Review and Measurements of Massdrop THX AAA 789 Amp

[Veri]

Hi @amirm

What's the reason you didn't test distortion with real headphone loads with the THX 789, like you previously did with Chord Hugo2's headphone output?

Same with the JDS Lab Atom headphone amp measurements too.

Is there something faulty with the Hugo2 test you did?

For one thing you can see it was done with previous analyser set-up. Furthermore I'm sure that testing different headphones in such a test can be time-consuming. Amir now has several dummy loads which should approximate different headphones.

 

[amirm]

Hi @amirm

What's the reason you didn't test distortion with real headphone loads with the THX 789, like you previously did with Chord Hugo2's headphone output?

Same with the JDS Lab Atom headphone amp measurements too.

Is there something faulty with the Hugo2 test you did?

Hi there. The original interest in that test came from an article from Benchmark and implied their performance doesn't degrade with headphones but others do as shown. Well, we eventually tested the Benchmark and it too showed the same issue. After that, the interest in the test died down.

I can run it just as well with my new analyzer. It is just that it is hard on headphones and annoys others in the house. Also, the effect is dependent on noise in the room, the fit of the headphone on the measurement rig, etc.

 

[Schackmannen]

Hi there. The original interest in that test came from an article from Benchmark and implied their performance doesn't degrade with headphones but others do as shown. Well, we eventually tested the Benchmark and it too showed the same issue. After that, the interest in the test died down.

I can run it just as well with my new analyzer. It is just that it is hard on headphones and annoys others in the house. Also, the effect is dependent on noise in the room, the fit of the headphone on the measurement rig, etc.

I forget who asked to see a real headphone load versus dummy load so here it is:

View attachment 16962

As with my previous tests of Benchmark DAC3 and ADI-2 Pro, there is significant degradation in low frequencies due to reverse EMF current from the headphone driver getting strong.

Note that the above is at low output level (1 volt) and with double the bandwidth of the dashboard. As such, THD+N is much lower even with the dummy load (33 ohm).

On the plus side, the ruler flat response is impressive with dummy load. There is no frequency dependent components.

You did test it quite a while ago

 

[Schackmannen]

And this was Andrew Mason's thoughts about that test:

And regarding the Grado and other headphone non-linearities due to EMF, I'm guessing it's mostly the headphones cable impedance that permits the non-linear EMF to create this distortion. A Kelvin connection inside the 1/4" plug would help you separate the variables. This is a good example of why cable impedance should ideally be much lower than driver impedance.

 

[Music1969]

Well, we eventually tested the Benchmark and it too showed the same issue. After that, the interest in the test died down.

Thanks @amirm , I missed these results.

So Chord Hugo2, Benchmark DAC3 and RME ADI-2 DAC and THX 789 all suffered a similar fate with low frequency distortion with dynamic driver loads.

I’m late to the party but I find it rather interesting.

 

[Music1969]

And this was Andrew Mason's thoughts about that test:

The Focal Utopia stock headphone cable has an impedance less than 1 ohm (less than 90 milli Ohm), much much less than the driver impedance.

But still Chord Hugo2 (output impedance less than 1 ohm) measured bad in low frequency distortion, with Focal Utopia as the load.

Similar looking distortion the RME ADI-2 and Benchmark DAC3 and THX 789 show with the dummy load.

 

[MC_RME]

No one has ever shown that the EMF that one can measure when the amps output is not exactly 0 Ohm (which is impossible to achieve, everything in the signal path has milliohms, and these are enough to cause irritating, measureable signals, thanks to the logarithm in those) has any relationship to distortion measured as acoustical output from the phones. One possible reason is that the phones distort much (a lot) higher than the EMF signal seems to imply. The 'damping' that the phones output stage could perform to the phones driver is IMHO also highly overrated, and in this specific case often ruined by the phones' cable resistance.

IMHO this is a non-issue that is not worth thinking about.

 

[JohnYang1997]

No one has ever shown that the EMF that one can measure when the amps output is not exactly 0 Ohm (which is impossible to achieve, everything in the signal path has milliohms, and these are enough to cause irritating, measureable signals, thanks to the logarithm in those) has any relationship to distortion measured as acoustical output from the phones. One possible reason is that the phones distort much (a lot) higher than the EMF signal seems to imply. The 'damping' that the phones output stage could perform to the phones driver is IMHO also highly overrated, and in this specific case often ruined by the phones' cable resistance.

