Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC
Michael Piskor 2019

Monoprice Monolith THX Portable Headphone Amplifier & DAC Review

This is a review of the new portable Monoprice Monolith THX Portable Headphone Amplifier and DAC featuring THX AAA amplification technology. It is priced at $299.

Disclaimer: This is a sample sent to us in return for our honest opinion. Headfonics is an independent website with no affiliate links. We thank Monoprice for this opportunity.

To read more about Monoprice products we have previously featured on Headfonics click here.

Note, that this article follows our latest scoring guidelines which you can read up on here.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC
Monoprice Monolith THX Portable Headphone Amplifier & DAC Review
The build is perfect, it is exactly what I want physically. The LCD and UI are lovely, all be it, a bit clunky, but still easily traversed. The power output is very good and apart from the most absurd Planar's out there, this Monolith can drive anything I tossed at it perfectly fine.
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Reader's Score

For my third installment of Monoprice goodness, in recent weeks, I’ll be taking a gander at the Monoprice Monolith Portable THX AAA DAC and Amp! I have a lot to say, so let’s not waste too much time on here for the intro. Big thanks to Marcus, again, for making this review possible. Thank you!

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC

Accessories & Packaging

The Monolith box is fairly basic, just thick cardboard with an adapter and USB cable for charging. No interconnects are included, which bothers considering the $299 price point. If this product uses both 3.5mm and optical input, then it should come with at least a very short interconnect for both.


I am sad to see that it does not and that I have to fish out some other brands interconnects for this review. I really dislike the idea of not being able to immediately use the product when consumers purchase it. Cables should always be included. No and’s, if’s or but’s.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC


Dear cosmic deities! The build on this is absurdly great. Solid aluminum framing with an LCD window, monochrome, but still, very vibrant and lovely. The front panel looks like brushed metal, the rear side houses an imitation leather material.

I am not sure I like the combination, but I see why the rear has that material: due to laying on surfaces most of its life, sustaining damage or scratches will be unlikely with a covered material on the rear. However, the front side is very prone to fingerprints and damage in that regard, so, I am not sure what to make of it.

The buttons are solid and have no wiggle, they exude excellent cosmetic flare and also a dense feel. The volume knob is the star of the show, with a twisted metal vibe and a thick, weighted feel to the experience.

I am a bit scared to keep this in my pocket though because the step attenuation is extremely sensitive and you can go from -20 to +10 very fast and suddenly if you brush up against the volume knob.

Maybe, a simple firmware can stop volume hikes? Just a thought for the future. There is no question that this Monolith portable amp & DAC is a monster in terms of build. It oozes supreme quality from top to bottom. Lovely.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC

External Features

This Amp/DAC sports a simple 3.5mm output for headphones, as well as a 3.5mm optical/line input on the top of the device. Directly next to them, lays the hefty volume knob that I enjoy playing with often due to high and satisfying tactility factor.

Down the left side of the device, you get a Menu button, manual scrolling up and down buttons for cycling through the UI, and lastly, a select/Enter button. The underside of the product showcases a charging port and a USB connection for DAC usage.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC

Internal UI Features

This product is loaded with a fantastic internal UI, although, it is confusing at first and requires some usage to nail the layout after playing with it a bit. It includes a dynamic EQ system, fraught with plenty of customization options.

The UI window will show every single step of volume with the twist of the knob and will shut down the UI window view via twisting the volume knob far to the left, the reverse to turn the unit on. In terms of matchability, this product is nearly perfect.

The fact that a $299 DAC/AMP allows for digital control over some shelf-EQ, is a blessing in its own right. Ignore at the moment how good it sounds, just focus on the fact you even have one in the first place.

True, the UI is a bit clunky, but it’s very basic still and that is okay by me. It gets an epic pass for the inclusion of an actually functional EQ system that, well, actually works and sounds audibly different when toggled.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC


I am not a fan of the new AKM4xxx series. It is always hit and miss and not consistent in quality. It is very picky with selecting parts that mesh with it and that is where the designer takes over for quality needs.

The people designing and implementing the physical layout of THX products are doing such a great job, that I want to meet them and just talk about how great they are. They’ve been absolutely slaying it lately. 2019 is the Year of THX. Nobody can argue this.

They’ve dropped in an AKM4493, which I, again, am not fully fond of. But whatever other parts are in there, mesh well with it and make it sound fantastic. The THX AAA AMP circuit is also very quiet. Well, scratch that, it is dead silent and shelves no noise what so ever on mute.

PC DAC Usage and External Amp Pairing

When used as a PC DAC, the experience at $299 is phenomenal. In fact, I am going to call this the best small DAC in the entire market. Period. When I run high-end DSD tracks through this and Foobar2000, with selective DSP that I favor, I am just stunned at how great this product sounds.

Considering it is so small, it is right up there with the likes of the over double the price Hiby R6 portable music player and has beaten SMSL’s full-size DAC I reviewed earlier this year entirely, which is the same price as this THX AAA portable unit from Monoprice.

I often hike up the bass quite a bit for usage with some bass centered headphones and in this case, can’t use the internal EQ of the THX. S

o, I route through the music app and the experience is only lacking a density factor that I find in the R6 and some other high-end DAC’s. Beyond that, the overall fidelity and immense response to EQ are sublime.

EQ Preamble

Response to EQ is important. It is like being stuck with what the track offers or what the product offers stock. I want options.

This is like buying a car and only be able to drive it on a nice sunny day on a perfect road. I want to buy a car that has excellent windshield wipers and can safely traverse a highway at 60mph in the rain and if need be, trail up a hill with traction control.

My point is expensive specialized products are not good for consumers, they are good for specified audiophiles who have other gear to cover other types of listening needs. Response to EQ fixes this and allows me to enjoy neutral when I want it, or musical when I want it.

I want a great EQ response, which means moving the dial-up just a bit and hearing a difference. Feeling a difference. Overall, the end result is audibly different in a positive way.

This product offers that both off of DAC usage and with a portable music player attached, or through the DAC + PC usage. Options are lovely.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC

Sound Impressions


In stock form, without any EQ function active, the THX AAA Portable Monolith is a neutral beast in terms of tonality and physicality. The experience is flat and I would even call it lacking in quantity.

There are bassy headphones I have tested with, such as the Blon Planar headphones or the Audeze GX, that I consider somewhat bass capable, that sound underwhelming in physical quantity.

Quality aside, which is fantastic, the physical quantity is less than what I could consider them to be with some other gear I have but it doesn’t matter because the EQ functions let you dial in some extra without sacrificing any quality.

I was able to reach an absurd +6db before I feel some shake on the bass. That is a lot of additional bass before it begins to audibly falter. When paired with a very warm source, the portable experience is altered a bit, so that means once again, matchability is superb. You can rig a pair with this and change the outcome to your liking.

If you have very neutral headphones and source players, the THX here will sound very neutral. If you have very warm and musical headphones and sources, the THX here will sound more musical than most.

Thankfully, bass kick and slam is never an issue. The unit is moderately reserved in that regard and neither kicks too hard or too soft.


The Monolith chimes in with a solid and engaging sounding product here, definitely more forward than the OPPO HA-2 and certainly more forward than any of the Xduoo or FiiO amps that I’ve come across lately.

This pairs wonderfully with my Audio Technica and JVC mid-centered headphones, it doesn’t play so well with the HD800 from Sennheiser, but that is only in regard to the physical setup in the midrange.

Everything else sounds great. Very relaxed and recessive headphones tended to sound a bit too relaxed for me, lacking engaging qualities in a presentation locale manner of speaking. With that in mind, the fidelity factor is off the chart good for $299.

I don’t think it is that far off from something like my older Astell and Kern players from a few years ago, nor the Hiby R3 and AP80.

Midrange Density and Heft

Swapping between the Hiby R6 and the $299 Monolith portable, using the same headphone, results in the Monolith sounding noticeably thinner and less hefty. It really isn’t at all a problem, because I consider the Hiby DAPs to house excellent density and physicality.

