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Review and Measurements of Monoprice THX Desktop DAC & Amp

amirm

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#1
This is a review and detailed measurements of the Monoprice THX AAA Desktop DAC and balanced headphone amplifier. It is on kind loan from a member. It costs US $480 from Monoprice direct including free shipping. The only other desktop headphone amplifier with THX AAA amplifier is from massdrop and it doesn't have a DAC, nor is it easy to find. So if the Monoprice performs, it will be a major win seeing how it also includes a DAC for only $80 more than Massdrop.

I previously tried to measure this unit when it first came but unfortunately it failed on my bench.

The industrial design is good:
Monoprice THX Desktop DAC and Balanced Headphone Amplifier USB Audio Review.jpg

The display looks a bit grainy to my eyes but it does the job. What doesn't is the volume control. It is digital which is fine. Not so fine is that it runs way behind the volume knob if you turn it quickly. You can literally take your hand off and watch it keep going for a few seconds. And it is not just the display: the volume adjusts in sync with it meaning if you play something quite loud, it may take a while to get the volume down. The logic for this needs to be modified in the firmware to skip values when the knob is turned quickly (i.e. have acceleration).

Sadly there is no remote control.

Here is the connectivity:
Monoprice THX Desktop DAC and Balanced Headphone Amplifier USB Back Panel Audio Review.jpg

It is always a pleasure to see balanced inputs to get around potential ground loops. Inclusion of AES/EBU (XLR) digital input is also helpful in this regard.

I am sure you all are interested in measurements so let's get into them. There is a ton here as I had to measure the unit both ways: using digital USB input and then XLR analog input.

DAC Measurements
For this test, I manually set the headphone output to 2 volt, not realizing until later that there is a fixed mode setting in the menus. Regardless, I think this is close enough to not merit re-measuring it:

Monoprice THX DAC and Balanced Headphone Amplifier USB Audio Measurements.png


Second harmonic distortion is at -120 dB. Since out SINAD is at much lower -- 107 dB -- it indicates that there is fair amount of noise to reduce performance that much. As it is, the Monoprice THX desktop falls in second tier of our performance ratings:
Monoprice THX DAC and Balanced Headphone Amplifier USB SINAD Audio Measurements.png


Jitter performance is excellent with almost no spurious tones:

Monoprice THX DAC and Balanced Headphone Amplifier USB Jitter Audio Measurements.png


Linearity is very good and just shy of excellence:
Monoprice THX DAC and Balanced Headphone Amplifier USB Linearity Audio Measurements.png


Multitone test shows extremely even performance across the board:
Monoprice THX DAC and Balanced Headphone Amplifier USB Multitone Audio Measurements.png


The high frequency dynamic range between test tones and top of the distortion spikes is about 105 dB which should do justice to any CD rate music for sure.

Intermodulation distortion versus input level shows the same higher noise level as indicated in the dashboard:
Monoprice THX DAC and Balanced Headphone Amplifier USB IMD Audio Measurements.png


We only get better performance than Topping DX3 Pro ($250) until we get to max level where noise becomes less material.

Here is the power versus distortion and noise using 300 ohm headphone load:
Monoprice THX DAC and Balanced Headphone Amplifier USB Power 300 Ohm Audio Measurements.png


I had to set the volume level to +6 dB to get it to produce the max volume/clip. Otherwise it would end a bit early in power level. Once again the Topping DX3 Pro in low gain has a noise advantage over Monoprice THX desktop. Power level though is excellent and a match for topping at 129 milliwatts (I like to see > 100 milliwatt).

There seems to be more current available to drive lower impedance loads such as 33 ohm:
Monoprice THX DAC and Balanced Headphone Amplifier USB Power 33 Ohm Audio Measurements.png


Now the Monoprice pulls ahead producing one watt of output using its 1/4 inch jack. At higher volumes it is also able to maintain lower distortion. This seems to be the benefit of inclusion of THX technology.

