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    Review | Abyss AB-1266 Phi TC Headphones and HeadAmp GSX mk2 Balanced Headphone Amplifier

    Many consider the Abyss AB-1266 Phi TC headphones to be the best in the world. These US made 'phones certainly vie for the title of best planar dynamic 'phones, if not the best in terms of absolute sound quality. Built like an Abrahms tank, and somewhat unusual looking, these New York State built 'phones certainly do impress in terms of their build quality. At first glance, they look a lot like a medieval torture device, perhaps a chastity belt for one’s ears, but aside from being somewhat heavy, these 'phones are really not uncomfortable at all, but more on that later. 


    The HeadAmp GSX mk2 headphone amp is a balanced design made for magnetic 'phones only. Made in Charlottesville Virginia, USA, and consisting of two slim (single rack height) chassis, the GSX mk2 is at least as well made as the Abyss ‘'phones which means that they are as well made as it is possible to do in a production unit, and I guarantee, nobody builds quality better than HeadAmp. We Americans do not make as much electronic stuff as we used to, but it seems that when we do, we knock it out of the park. This amp is gorgeous in the review sample’s red anodized livery but is also available in an impressive array of other colors, such as black, brushed aluminum, two shades of blue, green (!), white, gold, charcoal gray, and purple (lavender?). Whew!









    HeadAmp GSX mk2


    Usually at this point in a review of a piece of electronics hardware, I give the dimensions. Unfortunately, in this case I couldn’t really do that by measuring them because the units have been returned to their owner and I was counting on the website to give me those measurements. They aren’t anywhere on the site that I could find, and indeed, they aren’t even in the 4-page user “manual.” I have already said that the units are both a single rack component in height. So, a call to Justin Wilson, the proprietor of HeadAmp gave me the rest of the dimensions. Each of the two units (power supply and main amplifier chassis) is 14.5 inches (368.3 mm) wide by 9 inches (228.6 mm) deep by 2 inches (50.8 mm) high. The price of the HeadAmp GSX mk2 is US$2995. The optional blue or red color is an additional US$200 (don’t know if the others, apart from black and brushed aluminum colors demand a premium or not).



    Panel Layout of the GSX mk2


    The front panel of the amplifier section for the GSX mk2 contains outputs for magnetic headphones as well as the controls for the amp. Starting from left to right there is the on/off switch which either enables or disables the rear panel pre amplifier outputs. Although HeadAmp calls it a power switch, it’s more of a standby/operate switch as the real “power switch” is located on the front of the power supply chassis. Next we have the gain select three position miniature toggle switch. This allows the user to choose the overall gain of the amplifier for Low gain (0.9dB), Medium gain (12.5dB), and High gain (21.2dB). Next, there is an “operate” LED to indicate that the unit is on and not in standby mode. Then there’s a 4-pin female XLR for balanced headphones that use a single XLR plug for both right and left channels. The wiring for this connector is L+ (pin 1), L- (pin 2) R+ (pin3) and R-(pin 4). To the right of the 4-pin XLR are a pair of three pin XLRs of the combination XLR/1/4 inch, TRS 'phone jack type for balanced outputs that use either three-pin XLRs or “stereo” 'phone plugs. Next there is the true DACT stepped attenuator for the volume control. This used to be a US$200 option, but in 2017, HeadAmp made the stepped control standard on all units. Finally, there is an input toggle switch. It chooses the rear panel input as either the  RCA-1 input jacks, the XLR inputs, or the RCA-2 inputs. For true balanced headphone operation the XLR inputs on the rear must be used. 


    The back panel of the GSX mk2 amp contains all of the I/O. Again, from left to right, a pair of 3-pin XLRs for balanced input, two pairs of RCA jacks (RCA-1 and RCA-2) for unbalanced input and next there is a pair of XLR male outputs and two RCAs called loop outputs. This allows the user to pass the input signal on to another part of your system. When set to standby mode, only the RCA pair are energized. Next in line, to the right is the audio output connections, these consist of another pair of 3-pin male XLRs and another pair of RCA jacks. Finally, there is a six-pin circular male jack for the umbilical that connects the amplifier chassis to the power supply chassis. 


    The second chassis, the power supply, is an identically sized chassis with a power toggle switch on the front left and a female umbilical connector for the power supply cable in the center of the rear chassis. Finally, there’s an IEC connector for the AC mains cord. 




    Abyss AB-1266 Phi TC closeup.jpg



    Abyss AB-1266 Phi TC Headphones


    Starting at $4,995.00, the Abyss AB-1266 Phi TC model headphones are a very premium product. As such they need to be coupled to a really high-class state-of-the-art headphone amplifier. This is the reason why these 'phones are being paired with the GSX mk2 for this review. 


