Monolith THX AAA 887 Headphone Amplifier - Official Thread

Monolith (by Monoprice) have release another THX AAA based headphone amplifier, the snappily-named “Monolith by Monoprice THX AAA Balanced Headphone Amplifier featuring THX AAA 887 Technology” at $399.

Extensive specs are on the product page


Along with the THX AAA 789, this is a game changer that brings TOTL performance at a very affordable price. FWIW, it measures a smidge better than the 789:

I suspect for a lot of people looking into solid states, they can simply get this one or the 789 and never need another amp unless they’re chasing summit-fi.


It’s good to see the competition from Monoprice in the THX offerings. It’s even better that it’s in stock and available for purchase. Well done.


The layout/face of the Monolith is pretty near identical to the (Mass)Drop THX AAA 789. Even the ‘special feature’ of a Timed Off is the same. Given that the technical specs of both are beyond human biology, commoditization is rapidly approaching.

How long before this level of performance costs $200? $100? $50?

[The extreme product similarities also make me deeply suspicious of the looooooong delays with the M-D 789 last year. Was there capitalistic monkey business going on per the THX licensing or a critical component manufacturer?]


SMSL sp200 is a thx amp that goes for $289. When it launched was about $270, I believe.

I think Drop’s business functions more like a kickstarter than a typical oem. After they hit a sales target they go into production.

I think the most interesting thing with these THX AAA ### amps is that, given the objective outlook that they’re ALL going to be audibly indistinguishable from each other, their respective manufacturers have decided to approach differentiation from an aesthetics perspective.

Unfortunately, it appears they’re simply trying to progressively out-ugly each other with their industrial designs.


So they all have an antiseptic sound and no musicality? Good to know.

I strongly disagree that the THX products are non-musical or worse than what came before at this price point.

Every time I use a distorting source, I eventually learn to recognize and reject the distortion. This can occur either with cheap/low-end products or very nice products. Distortion can and does sound fine, better, or fun for a while, but eventually becomes a distraction given familiarity with known recordings.


What on earth is “antiseptic sound with no musicality”? I would like to know what this useless cliche stands for. And please, don’t start with you have great ears…

Equipment that distorts changes the signal received. It acts as an instrument.


Which is fine, unless your goal is “raw fidelity”, which is absolutely not everyone’s goal here.

Just one among many different preferences.


I have had the new Monoprice variant for a few weeks now and wrote this first impressions experience over at audiocircle and head-fi:

Well the surprise is out…and I am very happy that my wonderful wife got me this new amp for Christmas!!

Of course I had to open the box when it arrived today to make sure it was functional and I didnt have to return it for any possible defect. So far I have checked all the inputs and outputs for function. They all seem to work as designed, including the balanced and se jacks.

So why did I decide to get this particular amp, JohnR, one of the circles admins, started a thread about the THX AAA amps, and I really have not kept up with all the new technology out there, so as I was reading what Schitt has done to help solve the Class AB crossover distortion with their continuity implementation in the new ASGARD 3 and other amps, I learned that THX was working on this issue as well but with higher power speaker amps.

I watched and listened to a video with Laurie Fincham, who is Vice President of Audio Research at THX. He describes a 9 year process that led to this new THX AAA or Achromatic Audio Amplifier. In the video the focus is on the work of THX with Benchmark and the development of the Benchmark AHB2. The neat thing about this gentleman to me is he is an audiophile, engineer, music lover and a musician. So the background is he speaks to the Class A amp classification as “big, expensive, beautiful , but hot”…this again was focused on large 2 channel amps, but the parallels are there for Class A headphone amps. There are a few Class A amps that you can almost fry an egg on!! (can you say Asgard 1).

So they didnt invent or re-invent the amplifier but as he states, they looked at the shortcomings, the physics, and developed a technology to deal with these. They have been working on this since 2006. The result is an amplifier that stays within a fraction of its low distortion right up to 1db of its full output. Distortion in the Benchark amp was about 100x lower than was seen with existing amps and the S/N ratio is much higher. Another interesting part was for them to measure this new technology it turned out to be very difficult, and they only felt they had the correct or accurate result when at least three engineers using three different sets of measuring equipment “got the same answers”…

So they claim this technology provides a “clear window to the music”. The aim of keeping the signal clear and pure was the inspiration for the new technology, AAA or Achromatic Audio Amplifier". Achromatic means “without color”. The proverbial straight wire with gain.

For more info on this you can Google THX and Laurie Finchman and oh by the way he played the string bass in a band for 17 years.

So this is the reason I bought this amp, its a technology leader and has some of the best measurements ever to date. The techie in me had to listen with this new amp and its technology for myself.

So how does this technology stack up for us headphone folks…one word: “EXCEPTIONAL”.