IMHO this is a non-issue that is not worth thinking about.

I agree until the last sentence. It is often ruined by cable impedance. I did test at both amp output and at the driverm The measured distortion is 10 fold after wire at bass frequency. Though it may not be comparable to the headphones' own distortion. It's something to worry about. I also did test with output resistor. Lower the output resistor lower the distortion measured. It still makes difference even under 0.33ohm. Only under 0.05ohm there is absolutely no difference anymore. It proves that it is worth thinking about.
I also did a test with a 8 ohm iem. The distortion measured at headphones output is 0.002% on jds atom and dx3pro phone out. But on my own amp it's at 0.0002%, almost the same as resistor. So it actually matters in performance regardless of both atom and dx3pro has very low output impedance. The amount of feedback to be able to force the output to be the correct value is a lot.

All above are with the prerequisite/condition of measured performance still matters under the general believed audible threshold. And it's from pure performance standpoint.

 

[JohnYang1997]

So what I meant was. There are things that can be done to improve this. Both in the amplifier and the cable. If we can improve in these two regards we will achieve higher performance in the signal chain. Whether higher performance is needed that up to you.

 

[JohnYang1997]

In another word, when we take measurements with resistor this seriously but it has not as good performance with real headphones. Do we need to rethink the performance itself? Is there any reason to not take the worse looking real headphone load measurements over resistor load? Let's say
three amplifiers:
1 resistor load 0.00003% real headphone load 0.002%
2 resistor load 0.00006% real headphone load 0.0002%
3 resistor load 0.001% real headphone load 0.001%
This can certainly happen.

 

[escalibur]

Any Atom owners here? I'm curious about the unbalanced sound differences between Atom and 789.

 

[Veri]

Any Atom owners here? I'm curious about the unbalanced sound differences between Atom and 789.

I couldn't hear a difference between DX3 unbalanced output and DX3 line-out to THX AAA, unbalanced output.
I'd be surprised if the Atom would be any different in this regard.

 

[escalibur]

I couldn't hear a difference between DX3 unbalanced output and DX3 line-out to THX AAA, unbalanced output.
I'd be surprised if the Atom would be any different in this regard.

Thanks for the input.

Has anyone else compared 789 to Atom or even DX3 Pro?

 

[amirm]

Thanks for the input.

Has anyone else compared 789 to Atom or even DX3 Pro?

I of course have all three. The first two can play louder if you have that need. They also have better quality reputation than DX3 Pro. My daily driver remains the DX3 Pro because of integrated DAC, perfect volume control and nice display. I only take out the other two for testing.

 

[escalibur]

I of course have all three. The first two can play louder if you have that need. They also have better quality reputation than DX3 Pro. My daily driver remains the DX3 Pro because of integrated DAC, perfect volume control and nice display. I only take out the other two for testing.

Thanks for the info. Any comments on the sound differences?

 

[escalibur]

Live again!

https://drop.com/buy/drop-thx-aaa-789-linear-amplifierH

 

[graz_lag]

'Note: Due to the popularity of this product, we’re having trouble keeping it in stock. Preorder now and we’ll reserve your spot in our next run, expected to ship November 15th.'
A super-nice Xmas's gift !

 

[Silou]

Did they raise the price? It would cost me 500$ to get the 789 to Germany. I am very curious but I guess there is absolutely no need to upgrade. My Atom can drive anything I own in Low Gain. I think I need a new headphone to justify it

 

[PorchSong]

I'm not digging the "DROP + THX AAA 789" stretch logo. I like the simple clean logo of the original. I hope the one I ordered back two rounds ago has the old logo.

 

[Azeia]

My Atom can drive anything I own in Low Gain. I think I need a new headphone to justify it

Actually, the Atom has more power than the 789 if you're using the 789's unbalanced SE headphone output. I was confused about this myself, which is initially why I made an account to ask about it here and confirm. So even buying hard to drive headphones wouldn't really justify upgrading to the 789, unless you also had a balanced cable for them.