    These 'phones have a build quality that’s practically unheard of, in even the rarified environment of mil-spec or aerospace, much less in a consumer product. Abyss says that they make everything in-house even the screws used to manufacture these 'phones! This attention to detail is apparent even as you take the 'phones out of their packaging. The ear-cups are CNC machined from a solid billet of aluminum and the ear-pads are a thick, padded, very soft lambskin which provide an acoustically tuned space between the diaphragm and the listener’s ear for maximum sound quality. The diaphragm on the 'phones is of an exceptionally low mass and is powered by custom and very powerful neodymium magnets. The back wave of each perfectly matched pair of drivers is a proprietary foam, which even though it looks like spun plastic, is actually made of spun aluminum and designed to control resonance and help linearize the diaphragm movement. 

    The earpieces on these 'phones do not pivot. But the head frame is separated in the middle and slotted. This allows for the movement of the ear-cups either closer or further away from the listener’s head to effect a perfect fit. A single finger-screw holds the two halves of the head frame together and not only allows one to adjust the width of the two ear-cups, but also allows for the two halves of the head frame to pivot with respect to one another, allowing the listener to adjust the parallel orientation of the ear cups to fit the wearer’s head. This head frame does not touch the wearer’s head however, for below it is stretched a padded leather headband which rests on the wearer’s head. It should be noted here that these 'phones are not designed to clamp the listener’s head in the vice-like grip that many headphones need to  afford a good bass seal. They are meant to “float” against the ears, with their weight perfectly balanced and resting atop the listener’s head. While, admittedly, they look awkward (if they seem heavy, it’s because they are at just a hair under 23 ounces [646 grams]), but they are actually much more comfortably than they look and can be worn for hours without causing fatigue. The AB-1266 Phi TC 'phones have a 42Ω impedance, with a ± 0.1Ω tolerance, so they should cause no problems with any headphone amp with which they are paired. The capsule matching, right to left, is 11.1dB which is exemplary. 


    The Abyss AB-1266 are available in several different configurations. While the actual ‘'phones themselves are the same in each, they come with differing accessories. 


    The “Lite” model is US$4,995.00 and comes with a balanced 8 ft  (2.5 meter)  4-pin XLR connector and a flexible ¼ inch adaptor (all cables are built by JPS labs specifically for Abyss). This configuration comes with a velvet carrying bag (although all models come packaged in a hand made, velvet lined presentation box). 


    Abyss AB-1266 Phi TC whiskys.jpgThe “Deluxe” edition, at US$5,995.00 comes with two cables: a dual balanced, 8 Ft (2.5 meter) 3 pin XLR cable set (this means two distinct cables; one for each ear-cup. They do not combine into a “Y” as do most headphone cables. This model also comes with a “Y” adaptor to convert the cables to a standard 1/4” 'phone plug; The Deluxe also comes with a handcrafted leather “man purse”  with room and pockets for an iPad, a music player, and an amp (such as the iFi xCan) allowing for a complete portable music system (these 'phones are not real efficient at 98.4 dB/1volt @ 1 KHz, so I don’t fully endorse using these 'phones in a portable setup; not least because they don’t provide or seem to offer a 3.5 mm (1/8”) adaptor or plug to use with portable audio equipment). Finally, the Deluxe set comes with a heavy aluminum extended-height headphone stand, laser engraved with the ABYSS logo. 


    Finally, the “Complete” model (US$7,995) comes with an upgraded JPS Labs “Superconductor HP” balanced 8 FT (2.5 meter) cable, with a choice of dual 3 pin or 4 pin XLR cable sets, and a 1/4" (6.3 mm) adaptor (plus a 4 pin XLR Y-adaptor with dual 3 pin connectors). (Custom cable lengths are available at extra cost). Also included in the “Complete” ensemble is the same leather handbag that comes with the “Deluxe” configuration along with the same headphone stand.



     The Abyss AT-1260 Phi TC 'phones AND the HeadAmp GSX mk2 Amplifier Together. The Sound of Perfection!


    I received these 'phones and the HeadAmp GSX mk2 while I was reviewing the Stax SRM-700T amp and the Stax SR-009S electrostatic headphones, so I had a true state-of-the-art reference with which to compare them. Not only are the two systems the crème de la crème of headphone systems, they are comparable cost-wise as well. The Stax combo came to US$8,350.00 and the Abyss/Headamp system (using the base configuration of the Abyss 'phones for comparison) came to US$7,950.00. A difference of a mere $360.00. 

    If you read my review of the Stax duo, then you know that I regard it as the “holy grail” of headphone listening, something to which all of us audio Sir Galahads should aspire. And I stand by that conclusion, but I must say that the combo of the HeadAmp and the Abyss is right up there with the Stax setup! 

    There are differences in presentation, of course, but they are fairly minor. While the SR-009s have better, deeper bass, the Abyss have more “slam”. Explosive transients and bursts of acoustic energy are much more palpable with this review duo than with the Stax, but the Stax seems to exhibit slightly more high frequency air and delicacy than do the Abyss/HeadAmp. That’s not to say that the latter are in anyway deficient in this regard, but where the Stax top end is “feathery” in it’s presentation, the Abyss pairing is more solidly grounded, that is to say, that the latter have a top that’s a tad “harder”.


