Review and Measurements of Massdrop THX AAA 789 Amp

[Headphonaholic]

Just made a preorder of Monoprice AK/THX dac-amp https://www.monoprice.com/product?c_id=120&cp_id=12008&cs_id=1200801&p_id=24459&seq=1&format=2&res=1
Hope that they will deliver to Finland, Europe.... Amazon.de is another supplier of Monoprice products, but this gadget is not on the list.
This will replace my Audio-GD NFB-12 with dual Wolfsons.

How did you preorder it? I've never seen a preorder option on any of monoprices products.

 

[Veri]

How did you preorder it? I've never seen a preorder option on any of monoprices products.

I think he means just to be 'alerted' for release. That seems like the only option?

 

[Juhazi]

^Yep alert and on the wishlist. They obviously don't take official preorders. There will be heavy traffic on their server when a batch arrives!

 

[Jimmy]

For european folks buying from USA or other non EU countries is a lottery, between shipping cost, customs and VAT something that costs 400 USD can well get over 600 EUR, the Massdrop amp, leaving QC issues aside is a good value at its current price, but when buying from outside USA the added cost puts it another price segment, same for the monoprice.

Amazon sells in europe some monoprice stuff at reasonable prices but they are mostly cables, 3D printers and a few headphones, but none of the monolith amps.

 

[amjosh]

This is a review and detailed measurements of the just Massdrop THX AAA 789 headphone amplifier. It was drop shipped by request of a kind member for testing. It retails for USD $349.99. The unit had a log gestation period with customers having to wait months to receive the first allotment. The second drop had a ship date of February so if you have not gotten in line, you will be waiting a long time for one. Is the wait worth it? Let's find out.

On the industrial design, Massdrop is using their current design language for their larger desktop audio products which in my opinion is a good thing. While the unit does not have a luxury feel to it, it looks serious and not cheap:

View attachment 16938​

Very conveniently, there are three headphone jacks in front: 4-pin XLR for balanced headphones, and both 3.5 mm and 1/4 inch for single ended. As usual, please note that the word "balanced" here simply means more potential power, and has nothing to do with balanced interconnects between audio gear.

Nicely again, we have three gain settings and not he usual two.

On the backside, we have both unbalanced input (and pass through) and balanced. For my measurements, I tested with the balanced input. For listening tests, I used the unbalanced RCA.

The heart of this unit as the name indicates, is a special amplifier from THX with distortion correction logic that is supposed to yield unbelievably low distortion. Let's get into that as I am sure that is the main thing you all are interested in.

Measurements
For consistency with my last couple of headphone amplifier reviews, I set the output at about 5.7 volts:

View attachment 16939

Wow! That is stunning. We are getting SINAD (signal above distortion and noise) of 117 dB. That beats the best DAC we have ever measured (115 dB SINAD). It by far shatters all previous records.

THX/Massdrop advertise much lower numbers though. If you look at the distortion products, they are around -130 dB and that is the number advertised (more or less). Our SINAD is much lower because of noise. The FFT transform artificially lowers the noise allowing us to see those distortion spikes. We can confirm that by measuring signal to noise ratio:
View attachment 16940

The dashboard uses a 600 ohm load. So let's test it with a more realistic 300 Ohm load and see how much power we get:

View attachment 16941

We get 150 milliwatts of power at distortion of 0.0002% or essentially our dashboard SINAD number (right axis). The graph is essentially noise limited until we hit the saturation point.

Let's go to the other extreme at 33 ohm:
View attachment 16942

As expected we get a ton more power at 1.3 watts. Performance remains impeccable with both channels exactly on top of each other producing astonishingly small distortion and noise at that power level. Quite remarkable.

For balanced, I have a single fixture at 50 ohm so let's see how much power we get there relative to unbalanced:

View attachment 16943

There is no penalty in noise and distortion for using balanced. You simply get copious more power at whopping level of 3.5 watts before clipping.

