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Review and Measurements of Massdrop THX AAA 789 Amp

Grave

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Oh, that actually existing similar Monoprice product would be interesting if it measured well.
 

maxxevv

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But how do you convert unbalanced into balanced?

RCA comes with 2-pins each.

3-pin XLR comes with 2 poles + Earth.

In the above connection, the Earth pin of the 3-pin XLR is ignored. So its just Left RCA + and Left RCA - to Left XLR + and Left XLR -, Left XLR earth is left unconnected. Likewise for the right RCA connection.

At least that's how I understand it works.

I'm fortunate that I didn't have to deal with that as my DAC comes with XLR outputs.
 

xineis

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RCA comes with 2-pins each.

3-pin XLR comes with 2 poles + Earth.

In the above connection, the Earth pin of the 3-pin XLR is ignored. So its just Left RCA + and Left RCA - to Left XLR + and Left XLR -, Left XLR earth is left unconnected. Likewise for the right RCA connection.

At least that's how I understand it works.

I'm fortunate that I didn't have to deal with that as my DAC comes with XLR outputs.

Well, I know how the connections work...

What I meant was: when you ignore the "earth", you just throw the benefit of having a balanced connection out of the window.
 

Nango

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What would the mechanism for a difference be?

I dont know, I just suppose it can't be the same, it is a difference of 100% that you apply into the membrane, diaphragma, or whatever it is what makes we hear the sound..... might control better the attenuation, the dynamics of the driver.
 
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maxxevv

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Well, I know how the connections work...

What I meant was: when you ignore the "earth", you just throw the benefit of having a balanced connection out of the window.

It depends on the system implementation I suppose. The main benefits of "balanced" are in the power delivery and reduction of signal cross talk over long cables.

I'm not sure how the "earth " pole/ pin will affect those areas as such an area of electrical engineering isn't something I have spent enough time on.
 

derp1n

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I dont know, I just suppose it can't be the same, it is a difference of 100% that you apply into the membrane, diaphragma, or whatever it is what makes we hear the sound.....
That is not at all how it works.
 
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amirm

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Assuming both of their performance would be similar in other aspects, do you still think the Massdrop one is a better choice over Monoprice 788, because of the higher max power?
I do because I never want the amplifier to be the limiting factor. I am saying this as someone who has speaker amplifiers that are rated at 500 watts into 8 ohms. :) People who listen at lower levels don't need to share my preferences here.
 

Jimster480

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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.
Can't believe I didn't see your response, thanks for testing it!
Since you find the back emf reducing the performance well.... Does that mean it would be extra bad with planar headphones?
Also since you suggest balanced inputs, should I output balanced from my DX7 even to use with single ended headphones?
 
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amirm

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Also since you suggest balanced inputs, should I output balanced from my DX7 even to use with single ended headphones?
Sure. All headphones are balanced since they are not referenced to ground no matter which way you drive them.
 
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amirm

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Since you find the back emf reducing the performance well.... Does that mean it would be extra bad with planar headphones?
Our hearing sensitivity is pretty poor in low frequencies so I am not sure we have identified any kind of audible problem. And at any rate, this seems to be an issue with every amp I have tested.
 
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Our hearing sensitivity is pretty poor in low frequencies so I am not sure we have identified any kind of audible problem. And at any rate, this seems to be an issue with every amp I have tested.

Have you considered testing an Benchmark Media ABH2 with real speakers or headphones as a load? There is a growing number of people who use it as a headphone amp and that amp seems to be pretty resilient to speaker loads? Would be interesting to see whether that still distorts at these very high levels.

Cheers

Thomas
 

Jimster480

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Our hearing sensitivity is pretty poor in low frequencies so I am not sure we have identified any kind of audible problem. And at any rate, this seems to be an issue with every amp I have tested.
Ah okay,
This is what I was thinking. But I wasn't sure if you were talking about specifically poor performance with this particular design over other designs.
Sure. All headphones are balanced since they are not referenced to ground no matter which way you drive them.
So if I use Single Ended input and output then it doesn't matter vs balanced input single ended output?
Sorry, I am just trying to clarify if it will benefit me or not (with DX7 as a source) since I don't currently own ANY balanced cables at all.
 
