Monolith by Monoprice Portable Headphone Amp and DAC with THX AAA Technology review: High value, minor flaws

This affordable and portable headphone amp will bring out the best in your headphones; but the unit's size, weight, and smudge-prone surface keep it from earning our highest mark.

Monoprice Monolith Portable Headphone Amplifier

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At a Glance

Today’s laptops and smart devices pack lots of performance and high tech. Their audio prowess, however, often leaves something to be desired. The biggest shortcomings typically lie with their onboard amplification and the DACs that convert a digital signal to analog). As audio enthusiasts with premium headphones know all too well, these deficiencies can rob their headphones of peak performance.

Monoprice’s $279.99 Monolith Portable Headphone Amplifier and DAC aims to address those shortcomings while providing gobs of power, an advanced DAC, and adding premium features in a small package.

Meteoric rise onto the audio scene

Monoprice blasted onto the scene seemingly out of nowhere years ago, selling high-value, high-performance HDMI cables. At the time, Monoprice shattered the market held by ridiculously priced HDMI cables.

Thanks to some nudging from audio enthusiasts within the company, Monoprice then launched a line of high-performance, high-value audio gear under the Monolith brand. The Monolith line is geared towards the audiophile and home theater crowd. I had the opportunity to review the Monolith 7, a seven-channel 200-watt-per-channel amplifier whose price and performance left me awe-struck.

The Monolith portable headphone amplifier connected to an iPhone XS. The two are comparable in size. Theo Nicolakis / IDG

The Monolith portable headphone amplifier connected to an iPhone XS. The two are comparable in size.

Since my review, Monoprice’s Monolith lineup has grown exponentially to include speakers, headphones, subwoofers, a Dolby Atmos multichannel preamplifier, as well as desktop and portable headphone amplifiers and DACs.

Beautiful build and styling

The Monolith Portable Headphone Amplifier and DAC is beautifully constructed with a black, brushed metal face; matte black sides, and a back plate with a flush, imitation leather grain that goes almost edge to edge. The unit’s monochrome screen is small but legible. The screen serves as a dashboard letting you know the input, volume, and battery status. If you’re connected via USB, it will show you if your audio source is PCM or DSD along with the source’s sampling rate.

Monoprice Monolith Portable Headphone Amplifier and DAC sports a brushed aluminum front. Theo Nicolakis / IDG

Monoprice Monolith Portable Headphone Amplifier and DAC sports a brushed aluminum front.

The Monolith measures 5.35-inches x 2.84-inches x 0.57-inches (about the size of a typical smartphone) and weighs in at half a pound. There are four physical buttons on the right-hand side for menu functions.

While the Monolith sports a small form factor, it doesn’t mean it’s a practical on-the-go amp and DAC. I found the Monolith a bit cumbersome to carry around in addition to my iPhone XS, and the tangled web of cables cumbersome to use when walking. I’d say this is really intended for someone who wants portability but won’t be moving around when you’re using the Monolith Portable Headphone Amp.

Power under the hood

AKM’s flagship 32-bit AK4493 DAC is at the heart of this device, supporting PCM sources up to 768kHz and DSD 2.8, 5.6, and 11.2 signals.

monolith side buttons Theo Nicolakis / IDG

Detail view of the physical buttons along the unit’s right-hand side.

The amplification side of the device is handled by a THX AAA 788 amplifier module. The acronym stands for Achromatic Audio Amplifier. Achromatic is a Greek word meaning “without color;” hence, THX claims its AAA technology aims to amplify the audio signal without coloration.)

THX’s AAA amplifier technology is known for its linearity and vanishingly low distortion, among other things. I have quite a bit of experience with AAA amplifier technology, having two THX AAA-based Benchmark AHB2 power amplifiers in my reference setup.  If you’re interested in learning more about this technology, you can read an in-depth interview withTHX’s senior vice president of audio research, Laurie Fincham, here. He discusses how AAA was developed and how Benchmark came to adopt it. I don’t mean to imply, however, that the Monolith is a Benchmark AHB2 in miniature. An audio system’s sound is always the sum of its parts. 

The Monolith headphone amp is designed to drive just about any headphone. It will pump out 220mW into 16 ohms, 91 mW into 150 ohms, and 23 mW into 600-ohm headphones. Indeed I had no trouble driving any headphone I threw at it. I should note that some users in online forums have commented about excessive hiss through easy-to-drive in-ear monitors when used with the Monolith.

After extended use, the headphone amp had a tendency to get warm but never hot. I suggest keeping it well ventilated not using it in an enclosed bag.

The Monolith Portable Headphone Amplifier has a 4000mAh battery. I do, however, wish that the Monolith could double as a portable charger, like Oppo’s now defunct HA-2 portable headphone amplifier.

Advanced Features

Features is where the Monolith shines. First up is Dirac Sensaround II. Dirac is well known in the home theater world, developing one of the best room-correction packages available. But don’t think you’re getting some cutting-edge headphone auto-EQ solution when you see the Dirac logo on the side of the Monolith.

Dual USB ports on the bottom allow you to charge the unit and use it as a USB DAC simultaneously. Theo Nicolakis / IDG

Dual USB ports on the bottom allow you to charge the unit and use it as a USB DAC simultaneously.

As deployed here, Dirac Sensaround II is a DSP mode. It’s billed as creating a “vast, clear, and realistically immersive sound stage free from the constraints of the space in your ear, much like a multi-speaker home theater system.” Well, I wouldn’t go that far. In real-world use, Dirac’s Sensaround II creates a more relaxed musical presentation, as opposed to the more forward sensation you get with headphones. The effect is not as dramatic as the marketing folks make it out to be, and you’ll either like it or you won’t.

The Monolith’s inputs are versatile. In addition to the USB input, the 3.5mm analog line-level input doubles as an optical input.

Detail view of the Monolith’s top with 3.5mm input and headphone output. Theo Nicolakis / IDG

Detail view of the Monolith’s top with 3.5mm input and headphone output.

Four additional features elevate the Monolith’s value and practicality:

  1. You have the ability to set PEQ (parametric EQ) to target specific frequencies.
  2. Shelf EQ lets you boost or cut frequencies above or below a frequency setting.
  3. You can change the DAC’s filter speed settings
  4. Dynamic range control lets you set two independent stereo compressors and a mixer to combine the low and high bands.

That volume knob is a two-edged sword

The analog volume dial dominates the unit’s upper right corner. Taking a cue from high-end digital audio players, the volume knob plays a prominent design role. I found it relatively easy to turn with my index finger for left-handed control or with my thumb for right-handed use. Be warned, however, the volume dial is very sensitive.

That will be a good or bad thing, depending on your perspective. It’s good in that you can spin the volume up or down quickly. But don’t dare rub up against it while its in your pocket. Your music will go silent or you’ll throw your headphones off your head as the volume spikes. I had a couple of situations like that when I was just reaching for the unit. I’d like to see Monoprice make some adjustments with the volume knob’s sensitivity or perhaps introduce a volume lock feature. 

monolith volume knob Theo Nicolakis / IDG

A detailed view of the analog volume knob, which is extremely sensitive.


I tested the Monolith Portable Headphone Amplifier and DAC with the Astell&Kern Billie Jean, Aurvana Trio, Bowers and Wikins C5, and Fiio F9 Pro in-ear-monitors as well as the Focal Clear and Beyerdynamic Amiron Home over-the-ear headphones. I used the Monolith as a USB DAC connected to a Mac, and I used the analog input fed from an iPhone XS. Sources included my Roon media server and Tidal.

The Monolith Portable Headphone Amplifier drove every headphone I connected to it with ease. This was most notable with the Beyerdynamic Amiron Home and Focal Clear. Bass control on Shaed’s “Trampoline” or Imagine Dragons’ “Bad Liar” was good, though I longed for a bit more texture.

The Monolith’s rear has an immitation leather grain. Theo Nicolakis / IDG

The Monolith’s rear has an imitation leather grain.

The Monolith delivered siren songs from my pantheon of female vocalists, including Natalie Merchant, Norah Jones, Adele, Dido, Alycia Keys, Laren Daigle. At times, I longed for a bit more presence, midrange transparency, and dynamics.

Generally speaking, the Monolith Portable Headphone Amplifier and DAC is a very good product. In my tests with over-the-ear headphones, the Monolith conjured up the music from a black background. If you’re looking to elevate your computer or smart device’s audio and gain advanced features such as PEQ, it’s something you should seriously look at. But I’ll stop short of calling it a reference product. The device shines with its digital inputs, but the analog input is less impressive. For me, it lacked that last ounce of transparency, involvement, and musicality.

I found the Monolith’s aluminum face prone to fingerprints and smudges. Theo Nicolakis / IDG

I found the Monolith’s aluminum face prone to fingerprints and smudges.

Its value depends how you intend to use it

Monoprice’s Monolith Portable Headphone Amplifier packs a lot of tech in a tiny package, though I’d stop short of calling it practical for active on-the-go use. Built around THX’s superb AAA amplifier technology and AKM’s flagship DAC, there isn’t a file format or headphone that will make this baby sweat. The digital inputs sound better than its analog counterpart.

But the Monolith’s real value lies in its arsenal of PEQ, shelf EQ, filter speed settings, and dynamic range control. Dirac’s Sensaround II will appeal to some and disappoint others. If all those features resonate with you, then the Monolith Portable Headphone Amp deserves serious consideration. If they don’t matter to you, the Monolith’s value proposition drops a bit. Likewise, if you’re in the market for a headphone amp and DAC and intend to use primarily digital sources with it, this one should float your boat. If you think you’ll be listening exclusively to analog sources, it’s much less appealing.

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At a Glance
  • Monoprice's Monolith Portable Headphone Amplifier and DAC will bring out the best in your headphones, but the unit's form factor, analog input, and smudge-prone surface hold it back from earning higher marks.


    • Will drive nearly any headphone effortlessly
    • Features AKM’s flagship 32-bit AK4493 DAC, with PCM and DSD support
    • Outstanding set of PEQ, shelf, and dynamic-range control settings
    • USB, optical, and analog inputs


    • Brushed metal surface easily picks up fingerprint smudges
    • Analog input not as refined as the digital inputs
    • Size and weight make it cumbersome for active use
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