I have had only six+ hours with the amp, and it doesnt take me long to know this is a really special amp. The magic in short is THX measures the distortion as the signal crosses the Class AB + to “0” to - swings…and inverts this and re-injects it to cancel this crossover distortion…voila distortion gone (or negated). But there is more to this than just that…as always, great design and layout, power supply, low noise intergrated circuits or op amps…as the 9 year adventure evolved the quality of ICs and IC’s designed and produced specifically for headphone audio amps appeared.

The sum of all these parts can make or break anypiece of gear and make it a stellar device or just another run of the mill device with all sorts of claims of audio nirvana.

New gear"itis" is always an issue, so I want to really be sure I am hearing what I think I am…so I brought over some friends and my most severe critic my wonderful “wife”…going back and forth eveyone liked the immediate “clarity” of the amp…comments like “gosh those guitars sound so clear, that drum sounds so much like a real drum…her voice is magnificant”, “hand c;aps that sound like a human being made them”…and most of these folks were not audiophiles and think I am abit strange with all my audio stuff!! I did some blind AB switching and asked everyone which one is “better” to them and why, and then which one was more clear…all but one picked out the THX amp over the other (won’t mention this one …but its a favorite here)…

So my first impression is this amp is so dark, or quiet…total silence, you dont know its on, across all three gain settings with the volume turned up all the way. Its a brutally honest amp, it lets you hear how good or bad your source is, its all there…you can easily discern music quality, compression etc…the often over used “garbage in garbage out” is here in spades! (in my second listening session, hour 7 I am up at o’dark thirty when the ambient noise is very low…I do detect a very slight hiss at high gain with 55 ohm Clears at the extreme position of the volume knob…in what I call never, never land…the your going to ruin your hearing land).

If your into specs well, they are indeed very, very good. You can take a look at the monoprice site or the charts I posted below. These will make the measurebators out there grin from ear to ear…I might note there are (2) versions of this amp, one from and this one from Monoprice. $399.

The battle for specs never seems to end, how low can you go and for what price (note the recent Schitt Magni Hersey $99 op amps). Well Monoprice went and outdid the Drop version by a small amount but enough for bragging rights!! :>) At least with the Monoprice they were available and didnt have to wait for the Drop etc…The folks at Monoprice indicate they looked at the competition and changed out many resistors, op amps to the 888 level and a few other things to glean a 2db advantage over the Drop version)…I know “crazy” but I like it… :>)

Power, oh gosh, more than enough!! 16 ohms: 8800mw, 32 ohms: 6000 mw, 300 ohms: 700 mw…balanced. Less for SE. I used both no issue at all for low to high impedance T1’s. Is there a difference between the two, to me not much if anything.

The unit has a soft on/off switch, no mechannical click, it starts a on/off sequence and the power led shines red then green then white. There is a mechanical push button switch for selecting balanced or SE inputs, so if you have a balanced dac your good to go. Three position gain switch, .66x, 2.0x, and 6.6x. 1 for IEM’s, 2 for most headphones, 3 for those really hard to drive cans. The output impedance is less than 0.05 ohms! The freqyency response is ruler flat…really flat…crosstalk -127db at 300 ohms! This is the world of a distortionless amplifier…or so dang close its not funny…spectacular engineering IMO.

Absolutely no audible clicks or pops turning the amp on and off with the headphones plugged in. Headphone jacks are XLR 4 pin, standard 1/4 SE phone jack and the smaller 3.5mm SE. Very nice.

It weighs about 3.5 lbs, runs cool, hard to tell its on…class AB…there is a switch on the back that is a byass function or a switch that aftere 2 hours without an input signal the amp turns off, the bypass is there if you want to leave the amp on all the time etc. Build quality is good, the only small issue I have is the volume pot is small and I am wondering how well it will last over time, but the warranty from Monoprice is “3” years…with my useage I will find out within a years time. The low end tracking on this unit is spot on, listening this morning at low levels I can not detect any mis-tracking at low volume levels. I have had to replace a few pots in my DIY stuff over the years for scratchy and mistracking, my ODA and BH Crack. Low level listening is very nice as well.

So more on how does it “sound” or “not sound”. I am trying not to be over-hyped but this unit is really that good…its a blanking really good amplifier, it “draws power to amplify the music signal without imparting any coloration or distortion”…this is a big claim, but it is the closest I have ever heard to this goal. Its alot like other experiences with other amps…you dont want to stop listening…but this is a new higher level. I would say this amp removes the “veil” once again…it allows your headphones to really shine according to their design. What do I mean by that…my Focal Clears I really love, now they shine even brighter…in that they are producing what the recording has in it and to the best capability of the headphone. Its like hey I just got a new set of headphones…my Beyer T1s’ and HD600’s never sounded so good. Live performances like Tom Petty and the Heartbreakers, The Live Anthology, Eva Cassidys, Live at Blues Alley, Sarah McLachlin, Fumbling Towards Ecasty, you can tell what the audience is doing, their reactions, just marvelous. The black background allow you to hear the drum swish’s often overlooked or lost in a lesser amp. Patricia Barber has really well recorded and mastered stuff where she speaks and in between her diction you clearly hear the background instruments playing very subtley…and the room re-verberations. On early Beatles recordings its like your in the room with the “Boys”! Coupled with the Focal Clears its the best I have ever experienced and thats saying alot!!

