Drop + THX AAA One Linear Amplifier Review - New reference headphone amplifier at $200

Drop + THX AAA One Linear Amplifier Review - New reference headphone amplifier at $200

Review written by @Resolve

Review unit provided for evaluation by Drop.


The $200 Drop + THX AAA One comes hot on the heels of the very popular THX 789, that many listeners have enjoyed over the past several years as a reference style balanced amplifier. In fact, the 789 was so popular that used prices started to get dramatically inflated, simply due to lack of supply and increased demand. Drop has since done additional runs and even reduced the price to keep up with the competition for this style of amplifier, now coming it at a mere $299.

But, there are still a number of listeners who have no use for the massive 6W the 789 has on tap, nor do they have need for its balanced output. For the majority of headphones, this is an absurd amount of power output. Couple this with headphones getting more and more efficient these days, and for many there really hasn’t been much reason to look into any of the THX AAA amps… until now.

Drop + THX AAA One Linear Amplifier Review | Headphones.com

What It Is

The Drop X THX AAA One is a $200 single ended linear headphone amplifier. This is essentially the little brother of the well known, more expensive THX 789, which is a balanced amplifier. In general, this is a good thing, since it uses the same AAA topology, which promises ultra low intermodulation and crossover distortion. Specs aside, the THX AAA One has three gain stages, -12, 0 and +12, making it extremely versatile for both full-sized headphones that take some power (2.7W @ 32 Ohms), and highly sensitive IEMs like the Campfire Andromeda. Moreover, the THX AAA One has a low output impedance of less than 0.1 ohms, meaning that for the Andromeda, or other output impedance dependent headphones and IEMs, the THX AAA One won’t change the frequency response. Lastly, the One also has preamp functionality on the back that can be used for speakers or other parts of a system.



  • All parameters measured at 0 dB gain, 1 kHz, with unbalanced inputs and 300-ohm load unless otherwise noted
  • Inputs: Stereo RCA gold-plated
  • Outputs: 1/4 in (6.35 mm), TRS gold-plated Neutrik, Stereo RCA preamp gold-plated
  • Frequency response: + 0.01 dB / - 0.03 dB 20 Hz – 20 kHz
  • Input impedance: 1 kOhms
  • Crosstalk: -93 dB, 300 ohms: 0.002240%
  • Noise (A-wt): 0.95 uV, potentiometer at nil
  • SNR: 140.2 dB, 300 ohms, <10% THD
  • Gain: 0.25x , 1.0x, 4.0x (-12, 0, +12 dB), selectable via front switch
  • Chassis: High-grade CNC-milled aluminum with bead-blasted finish
  • Power supply: 30 VDC inline brick, universal input 100 – 240 VAC
  • Dimensions: 8.1 x 8.1 x 1.5 in (20.7 x 20.6 x 3.9 cm)
  • Weight: 2.6 lbs (1.3 kg)

Single-Ended Output

  • Output power: 1500 mW, 16 ohms, <1% THD (watts per channel)
  • Output power: 2700 mW, 32 ohms, <1% THD (watts per channel)
  • Output power: 280 mW, 300 ohms, <1% THD (watts per channel)
  • Output power: 140 mW, 600 ohms, <1% THD (watts per channel)
  • THD: -142 dB, 300 ohms, 1 mW: 0.000008%
  • THD: -118 dB, 300 ohms, 100 mW: 0.000126%
  • THD: -120 dB, 32 ohms, 1 mW: 0.000100%
  • THD: -130 dB, 32 ohms, 100 mW: 0.000032%
  • THD: -117 dB, 16 ohms, 1 mW: 0.000140%
  • THD: -132 dB, 16 ohms, 100 mW: 0.000025%
  • IMD: -114 dB, SMPTE 70 Hz + 7 kHz, 300 ohms, 1 V: 0.000398%
  • IMD: -131 dB, DFD 18 kHz + 19 kHz, 300 ohms, 1V: 0.000028%
  • Crosstalk: -93 dB, 300 ohms: 0.002240%
  • Noise (A-wt): 0.95 uV, potentiometer at nil
  • SNR: 140.2 dB, 300 ohms, <10% THD
  • Gain: 0.25x , 1.0x, 4.0x (-12, 0, +12 dB), selectable via front switch
  • Output impedance: < 0.1 ohms