Output impedance for the 1/4 inch jack is an excellently low 1.3 ohm:

Headphone Amplifier Ouptut Impedance Measurements Review.png


So don't worry about it changing the frequency response of your headphones.

Analog (XLR) Input Audio Measurement
For historical reason, I am running high power headphone amps at 5.8 volts output using XLR input at 4 volts:
Monoprice THX DAC and Balanced Headphone Amplifier XLR Audio Measurements.png


As noted, this is quite a bit lower performance than Massdrop THX AAA 789. Distortion spike is now up to nearly -102 dB which is dominating the SINAD score.

Instead of one signal data point, we can see the THD+N versus power at different input levels:
Monoprice THX DAC and Balanced Headphone Amplifier XLR Power at 300 ohm Audio Measurements.png


We are not in the same class as Massdrop to be sure. Nothing is broken though and we have excellent amount of power. Noise is also slightly lower if you don't go above 0 dB.

Same picture emerges when we change the load to 33 ohm:
Monoprice THX DAC and Balanced Headphone Amplifier XLR Power at 33 ohm Audio Measurements.png


Balanced Headphone Output
Running a "fully balanced" chain from XLR input to XLR headphone output at 50 ohm we get:
Monoprice THX DAC and Balanced Headphone Amplifier XLR Power at 50 ohm Audio Measurements.png


Power nicely quadruples as I like to see. Noise level though rises so don't use it unless you need the extra power.

Examining the nature of the noise and distortion relative to power showed something odd:

Monoprice THX DAC and Balanced Headphone Amplifier XLR THD vs Frequency Audio Measurements.png


The rising distortion relative to noise is unfortunate but there is a sudden drop indicating that the frequency response is limited. I ran the test up to 40 kHz and got this:

Monoprice THX DAC and Balanced Headphone Amplifier XLR Frequency Response Audio Measurements.png


So a roll off is occuring. Are the analog inputs digitized? They seem to be given the perfect channel balance relative to volume knob:

Monoprice THX DAC and Balanced Headphone Amplifier XLR Channel Mismatch Audio Measurements.png


I ran the signal to noise ratio only in XLR analog input:
Monoprice THX DAC and Balanced Headphone Amplifier XLR SNR Audio Measurements.png


If the inputs are digitized then I should go back and run them again with USB. For now, we are falling short in both measurements with the 50 millivolt not being all that good:

Headphone Amplifier 50 millivolt SNR Table and Review.png


Headphone Listening Tests
The power versus distortion+noise are a power predictor of subjective performance and such was easily the case here. Using either my Sennheiser HD-650 and Hifiman HE-400i, I had thundering bass, detail, dynamic range and as much gain as I wanted. No issues at all subjectively using these headphones. And if you need more power, you can always have it using balanced output.

Conclusions
The Monoprice THX AAA Desktop DAC and headphone amplifier seems to have one issue: higher noise level. If it didn't have this issue, it would easily match the performance of our reference stand-alone headphone amplifiers (Massdrop THX AAA 789 and JDS Labs Atom). Performance otherwise is predictable and solid. There is ample power to drive anything you throw it and subjectively, delivers all that you would want in a desktop headphone amplifier and DAC. And importantly, one that you can buy now.

In this regard, I say it is a very good alternative to Topping DX3 Pro, albeit at double the price and with usability quirks (volume control) and lack of remote.

All in all I am happy to put the Monolith by Monoprice Desktop Balanced Headphone Amplifier and DAC with THX AAA Technology on my recommended list.

------------
As always, questions, comments, recommendations, etc. are welcome.

I noted in my last review that the pink panthers were threatening to go on strike, complaining about too many hours of work (lazy bastards). Well, they did go on strike. The one in the picture above is the only one that crossed the picket line. He is now getting death threats so I appreciate if you all donate money so that I can get him a body guard using:

Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
 
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#2
@amirm - from what I read, everything analog is fed through a ADC conversion.

From Andrew of THX: "Yes analog input is converted to digital by ADC, regardless of DIRAC on/off."