This amp just makes everything else better for me.

At first one might think this amp is too thin, or bright, with no real weight, but as you play several tunes, you realize the tunes your playing are not perfect and vary all over the place, and the coloration of other amps does change the sound and the experience…this amp is brutally honest. Its ability to let small micro-dynamics thru is uncanny…Chet Atkins, Picks on the Beatles, “Shes a Woman” is a superb example of this…3 dimensional and the really in the background sounds are articulated well…

Some will love it and others will not…thats ok…this is about as far away from a soft tube amp as you can get. We can discuss that specs are important or not, do they make this amp as good as it sounds?? I honestly dont know, all I do know is as I listen to the music I am smiling alot…and this is good!

So what I am going to do is to start a comparison rotation and see how that goes…I also want to try out several dacs, for the first time I have an amp that will not get in the way and allow me to more objectively hear what the other pieces in the chain are doing or performing.

Right at this stage with now 6 hours of play, would I buy this again: Answer: YES.

Smiling again


Let me also add even though this Monoprice version is very much like the Drop version, there are a few things that might influence your buying decision:

The warranty is 3 year at Monoprice and only 12 months at Drop as far as I know.
The circuit compoments in the 887 were changed to the 888 op amps, 5 of them.
50 or so resistors and caps were upgraded to reduce “johnson noise”…

Now granted this only got the a 2 db increase in some measurements, but it gives them bragging rights!

Now, that said the 3 yr warranty IMO is the deal breaker here for me…and I have already used it!



Excellent review. Glad you’re enjoying the new amp. :+1:t4:


@Torq, You have NOT answered the question dealing with “antiseptic sound”.

In addition, any distortion to the signal modifies what the musicians and/or the producers intended for you to listen. However, if you want to make your own music, you can distort as much as you want.

Please, also clarify for me “raw fidelity”. Does this go against “cooked fidelity”? What does the term raw mean in your context? It is like “sushi fidelity”?



I wasn’t aware I was required to; it wasn’t my comment.

I said nothing more than that on objective grounds, all these THX AAA ### amplifiers should be audibly indistinguishable. I made absolutely no mention as to what that might be/how they would “sound”, merely that you shouldn’t be able to distinguish between them by ear.

It means nothing more than “fidelity above all else”.

As does every single other person that listens to recorded music.

Most of them just don’t want to admit it.

Anything else is just quibbling over how, where and why you want to allow deltas.


I almost literally “rolled on floor laughed” at this! :rofl:

:thinking: Seriously we need better looking amps and DACs…I’m a fan of the simple yet elegant JDS Element/El amp, or even just throw on a meter or led measurement…adds a nice flair and set you apart…or even go retro chic like the H.A.L. Amps and DACs (RNHP &Fidelice) Lol :face_with_monocle:


Well, really, the aesthetics here (which I appreciate are 100% personal) are not doing these products any favors - for me.

The Massdrop/Drop version is, I think, the prettiest, but it’s pretty damn tinny and clacky in its construction … especially the push-buttons. The Monoprice/Monolith “feels” a bit better, but manages to look very cheap in person. The SMSL version looks like a donut-tester sat on it and it didn’t fare too well …

John has very nice aesthetics in his Element line.

That “H.A.L.” thing is perfect!

Personally I think the Fidelice line looks a bit naff. Not bad, but definitely doesn’t appeal to me aesthetically (the Precision Headphone Amplifier looks a bit better than the original RNHP … but that had “panel” gaps only a Trabant owner could be proud of).


I am listening right now with my second Monoprice 887 amp…just a few minutes so far…and so far so good. I will tell you why this is number 2 in awhile…no big deal.

That said compared to my other amps. Bottlehead Mainline, Crack, Magni 3, Burson Fun, and several more the 887 is an immediate OMG amp to me…its like having lightning in a bottle good…

Easily discernible with Focal Clears…“raw” fidelity…musical and tonality…100% accurate to me.

I was without this gem for 5 days while I swapped out the original with no real issues but a concern with some hiss I was hearing at extreme volumes, which I wanted to be sure was not an issue just a design end point or a corner case in the test world. The second amp has the same hiss issue as the first, again no-one in their right mind would listen to these high volume settings/

As in my experience posted above as soon as I hit play I immediately smiled and there was that world class presentation I was missing for those 5 days.

All my other amps are great as well, but this new THX version is indeed very special.

The Monoprice is missing from this pix as well as several other diy amps…



Stanley Kubrick was a genius. :nerd_face: