Audio-Technica AT-HA22TUBE In-Depth Review
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earfonia

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It was during last year (2014) Audio-Technica event in Singapore, that I had the opportunity to audition the AT-HA22TUBE headphone amplifier. Tested it with a few headphones, I was quite impressed with the sound signature. Few months later, I get a unit for myself. I've started drafting this review many months back, and it has been delayed due to unforeseen tight schedules. Glad that I finally manage to post the review of this wonderful small desktop tube amplifier.
 
http://www.audio-technica.com.sg/products/amplifiers/at-ha22tube
 
 
 

 

Review sections:

Introduction, Pros & Cons, Suggestions for improvements
Sound Quality
Comparisons
Features & Measurements
Tube Rolling
 
 
 

 
 

 
AT-HA22TUBE is a small desktop hybrid headphone amplifier. The gain stage is using modern tube, JJ E88CC, and solid state power transistors are used for the output stage. This configuration is aimed to combine the rich & smooth tube signature with the drive ability and transparency of solid state transistor, to get the best of both worlds. The tube is on socket, therefore can be easily replaced by other compatible E88CC / 6922 tube transistors.
 
The following is a nice Audio-Technica advertisement video (in Japanese). The video shows the circuit board of the AT-HA22TUBE. All discrete components without any Op-Amp.
 
https://www.youtube.com/watch?v=-XRdnHldMEs
 
 

 
The case is solid and well made, made of aluminium alloy with die-cast front panel. On top, die cast tube cover is to protect the tubes, which can be removed for tube replacement. Overall build quality is solid and very good.
 
 

 
Before getting into details here are some points of Pros, Cons, and some suggestions for improvement.
 
 
[size=17.03px]Pros:[/size]
Great sound quality. Neutral, lively & musical sounding.
Rollable tube.
Earphone friendly -12 dB attenuation feature.
 
 
[size=17.03px]Cons:[/size]
Amplifier casing doesn't seem to be properly grounded and headphone output may get EMI noise when the amplifier is placed in close proximity to EMI transmitting devices such as cordless DECT phone.
 
 
[size=17.03px]Suggestions for improvements:[/size]
Improve power supply with properly grounded power supply and casing to improve EMI immunity.
Higher output power.
 
 
 
 
 

Sound Quality

 
The sound signature described here is based on the stock tube JJ E88CC. DACs that I used most for this review are ifi micro iDSD and LH Geek Pulse XFi. As for headphones, ATH-MSR7LTD, Beyerdynamic T1, and Sennheiser HD800 are my references for sound signature evaluation. I used other headphones and IEMs as well, but those three are the main headphones for evaluation.
 
 

 
Neutral, smooth, and spacious is how I perceived the AT-HA22TUBE sound signature. AT-HA22TUBE is not the type of tube amplifier with very warm and mellow sound signature. It doesn't really sound tubish from tube amp perspective. In fact, AT-HA22TUBE is quite a transparent and neutral sounding tube amplifier, but not at the transparency level of an analytical sounding solid state amplifier. It has mild tube warmness and richness, effective enough to smoothen edgy treble without giving too much colouration or sacrificing details. It has the combination of smoothness of a tube amp and transparency of a solid state amp in a nice proportion. AT-HA22TUBE let me hear the characteristic of the various DAC output quite easily, which is a sign of a good headphone amplifier. While it does has tube flavour in its signature, but it does it in a transparent way, and still reveals the character of the source quite clearly.
 
 

 
Bass sounds full with good weight and punch, but the speed is around average. Not very fast but not slow either. When the tube replaced to Genalex Gold Lion E88CC, bass tightness and speed improves slightly. Midrange is mildly warm and smooth with good tonal density. And the treble is smooth and transparent. Transient and dynamic are good. Though I don't consider the AT-HA22TUBE as super-fast and punchy, but I never felt the dynamic is lazy or lacking speed. It is quite lively sounding with good dynamic. Decay sounds quite natural, and a tad longer, less dry than my Violectric HPA V200 which sounds a little dry in comparison. Perceived level of detail is very good, realistic enough without being over emphasized. But it is clearly not an analytical sounding amplifier.
 