Output impedance is 1.0 ohm which I would normally say is very good but given the above performance, I wish it was half an ohm lower:
View attachment 16944

EDIT: my measurements always show higher than minimum that can be measured. See this post for the best case impedance which is close to zero: https://www.audiosciencereview.com/...-of-massdrop-thx-aaa-789-amp.5001/post-112221


Frequency response is essentially ruler flat to 40 kHz:
View attachment 16945

Last but not least, let's look at channel imbalance as we manually vary the volume from max to min:
View attachment 16946

Not as good as digitally controlled volume controls but very good nevertheless with just 0.2 dB of error right before muting.

Listening Test
For the source, I hooked up my Khadas Tone Board DAC to the unbalanced input of the Massdrop THX AAA 789. And as always started listening with my Sennheiser HD-650. This combination provided incredible level of transparency. I could set the volume level high and hear the slightest amount of background noise in recordings! It was so good that variations in fidelity of the source was more apparent than I had ever experienced.

With loud electronic music, I could easily set the cups to motion on the HD-650 whit no hint of distortion. Power was ample and clean.

With "audiophile" recordings with a lot of headroom, I had plenty of power but not ear piercing. So would be nice to test the balanced output with that. Alas, this unit arrived too soon for me to build the balanced cable for my Sennheisers. I will finish that project and report back. For now, it is really not necessary to have balanced given the clean power you get single ended out of this unit.

I then switched to Hifiman HE-400i. Same experience continued with effortless power pushing the transducer to point of rattling/distortion. It is an interesting sensation akin to having subwoofers in your ears! Of course not recommended for any length of listening.

I plugged in my low impedance IEMs to see if I could detect any hiss but I could not.

Conclusions
It takes a lot for someone like me who likes finding faults to smile ear to ear in testing audio gear. But that is exactly what THX and Massdrop have achieved. With a SIAND that matches the best dynamic range of our hearing system, you are assured that the only distortion you hear is either in the source or your headphones. Not only that, but we also have tons of power to drive any headphone at a price that is hard to believe for this level of performance.

So let me make this short: the Massdrop THX AAA 789 has my strongest recommendation. Buy one and be happy forever.

-----
As always, any questions, concerns, comments, corrections, etc. are welcome.

If you like this review, please consider donating 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). It will enable me to pay for gear that is not offered for loan.

I did buy it and boy am I a happy listener. I feel a kind of empty now, my quest to find the perfect amp just ended

 

[maxxevv]

I did buy it and boy am I a happy listener. I feel a kind of empty now, my quest to find the perfect amp just ended

Onwards to the search for the perfect DAC and perfect headphones .......

 

[Rod]

For european folks buying from USA or other non EU countries is a lottery, between shipping cost, customs and VAT something that costs 400 USD can well get over 600 EUR, the Massdrop amp, leaving QC issues aside is a good value at its current price, but when buying from outside USA the added cost puts it another price segment, same for the monoprice.

Amazon sells in europe some monoprice stuff at reasonable prices but they are mostly cables, 3D printers and a few headphones, but none of the monolith amps.

I did buy it and boy am I a happy listener. I feel a kind of empty now, my quest to find the perfect amp just ended

Now you need to find the perfect headphones to go with it? Dac? Headphone stands? Wire? RBG lighting? Just trying to help fill in that empty feeling and empty that wallet.

 

[maxxevv]

Now you need to find the perfect headphones to go with it? Dac? Headphone stands? Wire? RBG lighting? Just trying to help fill in that empty feeling and empty that wallet.

lol .....

