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:
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!
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.
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As always, any questions, concerns, comments, corrections, etc. are welcome.
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Review and Measurements of Massdrop THX AAA 789 Amp
- Thread starter amirm
- Start date
What would we consider a worthy DAC pairing with this thing?
I just went for Massdrop's SDAC. At that price point, I felt I could not really go wrong, especially given the high reviews. I do however have a couple other DACs lying around -- the AQ Dragonfly Red, and an older NuForce. I'll trial them out after I receive the AMP.
Take your pick from the SINAD thread.
aleksander
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Difference really audible?
Yes, I clearly heard him say different words for each of the amps he was talking about. Yes, I snark.
He did not bother with an ABX. He seems like a nice guy, but he just gave some opinions. The THX is much less costly than the NFB-1 and Jotunheim, and measures a ton better than both, so I know which way I'd go.
Kyle / MrHeeHo
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From what I understand Sennheiser has changed the tuning of their 600/650 series headphones over the years, or at the very least changed build materials. I'll go search and edit in a link if I can find what I'm trying to recallI'm am glad to read this as I was starting to doubt my pair of hd6xx.
I had a pair of 650s for many years, being replaced about 3 years ago by a pair of Oppo PM1s. First cans I found that I thought improved over the 650s.
I recently bought a pair of hd6xx as an alternative to test out my amp design and I was a little disappointed by the sound. It just wasn't how I remember the 650s. They just didn't have the naturalness I remember in the high frequencies. To the point where I was wondering if the 6xx really is the same as the 650.
Your comments just lead me to think it's just my rubbish audio memory
Edit: It was Tyll's review I was remembering but he didn't try to measure if there were any meaningful differences. https://www.innerfidelity.com/content/very-important-sennheiser-hd-580-hd-600-and-hd-650-page-2
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I believe the rca outs are just a pass through and aren't controllable
Getting a DX3 Pro for now and going to see if it runs the 6XX properly enough, if it doesn't the DX3 will serve as my DAC and I'll get the THX next time it drops
About 600 units in 2 days!
ReAlien
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@amirm I looked through the thread and couldn't find the comparison of gain modes (except for crosstalk), could you kindly show us how different gain modes fare in THX? I've read your article that generally advises using the lowest gain possible, yet it says that it depends on a particular amp. Crosstalk chart demonstrates that THX's Gain 3 is better, is it for the rest of the specs or just in crosstalk that Gain 3 is better?
OP
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- #719
I am not home but will put it on my todo list.
ReAlien
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I am not home but will put it on my todo list.
You are the best! Have a great weekend!)
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