What I like most is the level of holographic imaging and spaciousness that beats my Violectric HPA V200 desktop amplifier that cost a few times AT-HA22TUBE. And that alone speaks a lot of how good this little tube amp is. For those looking for a tube amp with strong tube flavour, AT-HA22TUBE might not be the right choice, at least with the stock tube. Though AT-HA22TUBE may have stronger tube flavour with different tube, the stock tube only gives mild tube flavour, which is actually just nice to make AT-HA22TUBE a good all-rounder amp, which goes well with wide variety of headphones and recording genres. AT-HA22TUBE sound signature matches quite well with my personal preference and after using it for almost a year; I honestly like it a lot. I do wish the bass could be tightened a little bit, I'm a fan of fast and tight bass, but for the price there is nothing to be complained of. The bass is fast and tight enough to make me toe tapping.
 
 

 
I find AT-HA22TUBE matches easily with many headphones and IEMs, but especially good with neutral to bright sounding ones like ATH-MSR7/LTD, Beyerdynamic T1, and Sennheiser HD800. ATH-W1000Z was also sounded very good and enjoyable with AT-HA22TUBE when I reviewed it a while ago. As for IEMs, I really like how my DUNU DN-1000, DN-2000, DN-2000J and 1964 Ears V3 sound when paired with AT-HA22TUBE. I can hear a soft hiss noise on 1964 Ears V3, but hiss noise on IEM Is pretty low and at acceptable level. No audible hiss noise on dynamic drive IEMs that I tried. Especially for DN-2000J, so far I haven't found better amp or DAPs in my collection that matches DN-2000J better than AT-HA22TUBE. AT-HA22TUBE is simply a very musical and enjoyable little desktop tube amplifier.
 
 
 
 
Personally I'm not a great fan of tube amplifiers with strong tube flavour, or those that sounding too warm and mellow. I prefer fast, detailed, and dynamic sounding amplifier with spacious holographic imaging, that doesn't sound harsh or analytical. AT-HA22TUBE being a hybrid amplifier is surprisingly has the sound signature that is pretty close to my personal preference. For the price, it is a steal! Kudos Audio-Technica!
 
 

 
 
 
 
 

Comparisons

 
 

Comparison with ifi micro iCAN, and iCAN+iTUBE combo

 
 

 
I really like both, and though both have different topology, solid state and hybrid, the difference is not night and day, and they are both transparent with natural tonality.
 
Refined, smooth, transparent & spacious sounding is how I perceived iCAN sound signature. Bass is leaner than AT-HA22TUBE, and overall tonality lean a little towards analytic. iCAN sounds more transparent and spacious than AT-HA22TUBE. What I like most from iCAN are the decay that sounds very natural to my ears, and the spacious soundstage. iCAN is one of the most neutral sounding solid state amplifier that I have. It has excellent detail retrieval, yet always sounds smooth and refined without any harshness.
 
AT-HA22TUBE, as expected from a tube amp, is slightly smoother with fuller midrange and bass than iCAN. Being a tube amp, as mentioned earlier, AT-HA22TUBE is quite transparent sounding as well, with minimum tube coloration (using stock tube JJ E88CC), only a touch warm, and sounds more like a smooth and full bodied solid state amp. Bass has more oomph on HA22TUBE, and it helps to improve musical engagement. It never shies in revealing detail, and pretty close to iCAN in detail retrieval. For neutral to bright sounding headphones, AT-HA22TUBE is my preferred amp, while for a warmer headphones such as ATH-R70x and Shure SRH1540, iCAN matches them better.
 
So, does HA22TUBE is equal to iCAN + iTUBE? Not really. iCAN+iTUBE combo in my opinion is still a little better, slightly more refined, and better in holographic imaging and spaciousness. iCAN+iTUBE manage to integrate the best of both worlds, the transparent and detail character of solid state with smooth warm character of tube in a very musical way. Though AT-HA22TUBE also has that characteristic, iCAN+iTUBE combo is slightly better. But iCAN+iTUBE cost more than double the price of AT-HA22TUBE. So value wise, I would say AT-HA22TUBE competes well with iCAN+iTUBE combo.
 