    As far as distortion is concerned,  I would expect that the Stax pairing would be audibly cleaner. But, when listening at very well matched volume levels (less than a dB) the difference in distortion between the two is pretty much too close to call! I didn’t expect that!  Which is sonically the best? Like anything else in audio it comes down to personal taste and in this case, more than many others


    The final answer for me was the Stax setup. The reason comes down, partially to ergonomics, but sonic character also plays a large part in my decision. I prefer the light and airy high frequency response of the Stax setup coupled with that extra soupçon of bass response to the more explosive dynamic slam of the Abyss/HeadAmp duo. In the midrange, both 'phone systems excel in their portrayal of vocals and brass.  Again the Abyss are a bit more forward in the midrange and give a “close-up and personal presentation” with the upper midrange, especially on vocals, and on the high frequency overtones, but there is much to be said for both presentations. My friend who owns the Abyss 1266 Phi TC and the HeadAmp GSX mk2 likes them better than he does the Stax. I suspect his reasoning stems from the fact that the music to which we each listen is a bit different. While he enjoys classical and jazz, he listens to a lot of rock. So the dynamic slam of the Abyss setup suits him better than the subtleties of dynamic contrasts and micro dynamics to which the Stax ‘phones and amp are capable.


    I can understand that, for when comparing the two headphone systems on the Jefferson Airplane album Surrealistic Pillow The driving beat behind “White Rabbit” or “Somebody to love” has a lot more impact through the Abyss/HeadAmp than through the Stax. But the difference between the “slam” of the two 'phone systems is largely lost on, for instance, Dave Brubeck’s landmark album, Take Five. The exception is the drum solo in the “Take Five” cut. On that, the percussive drive of the drums definitely favors the Abyss setup. On that cut, the Stax pairing is much more “polite”.  On classical music such as Bartok’s “Miraculous Mandarin” with Eugene Ormandy and the Philadelphia Orchestra or the recent John Williams/Anne-Sophie Mutter album Across The Stars on Deutsche Grammophon, the first cut, “Rey’s Theme” from one of the Star Wars films, the bass line is much more fulsome on the Stax SR-009S/SRM-700T than on the Abyss/HeadAmp. The owner of the Abyss/HeadAmp combo’s previous headphone “love” was a pair of Sennheiser HD800s which also have the characteristic of explosive dynamics or “slam”. I can see where this “slam” is really impressive (and probably addictive) on rock and other percussive music. 


    Ergonomically, I also find the Stax SR-009S more appealing. While the Abyss look almost military and inelegant, the Stax seem to be more refined. Once adjusted for my head, the Abyss fit well, and aren’t uncomfortable but they are fiddly. The Stax, by comparison are light and once the head strap is adjusted, one only has to pick them up and put them on. I also find the Abyss with it’s two separate and fairly stiff cables; one for the left ear-cup and one for the right, to be quite awkward.





    Basically, Both of these systems represent state-of-the-art of headphone design (I haven’t heard the RAAL-Requisite SR1a Earfield Monitors, but from Chris’s review, they might be in a position to knock one or both of these 'phones off of their pedestal). Both sound unbelievably good and present the ying and yang of a “neutral” presentation. Anyone who takes their headphone listening seriously would be hard pressed to find major fault with either of these headphone ensembles. The choice, in the end, will be a matter of subtle differences in presentation coupled with aesthetic and ergonomic considerations. If you are in the market, I recommend that you give both of these fine systems serious consideration. 






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    Community Star Ratings and Reviews


    I encourage those who have experience with the AB-1266 Phi TC or GSX mk2 to leave a star rating and quick review on our new Polestar platform.








    User Feedback

    Recommended Comments

    Really enjoyed the headphone review. TOTL headphones have been under appreciated in content on AS but its really pushing understanding and knowledge ....just pleasurable. Keep them coming.There are a few more id love to see on my wish list in a well written review.

    Head Amp have a strong pedigree, thier headamp gilmore mk2 was an afforable choice that still gives me musical enjoyment. Crystal clear and uncoloured. 1/3 cheaper now..

    My Dan Clarks Ether2 works very well with it.  I dont know if i could take Torquemada's personal headphones after the Ethers feather light engineering, but id love to hear that slam on EDM.

    Quoting Hannibal Lecter "we covert what we see" "What we read" works just as well. 


    I think a small interview the reviewer on his piece would work at the end of an article. If Chris and the would be reviewer choose too

    .A few questions and final thoughts in a little podcast. You can read the enthusiasm but a short conversation may add an extra dynamic. 


    Thanks @Sonis  good job..


    Kind regards






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    Hi Sonis,


    Thanks so much for writing this review and your companion piece on the Stax.  I decided a few weeks ago that COVID-19 meant that I had to resume my on and off quest for a price-no-object pair of headphones.  Sadly, of all the flagships, only the Focal Utopias are available at New England dealers, so reviews are absolutely essential.  Your reviews were the most helpful anywhere because you compare the character of stellar products in a completely even and thorough way--even down to the "better" bass of the Stax compared to the better "slam" of the Abyss.   I have the Stax on the way.  Thanks!



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