The fact that the Monolith by itself can do what it does and sustain good heft, is impressive. It looms on the same playing field as the Hidizs AP80 in that regard, and that is a great quality. Density factors are overlooked by many audiophiles and I am one of those listeners who demand solidity and a marble-like feeling to the entire presentation.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC


The top end is just a bit bright, I don’t consider it to offer a sense of neutrality and flatness, even on a flat or absent EQ set. I don’t think it is “boosted”, per se. Rather, it just offers a good sense of quantity without going overboard.

I would EQ the top-end shelf down just a tad if you have treble-happy Grado’s or very harsh and clinical-sounding headphones in general. Otherwise, you will be just fine. The response to EQ is excellent, you can drop off or add more if you want as desired.

I am just a little unfond of the physical strike impact, as swapping between it and the R6 DAP showcases the R6 to offer a softer top-end performance. The dynamic kick factor is more prominent on this Monolith.

Again, I wouldn’t call it bright, but it is just audibly so, at least, compared to the more streamlined bass experience. The top-end pokes out a bit and that isn’t a negative plot point at all. It lends credibility to the imaging factor offered.


The Monolith Portable here is easily the widest and spacious sounding DAC/AMP in its price point and body style. Of the smaller, more portable DAC’s and AMP’s out there, this is noticeably superior.

In fact, it is audibly superior to my Hiby R6 using the same headphone and track. When the R6 is plugged into the Monolith Portable, the experience is superior in vastness and spaciousness than when I remove it and connect directly to the R6 with my headphones. That is stellar and then some.

This is a sound stage titan. If you want excellent imaging in every way, this is probably the best I’ve ever heard on the market. I don’t own any other smaller portable-ish product like this that sounds anywhere near this coherent, nor anywhere near as vast overall.

Height, Width and Depth of field are all excellent. The air factor is sublime, which is lent some help through the plentiful treble experience offered. No doubts here, as a soundstage nut bar, this is one of the best I’ve ever played with for sound stage needs.

Monoprice Monolith™ THX® Portable Headphone Amplifier and DAC

Our Verdict

Monoprice is absolutely destroying the competition this year. They seem to be aiming for the sky, or space, or something. Each product gets better over time and they aren’t likely going to stop any time soon. In a few years, I can’t wait to see what the THX tech can do and provide for me if this little Monolith can achieve imaging on that absurd of a level.

The build is perfect, it is exactly what I want physically. The LCD and UI are lovely, all be it, a bit clunky, but still easily traversed. The power output is very good and apart from the most absurd Planar’s out there, this Monolith can drive anything I tossed at it perfectly fine.

The price is right, the style is right and the sound is hyper-customizable. This is probably the best overall portable solution I’ve ever come across.

Monoprice Monolith THX Portable Headphone Amplifier/DAC Specifications

Model 24460
Amplifier THX AAA™
Inputs 1x unbalanced 3.5mm TRS, 1x Optical, 1x USB
Playable Frequency Response 1Hz ~ 20kHz ±0.5dB
Signal-to-Noise Ratio (A-Weighted) > 117dB
Dynamic Range > 117dB
Total Harmonic Distortion < 0.001%
Crosstalk < 100dB
Total Output Power Single-Ended (mW)
16Ω 220
32Ω 340
150Ω 91
300Ω 46
600Ω 23
Maximum Output Voltage 3.7 Vrms
Maximum 3.5mm Analog Input Voltage 2.0 Vrms
3.5mm Analog Input Impedance 10 kilohms
Optical Sampling Frequency 32 ~ 96 kHz
Maximum Optical Resolution 24 bits
USB Sampling Frequency 32 ~ 192 kHz
Maximum Coaxial Resolution 24 bits
Direct Stream Digital™ Support DSD64, DSD128
Battery Capacity 4000mAh
Charging Power 5 VDC, 2A
USB Wall Charger Input Power 100 ~ 240 VAC, 50/60 Hz
Dimensions 5.4″ x 2.8″ x 0.6″
Weight 0.5 lbs.

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