 
 

Comparison with Violectric HPA V200

 
 

 
Violectric HPA V200 has tighter and punchier bass, with more power and authority. While AT-HA22TUBE bass is slightly less tight and punchy as the V200, but doesn't sound slow either, and for some recordings actually AT-HA22TUBE bass sounds fuller with more oomph to it. V200 sounds a little dryer with faster decay, and slightly more congested with narrower stereo imaging. AT-HA22TUBE has a more relax decay that somehow to me sounds more natural and pleasing. AT-HA22TUBE has wider and more spacious holographic imaging. When listening to the 'Dancing Flute & Drum' track from the 'Dr. Chesky's Sensational, Fantastic, and Simply Amazing Binaural Sound Show' album, AT-HA22TUBE performs better than V200 in creating the realistic sensation of being in the hall. V200 makes the hall somehow sounds damped and dryer, while AT-HA22TUBE renders the room acoustic in a much more realistic way, more spacious holographic imaging with a more natural sounding hall reverberation.
 
HPA V200 is a power horse. When driving my Hifiman HE-6 orthodynamic headphone, there is no contest here, HPA V200 with many times more powerful output than AT-HA22TUBE trumps easily. But when driving easy to drive headphones, even my reference high impedance headphones such as Beyerdynamic T1 and Sennheiser HD800, I find myself liking the AT-HA22TUBE better than HPA V200. For easy to drive headphones, AT-HA22TUBE is highly recommended.
 
 
 

Comparison with Geek Pulse XFi headphone output

Geek Pulse XFi headphone output has a clean, smooth, and transparent character, very good detail without sounding analytical. Compared to AT-HA22TUBE, Geek Pulse XFi headphone output sounds a little more detailed and transparent with a little faster transient and attack. While AT-HA22TUBE sounds a tad fuller on the midrange, a little warmer, and a tad smoother treble. Both have very good holographic imaging, wide and spacious, with AT-HA22TUBE wins by a very slight margin in imaging department. Besides being a little different in sound signature, IMHO both are equally good. Considering the high output power of Geek Pulse headphone output that is higher than AT-HA22TUBE output power, does AT-HA22TUBE adding any value to Geek Pulse XFi? Yes. Not for the power, but for the sound signature. AT-HA22TUBE with mild tube touch and richer sounding midrange is actually a very nice compliment to Geek Pulse XFi, especially on vocal.
 
 
 
 
 

Features & Measurement

 

12 dB Attenuation Switch

Besides the convenient 3.5mm and ¼” socket on the front panel, 12 dB attenuation switch is a nice feature of AT-HA22TUBE. Instead of changing amplifier gain, AT cleverly include 12 dB attenuator switch for IEM / earphones use, to have wider range of usable volume.
 
My listening volume with my DUNU Hybrids, the DN-1000, DN-2000, and DN-2000J are around 80 mV, or can be a little higher depending on recordings. So my volume reference for IEM is 100 mV for easy reference. Without the 12 dB attenuation, volume knob position for 100 mV output is at around 8:45’ am. With the 12 dB attenuation, the volume knob position is at around 10:00’ am. That means wider volume range for IEM.
 
 
 
 

[size=17.03px]Line Output Bypass[/size]
The pair of RCA line output is a simple bypass from the RCA line input, not a pre-amplifier output from the tube stage. The idea is that it may be used for bypassing the source to another amplifier, for example a speaker amplifier or a receiver.
 
 
[size=17.03px]Power Adapter[/size]
Power adapter is unfortunately not using the common 5.5mm DC connector, but a 6.0 mm DC connector that looks like HP laptop power adapter DC connector. This makes it a little difficult to use other 15 VDC power adapter.
 