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amirm

amirm

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Have you considered testing an Benchmark Media ABH2 with real speakers or headphones as a load? There is a growing number of people who use it as a headphone amp and that amp seems to be pretty resilient to speaker loads? Would be interesting to see whether that still distorts at these very high levels.

Cheers

Thomas
Hi Thomas. I did not know people were using ABH2 for headphones. For now, I have an offer for their HPA4 from them. Let me test that first in the same manner and then I will see if I have any chips left with Benchmark to borrow more of their stuff. :)
 
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amirm

amirm

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So if I use Single Ended input and output then it doesn't matter vs balanced input single ended output?
Sorry, I am just trying to clarify if it will benefit me or not (with DX7 as a source) since I don't currently own ANY balanced cables at all.
No it does matter. The decision to use balanced on the input has nothing to do with balanced on the output/headphone side.

Benefit of using balanced on the input is that mains leakage is essentially eliminated. So you should deploy it regardless of how you connect your headphones.

On the headphone side, if balanced output has more power and you need that extra power, you should use that too. Again, this has nothing to do with how you drive the headphone amplifier. If you don't need the extra power, then use unbalanced headphone but still drive the unit with balanced interconnects.
 

Jimster480

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No it does matter. The decision to use balanced on the input has nothing to do with balanced on the output/headphone side.

Benefit of using balanced on the input is that mains leakage is essentially eliminated. So you should deploy it regardless of how you connect your headphones.

On the headphone side, if balanced output has more power and you need that extra power, you should use that too. Again, this has nothing to do with how you drive the headphone amplifier. If you don't need the extra power, then use unbalanced headphone but still drive the unit with balanced interconnects.

Thanks for clearing this up.
I will order some balanced interconnect cables.

On another note, do you think its possible for you to do a quick test with the DX7 with your new analyzer? I'm just interested to see if the SINAD of the original DX7 passes that of the DX7s considering it has no "midrange hump".
The original test of the DX7s suggested that the DX7 original is actually superior in some ways, but it hasn't been retested.

Once again I'm thankful for your work here to prove or disprove if the hype was justified! Now I just have to decide what to do with this amp as far as placement/usage since its too large to actually sit on top of the DX7 (which is how I have it now).
 
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Hi Thomas. I did not know people were using ABH2 for headphones. For now, I have an offer for their HPA4 from them. Let me test that first in the same manner and then I will see if I have any chips left with Benchmark to borrow more of their stuff. :)

HPA4 sounds like a great target too!

The question on my mind is how much of this distortion at the measurement point is actually interfering with control of the membrane by the amp? Are there amps that are more susceptible to this than others. Do we understand why?

Cheers

Thomas
 

Headphonaholic

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Wow! This a game changer indeed! Really hate myself for not getting one of these... I guess I'll be selling some gear in the near future lol. I'm gonna hold off to see how the Monoprice THX amp/dac does before picking one up. If it performs as well as this amp with a good dac, it maybe the device to get.

Thank you Amir for reviewing this and thank you to the person (@Sythrix?) that drop shipped it to Amir!
 

rajapruk

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We know that THX was very very much involved in the total technical design of the Massdrop amp. That is the critical success factor here, I think.
I wonder if the Monoprice amp has the same kind of involvement from THX? I read somewhere that Andrew Mason of THX wrote that Monoprice choosed the DAC-chip themselves. That maybe indicates a little less THX-involvement overall.
 
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Veri

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We know that THX was very very much involved in the total technical design of the Massdrop amp. That is the critical success factor here, I think.
I wonder if the Monoprice amp has the same kind of involvement from THX? I read somewhere that Andrew Mason of THX wrote that Monoprice choosed the DAC-chip themselves. That maybe indicates a little less THX-involvement overall.
But isn't that same Andrew answering questions on the monoprice Question/answer product page of the amp?

Screenshot at Oct 29 16-27-45.png
 
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