 mW + 125 mW (16 ohms load)
62 mW + 62 mW (32 ohms load)
31 mW + 31 mW (64 ohms load)
3.3 mW + 3.3 mW (600 ohms load)

Frequency Response (Line Input): 5 Hz – 200 kHz (0, -1 dB at 32 ohms 10 mW output)

Frequency Response (XLR Input): 5 Hz – 200 kHz (+0.5, -2 dB at 32 ohms 10 mW output)

Total Harmonic Distortion: <=0.08% (20 Hz - 20 kHz at 32 ohms 10 mW output)

Gain: 14 dB (line input); 13.5 dB (XLR input)

Signal-to-noise Ratio 104 dB (A-weighted)

Channel separation: 70 dB (1 kHz at 32 ohms)

Analogue inputs: Line input (RCA) x 2; XLR connector x 2

Digital inputs:
USB (Type B):
Asynchronous mode:
DSD128 (5.6448 MHz), DSD64 (2.8224 MHz): 24 – 32 bit
PCM 384 kHz, 352.8 kHz, 192 kHz, 176.4 kHz, 96 kHz, 88.2 kHz, 48 kHz, 44.1 kHz, 32 kHz: 16 – 32 bit
Adaptive mode:
DSD incompatible
PCM 192 kHz, 176.4 kHz, 96 kHz, 88.2 kHz, 48 kHz, 44.1 kHz, 32 kHz: 16 – 32 bit
Digital coaxial (S/PDIF) x 1
PCM 192 kHz, 176.4 kHz, 96 kHz, 88.2 kHz, 48 kHz, 44.1 kHz, 32 kHz: 16 – 24 bit

Output Connector: 6.3 mm (1/4") standard stereo jack (output impedance 0.1 ohms) × 2
6.3 mm (1/4") standard stereo jack (output impedance 33 ohms) × 2
6.3 mm (1/4") standard stereo jack (output impedance 82 ohms) × 2
6.3 mm (1/4") standard stereo jack (output impedance 120 ohms) × 2

DAC: 
Frequency response: 5 Hz – 100 kHz (0, -1.5 dB)

Total harmonic distortion: <=0.0006% (20 Hz - 20 kHz)

Signal-to-noise ratio: 113 dB (A-weighted, 1 Vrms output)

Channel separation: 110 dB (20 Hz - 20 kHz)

Input Attenuator: -12 dB

VU Meter: Range 0 dB, -10 dB, -20 dB, -30 dB

Power Supply 100 – 120V AC or 220 – 240V AC, 50/60Hz

Power Consumption: 53 W (max)

Dimensions (excluding protrusions): 100 mm (3.9") H × 332 mm (13.1") W × 327 mm (12.9") D 
Weight: 11 kg (24.3 lbs)

Price: 
£4.500
Manufacturer Details: 

Audio-Technica
www.audio-technica.com

Distributor Details: 

Audio-Technica Limited

T +44 113 277 1441
www.eu.audio-technica.com