Introduction
Drop has made some excellent collaborations during the past ten or so years and produced many, award winning, headphone amplifiers but all of them were solid state or tube hybrids. Thus Drop + xDuoo TA-84 is their first, all-tube headphone amplifier with an OTL topology.
Technical highlights
The amplifier is a collaboration between Drop and the Chinese manufacturer xDuoo who has a great expertise in the field of tube amplifiers. Drop + xDuoo TA-84 utilizes Output Transformerless (OTL) topology to manage signal without a transformer, greatly reducing distortion. For the preamp phase, it features dual ECC82 tubes and for the power amp phase, it runs dual EL84 pentodes.
The TA-84 utilizes xDuoo-designed capacitors in the power amp to do the job. They’re exceptionally quiet and impressively linear but since they’re outputting directly from the power tube, the output impedance of the amplifier is rather high, making it suitable for use with high impedance headphones from 100Ω and higher.
The Drop + xDuoo TA-84 is also equipped with a stepped potentiometer, which has 21 defined steps (each with a specific value of resistance) to help achieve unparalleled precision, reliability, and channel balance in output level. Paired with the gain switch at the back you can hit the perfect setting for your favorite pair of headphones or powered speakers. The difference between low and high gain is 16dB. The 21 steps are enough to allow every single step sufficient margin for fine adjusting the volume without loud jumps but the rotating action of the potentiometer is a little stiff and not smooth enough.
Furthermore the xDuoo TA-84 has an onboard USB DAC with one ES9018K2M DAC chip that supports input sampling rates up to 32bit/384kHz PCM and DSD256.
The xDuoo TA-84 has a preamplifier line output for both the line input and the onboard USB DAC. A very handy feature that allows you to experience tube sound with your favorite active monitors. Unfortunately the headphone and preamplifier outputs are simultaneously active and plugging a headphone will not mute the preamp.
Non Audio Stuff
The Drop + xDuoo TA-84 amplifier has an oblong, rectangular shape, measuring 26.8x16.3x11.6 cm, so it is quite tall but also narrow and compact enough to fit virtually anywhere as long as you have enough height clearance. The chassis has a full aluminum alloy construction with a smooth black finish and is exceptionally well made without sharp edges or corners.
The design is simple and minimalistic, this is a classic tube amplifier, the tubes are positioned at the front part and the power transformer is encapsulated in a box at the back. All four tubes are freely accessible and they are very easy to replace.
The front panel is plain and clean, the volume control knob is located at the center and underneath there is a status red LED and the 6.35mm headphone jack. Everything else is at the back; AC input plug, power on/off switch, voltage selector switch, USB type-C input, RCA line input, RCA preamp output as long as gain and input selector switches.
The amplifier has a soft start feature that allows about two minutes of tube warm time before it switches on. Operation is pretty simple, you can either use the line input with your favorite source or the onboard USB DAC without the need to install drivers.
Power output
The rated output power is 44mW/100Ω, 83mW/300Ω and 93mW/600Ω. These numbers might look low and underwhelming but don't pay attention. This is an OTL amplifier that produces the great voltage swing that is needed for driving high impedance headphones. The xDuoo TA-84 is very powerful when it comes to such loads and can drive all high impedance headphones without breaking a sweat.
I have tested the amplifier with the Sennheiser HD8XX (300Ω), Sennheiser HD660S2 (300Ω), Sennheiser HD650 (300Ω) and the iBasso SR3 (150Ω). The amplifier literally blew them away, it drove all of them with excellent dynamics and surplus of headroom at just ¼ of the volume range at the high gain setting.
The amplifier has a low noise floor, it is not dead silent but you have to raise the volume above middle to start listening to some tube hiss and transformer noise. There is no point in discussing the behavior with low impedance, high sensitivity headphones since the xDuoo TA-84 is not made for them.
Stock tubes
The stock ECC82 and EL84 tubes that are included in the package are from the Psvane classic series but they seem to be OEM made for bulk production without thorough quality inspection and any kind of matching.
Both the ECC82 tubes that came with the review sample were very microphonic and one of them was also defective as it produced heavy background hissing noise. The power tubes were good but in the end I have decided to replace all four of them.
Both types of tubes are quite common, they are currently produced by all known manufacturers and they are not too expensive. After checking prices and availability, I decided to order matched pairs of JJ Electronic tubes for both the ECC82 and EL84 variants.
After replacing the tubes, the amplifier became silent without producing background hiss or microphonic noise and worked just fine. Furthermore, the JJ EL84 power tubes proved to be more dynamic, controlled and technically potent than the stock ones so I suggest that you should do some tube rolling to get the most out of the amplifier.
Audio stuff
The sonic performance of the xDuoo TA-84 is really great, this is an amazing little amplifier with a favorable and immensely enjoyable sound character that combines plenty of tube magic with very competitive technicalities that are easily comparable with solid state amplifiers of the same category.
The sound is slightly warm, rich and harmonious with great musicality and an incredibly analog character. The timbre is natural, organic and realistic, all acoustic instruments and voices are reproduced with an extremely lifelike manner, the most colorful harmonies and varied overtones.
The xDuoo TA-84 amplifier has a modern way of thinking when it comes to its tube implementation. The audio circuit is designed as neutral as possible without adding much coloration to the sound or altering the linearity of the measured frequency response. This is not like some old tube amplifiers that used to mess with frequency response, mute the treble or boost the mids and the bass to make the music sound syrupy, warm, blurry, hazy and slow without much control and definition.
Technicalities are kept solid and very competitive, the xDuoo TA-84 is a neutral and linear sounding amplifier without compromising in treble extension and clarity. The sound is sparkling and energetic with great definition and excellent detail retrieval for such a type of an amplifier. The bass is fast, tight and controlled with good layering and the mid-range is spacious, present and well defined without any significant coloration.
So, someone would ask what's all the fuss about tubes? Well, what really happens is that the tubes have the ability to mostly enhance even harmonics throughout the whole frequency range, making for a pleasing and smooth sound with analog-like characteristics and plenty of musicality. They add extra weight to the low-end which is visceral and full bodied while maintaining great dynamics and physical impact. Full bodied and weighty are also the mid and higher frequencies so the sound is very cohesive without exhibiting any kind of weight loss in the treble. The decay is natural, the notes fade away in a timely manner, not too fast or too slow and are finely sculptured with a holographic relief.
There are solid state amplifiers of the same price category that are definitely more technical sounding, with better transparency and clarity, deeper detail retrieval and more impactful bass but none of them can match the inherent musicality, the harmonious nature and the music fluidity of the xDuoo TA-84.
No competitive solid state amplifier is as visceral and full sounding as the Drop + xDuoo TA-84 and only few of them can match the holographic properties of its soundstage. The soundstage is amazingly open and spacious, both expanded and deep with largish images. You can certainly find several solid state amplifiers that can surpass the xDuoo TA-84 in imaging precision and positioning accuracy but no one of them can sound more holographic and majestic.
The DAC
The onboard DAC is crystal clear, linear and transparent so it pairs well with the plethoric nature of the amplifier. Very good and satisfying performance to boot up or when funds are limited but honestly, the xDuoo TA-84 scales incredibly well and you are going to do much better with a high quality, external source.
Conclusion
The xDuoo TA-84 might be Drop’s first all-tube, OTL headphone amplifier but I think that is their best sounding product thus far. Musical, engaging and analog sounding, this is a great amplifier with competitive technicalities, great tube rolling potential and plenty of power to drive all high Z headphones. Well made and sturdy, with a high quality onboard DAC and preamplifier output, the Drop + xDuoo TA-84 represents an excellent value and is one of the best OTL amplifiers you can buy without the need to break the bank. Actually, given the current offerings in the market, you will have to spend at least double the money in order to get something marginally better than the xDuoo TA-84 so I would suggest you hurry and get one while it is still available.
The review sample was kindly provided free of charge.
The price of the amplifier is $399 and is exclusive available from Drop.
As far as I understand there is no balanced output so I need to change cables all the times. Or to use an adapter balanced to unbalanced plus 6.35 adapter on top.