 

[Grave]

RGB

 

[maxxevv]

RGB

Something like this perhaps ??

https://www.aliexpress.com/item/Wat...lgo_pvid=97d77aea-f346-44b3-b520-1b49250804ac

 

[Grave]

Corsair does an RGB headphone stand.

https://www.amazon.com/Corsair-Gaming-Premium-Headset-Surround/dp/B074ZQJW9R

 

[Rod]

Corsair does an RGB headphone stand.

https://www.amazon.com/Corsair-Gaming-Premium-Headset-Surround/dp/B074ZQJW9R

That lighting is the same kind thats on my mouse.
https://www.amazon.com/gp/product/B07B7F3NLC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

[amjosh]

Now you need to find the perfect headphones to go with it? Dac? Headphone stands? Wire? RBG lighting? Just trying to help fill in that empty feeling and empty that wallet.

Headphones is definitely the one. Currently I am kind of maxed out at $600 range with Hifiman HE560 and Audeze EL8. Want to buy the perfect closed back headphones. Any recommendations??

 

[Rod]

Headphones is definitely the one. Currently I am kind of maxed out at $600 range with Hifiman HE560 and Audeze EL8. Want to buy the perfect closed back headphones. Any recommendations??

So many headphones and I am in rural America. Most of the headphones people talk about here I have never even seen. The ones I have I just went on reviews and recommendations from those who have them. Saying that, I am enjoying the open backed balanced HD 6xx with the THXAAA amp right now.

 

[Rod]

Groovin to this:

 

[tomchr]

Analog ICs are usually built on very obsolete semiconductor lines. So no hope of 14nm anything.

I spent a decade of my life designing analog ICs for National Semiconductor (and Texas Instruments after TI bought National) before setting out on my own. The first analog process I worked with was still under development when I hired on in 2005. I believe National released it in 2005 or 2006. It was a silicon-on-insulator (SOI) process that featured high-end NPNs and PNPs (very unusual for semiconductor processes these days), as well as two types of CMOS. It also featured a thin film resistor module with exceptionally tight matching. You can read more about it here: http://newscenter.ti.com/news-releases?item=124579. It was (still is!) a state-of-the-art process and certainly not obsolete by any means.

That said, you're not likely to find any analog products made on a 14 nm process any time soon. First off, the 1/f noise of such processes is horrendous, so the first thing the designer would do is to make the MOS devices larger. I don't recall designing anything using devices with gate lengths smaller than 1.0 um (1000 nm) for anything other than logic gates for this reason. The other reason is that the cost of the poly-silicon mask (used for MOSFET gates) is absolutely insane for the fine featured processes. So if you don't use the small devices, there's no point in using a tiny feature process.

While the analog-optimized processes may not feature the sub-100 nm gate lengths of a state-of-the-art CMOS process, they're by no means "obsolete" or "outdated".

Sorry for barging in like that, but I found the distinction important to make.

Now back to the topic of the thread: I'm puzzled that the THX789 "only" provides 3 W into 33 Ω. The specs say 6 W. What gives? Are they playing the "two channels of three watt each -> 6 W" game? Nice amp, though. Getting distortion numbers that low is no easy task.

Tom

 

[Juhazi]

If export to Europe gets difficult, I must ask my wife's sister in Pacifica, CA to buy it and bring it to me later on. I couldn't find anything like it in EU, except Benchmark.

Sent Monoprice a question about delivery to Finland, EU.

 

[pos]

Hi Tom, nice to read you here!

Now back to the topic of the thread: I'm puzzled that the THX789 "only" provides 3 W into 33 Ω. The specs say 6 W. What gives? Are they playing the "two channels of three watt each -> 6 W" game?

Here are Amir measurements on the balanced output:

50 ohms load : 3.5W, 13.2V, 0.26A (voltage limit reached)
(and close to 4W at 1% THD)

24 ohms load: 5.6W, 11.6V, 0.48A (current protection reached)

16.7 ohms load : 5.6W, 9.7V, 0.58A (current protection reached)

 

[rajapruk]

So 32ohm load would also give 5,6W balanced output, you think?

 

[rajapruk]

@tomchr It would be nice if you could send some amp of yours to Amir for test. It would be good marketing for you, I guess.