Preamp Output

  • Output voltage: 9.0 V / +21 dBu, <1% THD, 600 ohms load
  • Output power: 140 mW, 600 ohms, <1% THD (watts per channel)
  • Output impedance: < 0.1 ohms
  • THD: -142 dB, 600 ohms, 1 mW: 0.000008%
  • THD: -118 dB, 600 ohms, 50 mW: 0.000126%
  • IMD: -114 dB, SMPTE 70 Hz + 7 kHz, 600 ohms, 1 V: 0.000398%
  • IMD: -131 dB, DFD 18 kHz + 19 kHz, 600 ohms, 1V: 0.000028%
  • Crosstalk: -110 dB, 600 ohms: 0.000300%
  • Noise (A-wt): 0.95 uV, potentiometer at nil
  • SNR: 140.2 dB, 600 ohms, <10% THD
  • Gain: 0.25x , 1.0x, 4.0x (-12, 0, +12 dB), selectable via front switch

Drop + THX AAA One Linear Amplifier Review | Headphones.com

How It Sounds

Headphones Used:

At this point I have to stress that most good budget amps either sound the same or very similar to one another, so all differences I’m about to express here are extremely minimal.

As the name suggests, the THX AAA One Linear Amplifier has a linear, reference style sound - one that’s reminiscent of its bigger brother the THX 789. It’s extremely clean sounding with a totally dead background, regardless of the headphones being used. One point of difference between the One and other lower end amps is that while they can often get loud enough, they don’t do anywhere near as well for the sense of space, image separation and distribution, with more of a focus on center image. 

Comparing the One with certain budget DAC/Amp combos meant more for portable use like the Khadas Tone2 Pro (also around $200) was a night and day difference for overall sense of lateral definition, with the One handily beating the Tone2 Pro. Of course, this is maybe an unfair comparison given that the One has a much larger footprint and isn’t meant for portable use - but it still does reveal the benefits of a full sized desktop amplifier like the One over these other smaller devices.

So, the One’s focus is on accurate soundstage and space, while remaining analytic and articulate - again, other amps do this as well, but not all. Comparing it directly with the Schiit Audio Magni 3 Heresy and the Topping L30, the One again seemed to do a better job of filling in the lateral space for front left and front right. I feel as though it’s not actually enhancing the soundstage, but rather giving sounds that fall left and right of center better definition and presence, contributing to an enhanced sense of ‘fullness’.

Additionally, I find the One to be more analytic than what I’m used to at this price - nothing gets smoothed over and you get all the information. Once again, this sounds like a reference class amplifier, and in my mind that’s a very good thing.

Now, with all of that said, there are some listeners for whom this description may not be ideal. There’s a worry that this style of amplifier can be a bit too ‘sterile’. To that I have to say that yes, there is a kind of blandness to the One in the sense that it doesn’t add anything or conserve second and third harmonics to change the sound. But, it’s also not dead and lifeless, like I would describe the Topping A90. In fact, this may be a bit controversial, but I was comparing the One back and forth with the A90 and found that I preferred the One. 

The A90 measures well, but it has the effect of sucking the joy out of every headphone I try to run off of it, and I don’t have that issue with the One, which also aims for a reference style sound. I suppose there are two ways to approach this - one is to see who wins at the measurement wars, and the other is to see which one sounds better, and to me the One beats the A90 for the latter evaluation. Moreover, the One doesn’t have any ground loop issues when being run from a USB DAC, so that’s another win there. But, I digress, and will review the A90 in another article.

Drop + THX AAA One Linear Amplifier Review | Headphones.com

Who It’s For

As mentioned, the THX AAA One is extremely versatile, as it can power medium hard to drive headphones, and highly sensitive IEMs without noise floor issues whatsoever. For that reason, the One is for those who have varying power requirements for different headphones - or those who own both over-ear headphones and IEMs, and want the convenience of not having to use different devices for both applications. 

Moreover, the One is also for those who frequently forget to turn off their equipment when done using it. I say this because the One doesn’t get warm, making it ideal for using in a stack. There’s also an additional feature/quirk with the One that it seems to power down or go into sleep mode without having to toggle the power switch. When you start to play music again, there’s a small click and then it powers itself on again after half a second. 

Lastly, the One is for anyone looking for that transparent, analytic presentation that gives you all the information, similar to what you get with the THX 789.