Thanks for taking a look at my unit. I forgot about the Volume wheel the other day when you asked what I didn't like about it. I do find it a bit quirky when you scroll really fast.
 

amirm

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#4
Your Pink Panther looks really calm. I'd be worry to dead if I was it :eek:
He has a condition where he is always staring into empty space. He is been to many doctors but apparently there is no cure.
 
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#6
is the noise mentioned in the audible band?
The unit tested was mine. I noticed audible noise floor hissing only when I used Campfire Audio (Orion, Andromeda, Solaris), BGVP DM6, and other super high sensitivity IEMs using a balanced connection (2.5mm to XLR). There was noticeable hiss on that. Otherwise, using every other headphone and less sensitive IEM I owned, noise floor was not an issue. For reference, I used it with Senn HD58X and 6XX, AKG M220, Focal Elex/Elegia, various Audeze headphones, and Hifiman HE560 without noise issues.
 

mi-fu

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#7
Thanks Amir for the review.

I was about to purchase this about 6 months ago when it was launched. I was debating between this Monoprice offer and THX 789. I eventually bought the 789 in its second drop - probably one of the best purchase I made.

Even apart from the firmware failure in the initial preview, this detailed measurement further demonstrates that good engineering is as important as, if not more important than, good components. If my memory is correct, I think Andrew Mason of THX mentioned that THX 789 was designed by them, but not this Monoprice one. It may explain parts of the story.

I think several weeks ago Monoprice had a $150 off $500 promotion. That would make this DAC / AMP combo at a very appealing price point nonetheless.
 

amirm

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#10
is the noise mentioned in the audible band?
The dashboard bandwidth is 22.4 kHz so generally yes. Note however that it may not be audible necessarily.
 

amirm

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#11
hey amir , the legends of the graph before the output impendence are mislabled it reads "massdrop"
THanks. I must have mistyped that 20 times. :) I caught and fixed them but I missed that one. Fortunately the larger text in the graph is correct.
 

amirm

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#12
The product is called Monolith.
They have a bunch of products called "Monolith." The only unique way to name is to quote the full sentence I did in the conclusion section. I can't believe how many words they put in the name of the product.
 
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#14
Thanks for the measurements, I purchased this last week when there was $125 off 500 deal and like to use it with HD650 and m1060. I was trying to justify the purchase that how I got to this thread.

For those who want to understand the measurements, here has kind of "layman" explanations on some of the terms: http://www.apexhifi.com/specs.html
 
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#15
This is disappointing!!!! I was hoping for a 789 with and integrated dac...that I could actually buy! Guess I'll keep my finger poised above the "Request" button on Massdrop waiting for it to turn into a "Buy" button.
 
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#16
I am looking to buy one of these but I am on the fence with the noise issue.

Would love to get my hands on a THX 789 (like everyone else) but that seems to be unlikely in the near future.

Will be only using the USB input for my Aeon flow's & HD800 S's will the noise be an issue with these headphones?
 

Sythrix

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#17
Excellent review. Think I'll skip this one, given the price and what I already have.
 

amirm

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#18
I am looking to buy one of these but I am on the fence with the noise issue.
It shouldn't be an audible issue. It is more of a measurement/engineering excellence thing.

I believe they have a satisfaction guarantee. It is a pain to return things to them but I think they will take it back if you complain about the noise.
 
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#19
It shouldn't be an audible issue. It is more of a measurement/engineering excellence thing.

I believe they have a satisfaction guarantee. It is a pain to return things to them but I think they will take it back if you complain about the noise.
Many thanks for the reply amirm, I think I will go for it as it seems a good product all in all.

Was looking to go for the Arcam rHead & SMSL SU-8 but I do like the all-in-one solution.

Would there be anything other than the THX 789 that compares for the price?
 

amirm

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#20
Would there be anything other than the THX 789 that compares for the price?
JDS Labs Atom if you don't need the extra power of balanced output. It is only $99 and availability is good.
 
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