White Noise

Extremely Neutral, Clean Amp
Pros: clean, low distortion, multiple gain settings, good complement of outputs
Cons: zero character
After picking up a pair of Audeze LCD-X, I wanted a neutral amp to drive them with. I looked around in the $200-$500 range and came away with a few choices, and I ended up going with the THX AAA 789 from Drop. If you’ve read prior reviews of mine, you may already know that I primarily work on music with my headphones, so while a pleasant experience is a nice bonus for me, a brutally honest presentation of my music is most important. If my listening chain is making my music sound better than it actually is, I risk stopping work on it when there could be more for me to do in terms of balancing it for playback on other systems. So, with THX’s stunningly low noise and distortion numbers, and the relatively flat sound compared to most of the competition in the price range (according to the research I did, at least), I decided this was the right amp for me. I have to say that I got more than I bargained for.

My first impression of the amp was that it was “fine”. I liked the multiple gain settings for precise volume control. I monitor really quietly, so I use single-ended ins and outs and I’m still around 1/3 volume on gain level one. I liked that it had a nice volume knob with well-matched channels from top to bottom, but the sound didn’t blow me away. I've had the amp almost a year now, and I've added a Schiit Modius as my DAC since getting this amp. And still the thing that I think whenever I sit down and listen to this system is that the sound of this amp and dac, never, ever, wows me. The system really gets out of the way and lets me listen to music, to a fault for most people. If you listen to anything that isn't well recorded and mixed, you may want to look elsewhere. But there is a reason I love this amp...

So, underwhelming first impression out of the way, I kept listening to it in the background as I worked for an afternoon, and then, after a few hours, I took the headphones off and it hit me: I’d been listening for HOURS straight, and my ears didn’t feel it at all. It felt more like I’d been listening for 45 minutes than a few hours. The thing I didn’t hear, but could absolutely feel, was how little distortion there was in the chain now.

I should explain: in pro audio, one of the things that is accepted to determine how much a monitoring system is going to fatigue the listener is how much distortion there is, especially between 1 and 3khz, where the ear is most sensitive. This is such a big deal that, even though 3-way speaker designs are significantly more expensive and don’t offer much, if any, more bandwidth than 2-way designs (since bandwidth is limited more by size than by driver count), they are highly prized over 2-way monitors. Because 3-way setups, even with an extra crossover and more complicated amps, have much lower distortion in that critical frequency range. It comes up in 3-way monitor discussions over and over, and everyone says you have to hear it to believe it. And time after time, people who doubt the cost will be justified use these things and are blown away by how much better their ears feel at the end of a day. Well, I was just blindsided in the same way by a headphone amp. This is the real WOW factor in this amp for me.

So, in summary, the amp sounds fine. It doesn’t make the same difference that a great set of headphones makes, absolutely get your drivers sorted first. And, I wouldn’t expect this to make a huge difference for most people even if you do already have headphones you love. I think if you want a specific sound to your amp, the Drop THX AAA 789 really doesn’t bring any character to the table. But, what it did do for me is take a headphone that already is easy on the ears in long sessions and make it even gentler on my ears, and give me the slightest bit more detail while it was at it. For my purposes, that’s A-OK.
Much better than that hawaii bad guys review. Sounds about right, it's a good amp for the money.
IMO drop should revert back to an opamps design just for an opinion and add a delta sigma dac to match it.


Reviewer at hxosplus
The King of Transparency and linearity
Pros: - Benchmark transparency and linearity
- Still very enjoyable
- Powerful
- Fully differential
- Three output plugs
- Three gain settings
- Suitable for sensitive iems
- Excellent build quality
- Runs cold
- Minimum power consumption
Cons: - Lack of holography
- May sound flat
- Could do with more dynamics
Curiosity killed the cat as they say and in my case it was a great one to experience the Drop+ THX AAA linear amplifier so i have asked for a loaner sample in order to review it.

Drop+ replied and they have kindly provided a long term loaner unit in order to test it and keep it as future reference never asking for a favorable review.

As always this my subjective and very honest opinion that I would like to share with the Headfi community.


No introduction is needed as this is one of the most talked and measured amplifiers in the hobby caught in the middle of the long going debate between subjective and objective performance.

Let's find out together after the brief technical and physical report.

Technical specifications

Announced at CES 2018, the Drop + THX Achromatic Audio Amplifier (THX AAA™) 789 is a linear bipolar amplifier with feed-forward error correction.
It’s designed for objectivists who appreciate an incredibly clean, transparent amp—the sought-after “wire with gain” whose amplification is wholly uncolored by a sound of its own.
Made in collaboration with THX Ltd., it features the company’s groundbreaking THX AAA and feed-forward topology, which reduce distortion by 20 to 40 dB for realistic, fatigue-free listening.
In fact, this bridged-output amp’s performance figures speak for themselves -
It’s powerful (2 x 6W at 32 ohms) and quiet (136 dB SNR) with a record-low THD of -140 dB at 300 ohms, 100 mW.
That’s four times the power of the Objective 2 amp, for example, with far less distortion.


Capable of driving any headphones, including high-impedance, high-current, and high-sensitivity types, the THX AAA 789 amp transmits the original audio in its purest possible form.
That’s thanks in large part to THX AAA technology, which reduces harmonic, intermodulation, and crossover distortions.
Virtually every conventional amplifier distorts significantly when driving current into a headphone, producing crossover distortion that fatigues the listener.
The engineers at THX set out to solve this problem—and to deliver the performance of a class-A amplifier without the heat and weight.

Each channel of the THX AAA 789 amp is equipped with a low-bias class-AB main amplifier and an auxiliary error-correction amplifier, the former providing the majority of the power and the latter providing a realtime low-power error-correction signal.
These work together to null all distortion components.
Additionally, the product’s low quiescent current minimizes wasted power.
Finally, the THX AAA 789 has multiple gain level settings to optimize for headphone and earphone listening.

People keep asking if the amplifier is fully balanced so we are quoting the chief engineer Andrew Mason:

“The signal path internally is fully differential throughout but is NOT truly balanced in a few sections. We preserve the full signal integrity but we avoid increasing the retail price for no measurable benefit.”

The unit itself is a rather compact one measuring 210x230x57mm and weighing 1520gr.


Full specifications are available here -

High-grade CNC-milled aluminum with black bead-blasted finish is used throughout and the build quality is excellent without hard edges or assembly gaps.
The appearance is minimal and follows the Drop+ design pattern which we like a lot.

The pot movement is very smooth and stiff enough to offer accurate adjustment.
The gain control switch is sturdy with good handling but the two buttons are a little loose to the push action.

In the faceplate from left to right we have the power on/off button , the 4-pin XLR output , the 6.35mm and 3.5mm outputs and then the gain switch , the potentiometer and the input switch.

The gain switch has three settings and the input switch is to choose between single ended and balanced inputs.

That gets us to the back where we can spot the single ended and balanced inputs plus a single ended pass through output.
A switch is used to switch between bypass and auto off modes.

The amplifier is powered by a universal switching power adapter with a rated output of 24Volt/1.8A.


Listening set-up

In order to be sure about the amplifier performance we have employed all our arsenal consisting of various headphones / iems and DACs in balanced and single ended configuration.

We have cycled between the Denafrips Venus mkii , Pontus , the Cambridge Audio 851N and the SMSL M100 mkii.
Headphones included Meze Empyrean , Sennheiser HD660S and 650 , Drop+ HE5XX , HiFiMan Ananda and others plus a couple of iems like the FiiO FD5 and the Meze Rai Penta.


Can you handle the truth?

Let's cut straight into the chase.
This is the most linear , balanced and transparent amplifier we have ever tested till now.
There is an absolute lack of character or any kind of extra coloration just a brutally honest amplification of the incoming signal.

The AAA really shines by its absence just to make sure that the only character that is delivered to the output is coming from the source and is up to the headphone to translate it into sound.

As that is ruthlessly revealing of the recording quality so if the rest of the chain is equally flat then a lot of familiar stuff may start to sound bad.

Matching the amp is not the case here because it is literally out of the equation and we only have to worry about DAC with headphone pairing.