Who It’s Not For

On that subject, the THX AAA One is not the amp to get if you intend to run extremely power hungry headphones. It’s at this point that I have to stress that 2.7W is actually a lot of power, easily enough to drive most headphones. But there are definitely some headphones that I do not recommend using with the One. In general, these are inefficient flagship planar magnetic headphones like the HiFiMAN HE6, Susvara, Audeze LCD-4, HEDD Audio HEDDphone, or the Abyss stuff. If you’re looking to get into one of these flagship level headphones, you’re better off going for the THX 789 or another more powerful amplifier (likely balanced as well). But I highly doubt anyone with those headphones would be targeting the $200 price mark regardless.

Additionally, the THX AAA One is not for those looking for some alteration to the headphone’s frequency response. Not only is it a more analytic and detailed kind of sound (as opposed to a smoothed over and relaxed sound, or something you might get from a tube amp), it also isn’t something you can use to mess with output impedance synergies. So for example, if you want to boost the bass on a Focal Utopia, which has an impedance bump in the bass that will elevate with sources that have high output impedance, the One is not going to be able to do that for you. Moreover, there aren’t any other analog ‘boost’ functions or features here like you might get with the iFi amps.

General Musings

The One uses an aluminum chassis, and feels reasonably sturdy and well-built - apart from its somewhat cheap feeling buttons. The gain switch and volume knob feels comfortable to use, however, and I have no complaints about the general useability of the amp. There are rubber feet on the bottom of the amp as well, meaning that it’s not going to scratch something underneath it.

For look and feel, the One has the same kind of no-nonsense design that the 789 has, just slightly slimmer. Personally, I like this design. It’s sleek, professional, and my favorite kind of ‘extra regular’. It may lack a bit of flare or contours that others may be after, but this kind of non-flashy aesthetic works well with my general lack of personality, so I’m into it. No distractions from the music or the task at hand!

My main complaint about the form factor is that compared to other budget amplifiers, the One’s footprint is a bit on the large side. Now, for me it’s not a problem, but I can imagine for those who are space constrained on their desks, the One would be a less attractive option. For anyone wondering, the chassis dimensions are roughly 8.5” x 8.5” x 1.3”.

As mentioned, the THX AAA One doesn’t get hot at all - meaning if you live in a hotter environment, you won’t have to worry about extra heat generated from your source. I typically can’t use my Cayin IHA-6 in the summer because it gets way too hot. Moreover, I can’t use it at the bottom of a stack because of the heat output. With the One, this is again something you don’t have to worry about - and it fits in a stack quite well.

Why I Like It

As a headphone reviewer, the THX AAA One is an excellent reference amp that allows me to be confident about my headphone evaluations and measurements on the GRAS43AG. I don’t want to be using a source that’s going to skew measurements in any way. Moreover, as I’ve mentioned throughout this article, the One is more versatile than many of my own personal headphone amplifiers that are meant for different things - like the Cayin IHA-6, which I can’t use with most ‘normal’ headphones that are a bit more sensitive, and I certainly can’t use it w ith IEMs.


While I have a lot of good things to say about the One, it’s also important to take stock of the rest of the budget reference amp landscape. Doing so reveals that its main competition comes from the Schiit Audio Magnius, which is a balanced version of the Magni Heresy, with quite a bit more power output than the One has. The Magnius gives you enough power to drive that last 1% of headphones. But, it’s also important to recognize that balanced is not inherently better than single ended for sound quality. It simply has certain advantages like the potential for higher output. And, given that I prefer the One over the Magni Heresy, I think a comparison between the Magnius and the One is required - and unfortunately I don’t have that amplifier on hand.

Drop + THX AAA One Linear Amplifier Review | Headphones.com


I’m not ready to say that the THX AAA One is the best budget reference amplifier available at $200 - again, because the Magnius exists. But so far it’s the best sounding amplifier I’ve heard at this price, and while most good budget amplifiers don’t sound very different from one another (as long as they actually are good), I do think the One is worth the price increase when it comes to sound quality over the L30 and other budget entry level amplifiers - provided you have the desk space for it. Because of this, the Drop + THX AAA One Linear Amplifier gets my recommendation.


Watch the video review here:



Discuss the THX amps on the HEADPHONE Community Forum.


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