 

 
A small note, my AT-HA22TUBE power adapter was faulty after about 7 months of use, then I got the replacement from Audio-Technica Singapore. Hopefully this one will last.
 
 
 
[size=17.03px]Noise[/size]
Off-On switch popping noise sounds soft on AT-HA22TUBE. It doesn't mean that the popping noise is very low in level, but because the popping sound frequency is low and it doesn't sound annoying. The level of popping noise is actually around moderate level, more or less similar to my other desktop equipment, such as Geek Pulse, Geek Pulse XFi, Mytek Stereo192-DSD, Yulong DA8, and Yulong A28. High impedance headphones are less affected by the Off-On popping noise, but for sensitive IEMs it is recommended to unplug the IEM from the amplifier before switching On or Off.
 
Recording the Off-On-Off popping noise to be compared with other DACs and amplifiers.

 
On my oscilloscope, noise floor of the headphone output when playing silent track (volume was set to 100 mV rms at 0 dBFS 100 Hz sine wave) is only around 2.5 mV rms, and less than 3 mV. It is generally very low, and only audible on very sensitive IEMs. During measurement, the base noise floor of my oscilloscope without any input is already around 1.8 mV, so the additional noise from AT-HA22TUBE is practically around 1 mV which is very low. But measured noise is not always correlate to perceived hiss noise, depending on the harmonic frequency of the noise. 
 
 

 
When volume is set to 100 mV rms output when playing full 0 dBFS sine wave, and then playing silent track, AT-HA22TUBE perceived hiss noise is approximately the same as my desktop amp Yulong A28 ('High' unbalanced output), Geek Pulse, and Geek Pulse XFi headphone output (tested using 1964 Ears V3). The perceived hiss noise is lower than Yulong DA8 and Mytek Stereo192-DSD headphone output, but higher than Violectric HPA V200. Simplified comparison of perceived hiss noise, from highest to lowest, top to bottom:
 
Mytek Stereo192-DSD
Yulong Sabre DA8
AT-HA22TUBE (connected to ifi micro iDSD line output)
Violectric HPA V200
 
Practically noise floor is not audible on all headphones that I tried with AT-HA22TUBE, only audible when using very sensitive IEM such as 1964 Ears V. Even with sensitive IEMs like my collection of DUNU hybrids I find the mild hiss noise is still acceptable and practically quite ignore-able when the music is playing. Generally no perceived hiss noise on dynamic driver IEMs. Therefore I still consider AT-HA22TUBE to be an IEM friendly headphone amplifier.
 
Here is the 100 mV rms Sine waves on oscilloscope that look pretty clean.
 
0 dB attenuation
 
12 dB attenuation
 

 
Compared to Geek Pulse XFi headphone output at low gain that looks bit noisy on oscilloscope (Oscilloscope bandwidth reduced to 20 MHz for this measurement), but the noise is actually more on high frequency noise that is not audible, so perceived hiss noise is actually very low:
 
 

 
 
[size=17.03px]Maximum Output Voltage and Power[/size]
 
AT-HA22TUBE is not in the category of high output power headphone amplifier, but output power is certainly sufficient for most headphones from low to high impedance, though might not be high enough for difficult to drive headphones like some Hifiman Orthodynamic. I’ve used it to drive my 600 ohms Beyerdynamic T1, and AT-HA22TUBE has enough output voltage to drive T1 to a pretty loud listening level for most recordings. Only for some recordings with very high dynamic range like those from ‘Dr. Chesky's Sensational, Fantastic, and Simply Amazing Binaural Sound Show’ album, I have to turn the volume to maximum to get my listening level.
 
Maximum output voltage at 600 ohms is around 3.1 V (rms). While most of my desktop DACs headphone output are maxed at around > 6 V. My normal listening level for common modern recordings on 600 ohms Beyerdynamic T1 is at around 1.25 V. But for Chesky binaural albums sometime may go up to around 4 V, depending on the recording. So 3.1 V is generally sufficient, but may not be loud enough for some recording to drive 600 ohms Beyerdynamic T1. 6 V (rms) maximum output is actually preferable for some high impedance headphones. Looking at the AT-HA22TUBE specification, it only specified the of output power for up to 300 ohms. So I guess up to 300 ohms is the recommended headphone impedance for AT-HA22TUBE.
 
