Products like the Drop+Xduoo TA-84 OTL Headphone Amplifier have headphone enthusiasts such as myself extremely excited in 2023; and not just because of the affordable price tag. $349 USD for this amplifier is a steal.
One of the best aspects of the Head-Fi revolution has been the growth of high-end Chinese brands in the market; Topping, Questyle, and Xduoo have all successfully carved out niches for themselves in the desktop headphone category and all of them offer highly competitive products at prices that a lot of consumers can afford.
The TA-84 is a collaboration between the two brands and there is no question that Drop was instrumental in bringing the Sennheiser HD650 to a much larger audience with their HD6xx headphone.
The success of the collaboration surprised both Drop and Sennheiser and forced them to make the HD6xx a permanent product rather than just a group buy opportunity.
We would not be taking a huge leap suggesting that the Drop HD6xx, HD600, HD650, and Drop HD58x are the most popular audiophile headphones sold over the past decade.
Because of that level of success, Drop decided that it needed to offer a new headphone amplifier for its existing headphones lineup.
There have been a number of successful tube headphone amplifiers over the past decade and a number from Xduoo that I have recommended as good entry points into the category. They have successfully figured out how to make reliable models and when Drop was was looking for a partner to help build a tube amp designed for the HD6xx headphone, Xduoo was high on their list.
What I find more exciting is that Drop and Xduoo went with a new topology rather than rebadging an existing Xduoo amplifier.
Drop wanted an output transformer-less (OTL) amplifier, because those generally offer the best performance using high impedance dynamic driver headphones like the Drop/Sennheiser HD6xx and HD8xx.
There is a trade-off associated with this because designs without an output transformer offer better linearity and lower noise, but are not suitable for low impedance headphones.
Potential buyers should be aware of that reality when listening.
Xduoo already had the TA-26 OTL amplifier in their lineup and could have gone with that, but finding solid and reliable 6SN7 driver tubes is much harder when operating on a budget.
Musicians love to hoard all of the 6SN7s for their amplifiers and most of the really inexpensive variants are not very good tubes.
If you are willing to spend as much on the tubes as the amplifier itself, the TA-26 can be turned into a great sounding amplifier — but most budget listeners are not looking to spend that kind of money on tubes.
The new TA-84 utilises the EL84 which is a single pentode design originally designed for radio applications but became very popular in guitar amplifiers in the 1950s and 1960s.
The EL84 is capable of roughly 2 watts of output from a single tube making it a great option for driving headphones. Finding quality EL84s (new or NOS) is much easier even with tube prices slightly bonkers right now.
TA-84
The new TA-84 DAC/Headphone Amplifier is an OTL (Output Transformerless) design that utilizes EL84 power tubes and 12AU7 driver tubes. Xduoo’s TA-26 OTL Headphone Amplifier which was clearly the inspiration for the new amplifier does not include a DAC and also utilizes a single 6SN7 driver tube and 6AS7 output tube instead. The TA-84 uses a single EL84 tube per channel.
For a deskstop DAC/Headphone Amplifier, the TA-84 is on the larger side measuring almost 12″ W x 5″ D x 6″ H and weighing 6.6 pounds. The anodised aluminum case gives the unit a rather hefty feel in your hands.
The stock unit comes with PSVANE-branded tubes and provides 93mW of power into 600 ohms with a voltage swing of roughly 6 Volts.
The industrial design is fairly conventional with the TA-84 and that should be considered a positive development; the front panel features a single 6.35mm headphone output which is located beneath the volume control that features a 21 step potentiometer. When you combine that with the gain settings, you have 42 distinct volume steps.
In actual use, I discovered some overlap between low and high gain which means that there are 33 distinct volume steps.
The tube sockets are accessible from the top with drivers in the front row and power tubes behind them, followed by the input transformer.
The rear panel serves as the gateway to the other side of the package; the ES9018K2M 32-bit/384kHz PCM DAC. Those with the need for DSD or MQA support will have to use another external option and use one of the analog inputs as a point of entry.
The panel also offers two switches; one for gain (High and Low) and the second for the input source (USB or AUX). There are two sets of inputs (USB and RCA), a fused power outlet, 110/220 switch, and a power switch complete the panel.
Listening
The TA-84 was designed to offer a unique amplifier/DAC option for the HD6xx and it only made sense to start there with our testing.
The amplifier was connected to my laptop using the USB connection and I fired up Foobar to run the pairing through my test tracks.
The initial takeaway was that the HD6xx requires the TA-84 to be used on the high gain setting to achieve normal listening levels with adequate headroom above that.
Using the amplifier on the low gain setting, I did not reach normal listening levels until almost stop 17 out of 21 on the volume knob; the high gain achieved the same listening levels on stop 9 giving the HD6xx a lot more headroom to deal with large dynamic hits. There was also some audible distortion if I listened too loudly on the high gain setting.
The combination acquitted itself rather well; the low end featured some additional warmth which extended into the lower midrange and there was an organic feel to most of this range.
The HD6xx doesn’t offer a lot of sub bass information and impacts were still slightly softer in the range below 100Hz.
Above that, there was some additional impact and depth with kick drum coming across as more natural sounding than timpani.
The additional coloration in the lower midrange fleshed out male vocals rather well, but at the expense of some clarity and detail.
The midrange overall became too organic sounding, which prompted me to switch out the HD6xx for the HD8xx which offers greater clarity, detail, and a higher level of resolution.
The treble extension using the HD6xx was rather good and only hindered by the drivers inside the headphone and not the amplifier. Percussion snap was solid and not quite as sharp as some other headphones; cymbals had more than enough energy to sound realistic.
Switching to the HD8xx, there is some additional low end impact and definition, along with some extra top end energy and detail.
The overall tonal balance helps to tame the additional treble hardness making the TA-84/HD8xx a more relaxed sounding combination.
When I switched over to my RME ADI-2 FS B, the clarity and detail improved substantially but that came at the expense of overall texture and the top end became far too aggressive.
Vintage Headphones?
If you are new to the headphone space, it is unlikely that you would have any experience with the 50 year-old AKG 240 Sextett. The Sextett was a rather unique headphone and the first of the AKG 240 models introduced that featured 6 passive radiators surrounding the main drivers.
The impedance (600 Ohms) is actually slightly higher than the quoted specification and I know that because of how some Dongle DACs respond to it. More than a few switched over into “line-out” mode when connected.
Later iterations of the 240 dropped the passive radiators because they were too expensive to manufacture and match and instead used foam to allow sound from the rear of the driver to reach the listener’s ear.
My 50 year-old pair still work, but the original vinyl ear pads deteriorated and have since been replaced with a set of Dekoni sheepskin ear pads that alter the sonic signature; the low end has greater presence compared to with the original ear pads supplied by AKG.
Because of the high impedance, the AKG 240 demanded a bit more twist of the volume knob than either the HD6xx or HD8xx. The sub bass performance was similar to the HD6xx in terms of quantity, but it was better defined and cleaner sounding overall.
The mid bass was also superior with very strong impact, excellent articulation, and rather detailed. Percussion was most certainly felt and it was fascinating that a vintage pair of headphones could outmuscle a relatively new pair with more advanced drivers.
The 240 also offers a cleaner transition from the mid bass into the lower midrange compared to the HD6xx.
Both male and female vocals cut through the mix well and were placed only slightly in front of the instrumentation. Guitars are delivered with an angry growl and strong edge making the 240 a much better pairing for rock and alternative music with the TA-84.
The upper midrange and lower treble have a mild lift, which flattens out before shifting upwards around 10kHz giving the top end some additional airiness and detail.
Some might find the additional energy in the treble range to be somewhat fatiguing but the TA-84 did a really nice job taming it. Considering their age, the AKG 240 Sextett are a rather engaging listen.
Before you run out looking for a pair — a word of caution.
AKG released a 240 Studio model some years back with a very different impedance (55 Ohms) and it is not suitable for use with the TA-84. If you do own one of these headphones, make sure it is the high impedance model before plugging them in.
I’ve started doing some tube rolling with the TA-84 and will publish a full tube-analysis on audiofool.reviews once complete; it’s accurate to say that the differences with most of the aftermarket tubes and the tubes that ship with the TA-84 are smaller than with previous Xduoo amplifiers.
The PSVane tubes are a good middle of the road option and while a Mullard ECC82 will make the sound a bit warmer and more fluid, and a Siemens 12AU7 can dry it out a bit and make the sound a bit leaner and cleaner — this should be considered a method of tone control and not a major upgrade of the overall sound quality.
Final Thoughts
The Drop+Xduoo TA-84 OTL Headphone Amplifier is an excellent value at $349 when you factor in the overall sound quality, supplied tubes, and rather capable ESS DAC. It certainly offers a really well made affordable option for those looking to get the most out of their high impedance, dynamic driver headphones.
OTL amplifiers, however, are not for everyone for the simple reason that they do not play well in the sandbox with planar magnetic, balanced armature, or low impedance dynamic drivers.
That does limit your options somewhat, but one can find high impedance studio models from AKG, Beyerdynamic, and Sennheiser and other manufacturers.
These types of headphones have been available for 50 years and some can be found used at some bargain prices.
The TA-84 impressed me so much with the AKG 240 Sextett that I may have to add it to my collection. Quirky for sure. But you should hear how these 50 year-old headphones perform with this little black box. You might be as impressed as I was.
Where to buy: $349 at drop.com (expected to ship by December 22, 2023)
Related Reading