Nothing gets in between and rest assured that if you love your headphones and DAC then you are going to further adore them but if it was some kind of a lukewarm relationship then be prepared to reach for the classifieds.

Don't let the price fool you as the THX AAA is not afraid to be paired and do full justice with the most expensive DACs and headphones available at the market and is going to highlight the best and the worst parts equally.
The THX AAA is the perfect tool to highlight the differences between various DACs and helps to further understand and at the end enjoy the various sound flavors plus it further helps to hear and appreciate the exact tuning of every headphone.

Clarity is crystalline like spring water pouring in the high mountains and that is for the whole frequency range.
Background is totally black and the noise floor is inaudible so all the available detail is exposed but served in a polite and effortless way rather than being pushed into us.

Every last note is heard even in the most dense passages and all instruments are carefully placed with pinpoint accuracy and perfect individuality without masking each other.

Sound is tight and lightning fast with all the extension you could wish for in a well organized presentation without hard edges or any kind of brightness.

The AAA is not lean sounding but don't expect it to add any extra weight to the sound or alter the decaying time of a given headphone.
So lean headphones will sound lean and full bodied headphones will sound full bodied.
As you can understand this is not the kind of amplifier that we can use to fine tune our headphones.

Power is not an issue and from the balanced output the THX AAA can drive with ease and authority almost all the headphones out there.
As for distortion , well this is an unknown word and the headphone is going to reach its limit first.
Driver control is excellent but it is not the most hard hitting and slamming amplifier especially compared to some special discreet designs.


Is it for the pro market?

So by now you have been probably left with the impression that this is the professional kind of amplifier that sounds boring , cold , sterile , metallic , soulless and all the usual adjectives that are used to describe such amps.

Well in our case this is far from the truth because the THX AAA strikes the perfect balance between transparency and enjoyment.
The amplifier sounds very engaging and organic with great overall timbre and all the available harmonic richness at least as it is passed through the source.
We have greatly enjoyed all our listening sessions with demanding classical music and the amplifier was a great partner with all the headphones used with surprisingly good synergy with the Empyrean.


So is this the perfect amplifier?

Well nothing is perfect and as noted above there is a certain lack in ultimate dynamics and we could surely do with some extra body and roundness as the notes sound a little thin.

Then while the time domain is rendered with good cues of echo and reverb there is a certain shortcoming in space allocation.

Although instruments are surgically placed with excellent pinpoint accuracy and definition the stage is a little bit constraint width wise and there is not enough room available to breathe out.

Combine this with the minimal depth layering and we are presented with a wall kind of sound that is short of holography.

Smart matching between DAC and headphone can help a lot but some combinations will sound flat.


I don't care about balanced set ups

Luckily for you, Drop+ has recently announced the little brother of the THX AAA amplifier, the brand new THX ONE linear amplifier.

Priced even lower at $199 is a single ended design with the same technology and capable of some serious power of 1500 mW/16 ohms, 2700 mW/32 ohms plus a new preamp output.
You can read more here - https://drop.com/buy/drop-thx-aaa-one-linear-amplifier.

At the end

The Drop+ THX AAA lives up to the hype and it is a true high end reference amplifier with ultimate transparency and powerful enough to handle everything we throw at it.

For $299 it is competitively priced and it is very highly recommended not only because it is the one of the most linear and excellent measuring amplifiers but first of all because it sounds very engaging and enjoyable.

This is an amplifier that should be part of every hobbyist collection not only for it's sheer musical enjoyment but also as it is the absolute measuring instrument to judge performance of headphones , sources and other amplifiers alike.

Full playlist is available here - http://open.qobuz.com/playlist/5669033

Copyright - Laskis Petros 2021.
I guess it should work.
Give me a couple of days to test it with Schiit Vali 2+
What are lean sounding headphones? Your assertion that an amplifier does not affect the sound of a headphone is laughable. Try DCA Aeon to hear headphones that have changes in decay, etc depending on the amplifier. Objective? Denial is not a river in Egypt my fellow human being.
First of all try to become more polite.
Then I might answer you.