When measuring output power on for the low impedance, I did it many times, but I couldn’t get the measurement value that close to AT-HA22TUBE advertised specification. Until I realized that Audio-Technica was using different convention for advertising the output power. Generally maximum output power at 1% total harmonic distortion (THD) is the general convention, but AT uses 10% THD convention.
 
Audio-Technica advertised specification for the output power:
 
(10% at the time of 16Ω, THD) 500mW +500 mW 
(10% at the time of 32Ω, THD) 300mW +300 mW 
(10% at the time of 64Ω, THD) 150mW +150 mW 
(10% at the time of 150Ω, THD) 60mW +60 mW 
(10% at the time of 300Ω, THD) 30mW +30 mW
 
I don’t have audio analyser to accurately measure the output THD at high output, but I use my own method that so far have produced result that is quite close to the advertised output power by other companies that use the 1% THD convention.
 
In my method, I use the FFT feature on my oscilloscope to observe the increase of THD while increasing the volume. 40 dB is set as the margin between the main frequency and the harmonic distortion. I use 40 dB to represent percentage as it is equivalent to 100x. That means, maximum output power is measured when harmonic distortion is almost exceeding the -40 dB threshold from the main frequency. Besides observing the harmonic distortion, sine wave shape is also observed to make sure that there is no obvious visible distortion on the waveform when maximum power reading is taken. 20 Hz sine wave is used for the measurement for the reason that 20 Hz is testing the amplifier power supply, to supply enough current to complete the 20 Hz cycle. Some amplifier with poor power supply design may produce perfect since wave at higher frequency, at high voltage output, but at the same volume fail to produce perfect 20 Hz sine wave due to the lack of current supply from the power supply. So, 40 dB harmonic distortion thresholds using 20 Hz sine wave is currently my method for estimating the output power of an amplifier. As for the load, 15 ohms resistor is used for maximum current measurement.
 
 
 

 
From my measurement:
Maximum output voltage at 600 ohms load, at 0 dB attenuation: 3.12 Vrms
Maximum output voltage at 600 ohms load, with -12 dB attenuation switch: 1.56 Vrms
Maximum output voltage at 33 ohms load, at 0 dB attenuation: 2.66 Vrms
Maximum output voltage at 15 ohms load, at 0 dB attenuation: 2.27 Vrms
Calculated maximum output current at 15 ohms load: 151 mA
 
Calculated estimated power output:
At 15 ohms load: ≈ 340 mW
At 33 ohms load: ≈ 214 mW
At 300 ohms load: ≈ 32 mW
At 600 ohms load: ≈ 16 mW
 
 
 

 
[size=17.03px]Operating Temperature[/size]
As expected from a tube amp, it gets quite warm after a while, but still within reasonable operating temperature, even in a warm tropical climate like here in Singapore. In around 31 degree Celsius room temperature (no air conditioning), I once monitored the operating temperature in the area between the tubes, it reached around 46 degree Celsius at the maximum reading.
 
 
 
[size=17.03px]Output Impedance[/size]
At around 2.29 ohms, output impedance of the headphone output is low, and shouldn’t be causing any audible inconsistent frequency response on multi-ways IEM such as multi BA drivers IEMs. From my experience, below 5 ohms, output impedance of a headphone amplifier can be considered low and acceptable.
 
 
 
[size=17.03px]Channels Volume Balanced[/size]
Measured volume channels balance throughout the volume range is within 0.5 dB which is good. No audible volume imbalance issue so far.
 
After some reading, generally the convention for analogue stereo volume control is as the following:
Very good channels balance: ≤ 0.3 dB
Good channels balance: ≤ 1.0 dB
Not good channels balance: > 1.0 dB
 
Here is my measurement on some point of the volume throughout the range:
 ​
Brand / Model
Vol. Position
HP Output (Vpp)
Imbalanced
(dB)
Left
Right
Audio-Technica
ATH-HA22TUBE
Headphone Out
0 dB Attenuation
600 ohms load
08:00' (50 mV rms)
0.162
0.162
0.00
08:45' (100 mV rms)
0.304
0.292
0.35
09:15' (200 mV rms)
0.584
0.556
0.43
10:30' (500 mV rms)
1.432
1.456
-0.14
12:00' (1 V rms)
2.840
2.820
0.06
14:00' (2 V rms)
5.720
5.400
0.50
14:30' (2.9 V rms)
8.400
8.160
0.25
Max 17:00' (Distorted)
-
-
-
Audio-Technica
ATH-HA22TUBE
Headphone Out
12 dB Attenuation
600 ohms load
09:15' (50 mV rms)
0.160
0.156
0.22
10:00' (100 mV rms)
0.302
0.304
-0.06
11:30' (200 mV rms)
0.584
0.580
0.06
13:30' (500 mV rms)
1.440
1.360
0.50
15:15' (1 V rms)
2.840
2.760
0.25
Max 17:00' (1.44 V rms)
4.160
4.120
0.08

 
 
 
 
[size=17.03px]Frequency Response[/size]
The specified frequency response for AT-HA22TUBE is: 10Hz ~ 100kHz (-3dB)
I don’t have audio analyser to measure the full frequency response. RMAA test using HRT LineStreamer+ ADC with 24/96 resolution which only covers the audio band, is only for verification purpose of the frequency response within the audio band frequency. As you can see, using the ifi micro iDSD as DAC, the result is a very flat frequency response up to 30 kHz (in comparison to ifi micro iDSD Line Output).
 
 

 
 
 
 

Tube Rolling

 
 

 
I’m not a tube expert and don't have much experience with tube. In the past I had some less than impressive experiences with tube amps, and was not a tube fan. But since last year, I started to have some good experiences with good tube amps, and started to like them.
 
I did some reading and ask a friend who is a tube expert, for some recommendation, and bought another 2 pairs of 6922 / E88CC tubes for tube rolling. The 2 pairs are not cheap and cost almost as much as the AT-HA22TUBE. One pair is NOS (New Old Stock) of Amperex PQ, made in 1969 by Philips USA, bought from a friend, a tube collector. The other pair is modern tube, Genalex GOLD LION E88CC, bought from Upscale Audio, and I chose the platinum grade pair. For a more in-depth review of 6922 / E88CC tubes, I highly recommend reading the excellent 6922 Tube Review by @rb2013 here:
http://www.head-fi.org/t/761078/6922-tube-review-17-top-6922-6n23p-e88cc-cca-7308-e188cc-tubes
 
The sound impression of the stock tube JJ E88CC has been elaborated earlier, so the following is the sound impression for the other 2 tubes, the Amperex PQ and Genalex GOLD LION. Tube rolling is not as easy as Op-Amp rolling, because I have to wait until the tube cool down before removing it from the socket. And then wait for a few minutes till the installed tubes warm up before starting the test. So please read the following tube impressions with a grain of salt.
 
 
 
[size=17.03px]Genalex GOLD LION E88CC[/size]
 
 

 
The Genalex GOLD LION sounds full and powerful, slightly thicker tonal density on the midrange and bass, and sounds really nice for the three reference headphones that I used, which are ATH-MSR7LTD, Beyerdynamic T1, and Sennheiser HD800. Bass is tighter and fuller. Treble is smoother and a tad softer on Genalex GOLD LION, therefore it is perceived as a tad darker than the stock JJ tube. Just a tad. Vocal sounds fuller on Genalex GOLD LION. Midrange is very rich and smooth, but not really warm. Genalex has good speed and detail. Clarity is more or less similar to JJ, better than Amperex PQ.
 
Holographic imaging is slightly less expansive on Genalex GOLD LION as compared to JJ E88CC, and presentation is more intimate. Imaging is still quite spacious and accurate, slightly better than HPA V200 amp, but not as wide and spacious as the JJ E88CC. Genalex GOLD LION is preferable for slightly more intense tube coloration, fuller, thicker, and more intimate sound signature without sacrificing clarity or sounding too warm and mellow.
 
For bright headphones, in my opinion, Genalex GOLD LION is a better choice than the stock tube. It is now my favourite tube for AT-HA22TUBE.
 
 
 
[size=17.03px]Amperex PQ 6922[/size]
 
 
 

 
The most ‘tubish’ sounding among the three, with warmer and mellower sound signature. Amperex PQ sounds relax and a tad slower than JJ and Genalex. Bass is not as fast and powerful as Genalex, but still with pretty good speed and tightness. Treble is less transparent and softer when compared to both JJ and Genalex, but silky smooth and very effective in removing any treble harshness. Amperex PQ tonality could be perceived as slightly midrange centric when compared to the stock tubes. Midrange sweetness for vocal, which is difficult to be described, is possibly the strength of Amperex PQ. Vocal presentation is forward, smooth, warm and very intimate. Tube lover who is looking classic tube flavour would most probably love the Amperex PQ sound signature.
 
Holographic imaging is less spacious and not as holographic as the JJ and Genalex. JJ with its expansive imaging is still the winner in this department. Detail and clarity are also slightly less when compared to the modern tubes, JJ and Genalex.
 
What a little annoying is that Amperex PQ is prone to microphonic. From a gentle knock on the amp casing, or when unplugging the headphone jack, I can hear some microphonic noise from the tube. Microphonic tube could be a problem on speaker system as the whole system vibrates when music is playing, but not really an issue for headphone amplifier.
 
 
 
All the 3 different tubes are excellent tubes with their own enjoyable and unique sound signature. Personally I prefer the more lively presentation of the modern tubes, JJ and Genalex. The following are the simplified summary of the three:
 
JJ E88CC:
Excellent all-rounder. Most neutral, excellent clarity, best in holographic imaging. May sound more like a smooth sounding solid state amp than an old classic tube amp. Not prone to microphonic.
 
Genalex GOLD LION E88CC:
Bold and beautiful. Also a very good all-rounder with better dynamic than JJ. Tight and powerful bass, bold and full bodied midrange, silky smooth treble. Tonality a tad darker than JJ. Very good detail and clarity, more or less similar to JJ. Not prone to microphonic.
 
Amperex PQ 6922:
Classic tube flavour. Musical with sweet vocal. Tonality slightly midrange centric. Relax presentation, and not very dynamic. Perceived detail and clarity are less than JJ and Genalex. Prone to microphonic.
 
 
 
 
This is the end of this rather long review
. I think I’ve covered pretty much everything from the sound quality and features of this wonderful little tube amplifier. It is now one of my favourite amplifiers for my daily use.
 
 

 
 
 
 

Specification from AT website:

 
MAXIMUM OUTPUT LEVEL    :
(10% at the time of 16Ω, THD) 500mW +500 mW 
(10% at the time of 32Ω, THD) 300mW +300 mW 
(10% at the time of 64Ω, THD) 150mW +150 mW 
(10% at the time of 150Ω, THD) 60mW +60 mW 
(10% at the time of 300Ω, THD) 30mW +30 mW
 
FREQUENCY RESPONSE        : 10Hz ~ 100kHz (-3dB)
TOTAL HARMONIC DISTORTION    : (32Ω, 20mW output) 0.25% or less
SIGNAL-TO-NOISE RATIO    : 100dB or more (JIS-A)
POWER REQUIREMENTS    : DC15V 1.2A (using the supplied AC adapter, Japan only)
INPUT JACKS            : Line input (Pink jack x2)
OUTPUT JACKS            : 6.3mm Stereo Jack
DIMENSIONS            : H79 × W105 × D142mm
WEIGHT (BODY ONLY)        : About 615g
ACCESSORIES            : AC adapter
 
 

 
 
 

Equipment Used In This Review:

 
 

 
Headphones:
Audio-Technica ATH-R70x
Audio-Technica MSR7LTD
Beyerdynamic T 1
Sennheiser HD 800
Shure SRH1540
 
Earphones / IEMs:
1964 Ears V3
DUNU DN-1000
DUNU DN-2000
DUNU DN-2000J
Puro Sound Labs IEM500
 
DACs, ADC, & Headphone Amplifiers:
HRT LineStreamer +
Light Harmonic Geek Pulse XFi
Mytek Stereo192-DSD DAC (firmware 1.8.1)
Violectric HPA V200
Yulong A28
 
Cables:
Atlas Equator MKIII Integra RCA cable (0.5m)
Better Cables RCA cable - Silver Serpent Anniversary Edition (6 inch)
Pangea Audio - USB cable - PCOCC & 4% silver - 2 Meters
Custom DIY cables
 
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 and foobar2000 v1.3.9
 
Measurement Instrument:
Amprobe Pocket Meter PM51A
Owon VDS3102 Digital Storage Oscilloscope
 
 
 
 

Some recordings used in this review:

 

 
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earfonia

Headphoneus Supremus
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This review would be incomplete without these pictures of heavily modded AT-HA22TUBE, belong to my friend @SiGiE.
I tried this ultramod HA22TUBE last June in a meet, and the sound is totally awesome! 

 
 

 

 

 
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earfonia

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lalala6

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I know I'm late to the party, but I tried the HA22TUBE at Canjam and was incredibly impressed at how it widens the soundstage and improves the timbre of many Audio Technica headphones, including the A1000Z, A2000Z, W1000Z and W5000. The imaging of this amp is uncannily holographic, something which I've never heard in any other amp. It also adds a very appealing flavor to the sound which is hard to describe. Hence I've ordered one for myself and it should be coming soon. Can't wait to hear how it sounds like with my AD1000PRM!

P.S. Nice review Earfonia! Your review is also part of what convinced me to get this amp. :)
 
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earfonia

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I know I'm late to the party, but I tried the HA22TUBE at Canjam and was incredibly impressed at how it widens the soundstage and improves the timbre of many Audio Technica headphones, including the A1000Z, A2000Z, W1000Z and W5000. The imaging of this amp is uncannily holographic, something which I've never heard in any other amp. It also adds a very appealing flavor to the sound which is hard to describe. Hence I've ordered one for myself and it should be coming soon. Can't wait to hear how it sounds like with my AD1000PRM!

P.S. Nice review Earfonia! Your review is also part of what convinced me to get this amp. :)

Never too late for getting good gears!
Welcome to the club and enjoy this wonderful little tube amp! :)
 
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HeavenNotes

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This is a Pro Review!!!  I´m enjoying more my amp today with IPad 3 as source, Audioquest Sydney cable 30 Pins to RCA and Grado RS1i  

 
 
 
 
 
 
I
 
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earfonia

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  This is a Pro Review!!!  I´m enjoying more my amp today with IPad 3 as source, Audioquest Sydney cable 30 Pins to RCA and Grado RS1i  

 
 
 
 
 
 
I
Nice! I saw you remove the tube grill.
 
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HeavenNotes

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  Nice! I saw you remove the tube grill.

Yes! I installed Amperex Orange Globe A frame tubes.  I love the sound and how it looks without grill. 
 
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ngominhhoang132

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Wow such a great review! I am seriously considering this amp for my MSR7. I just wonder does the RCA line output still work if I turn the HA22TUBE off? 
I want to use that output to connect to my speak amp. 
 
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ngominhhoang132

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Guys, I want to ship this amp to my country. Is the tubes well protected, what about risk of the tubes being broken during shipment? I am new to tubes :D
 
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HeavenNotes

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  Guys, I want to ship this amp to my country. Is the tubes well protected, what about risk of the tubes being broken during shipment? I am new to tubes :D
Hi. They are very well protected, but I really suggest you to upgrade to better tubes.  
 
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