Review and Measurements of Massdrop THX AAA 789 Amp

[Veri]

Is this really some audible problem? I mentioned making a balanced cable from my portable Dac (Opus 1s, its has such type of connection mentioned in the manual, in fact) — to Amp connection at some other forum and got laughed at by many members, they say it's a marketing thing and I should not bother...

The thing is that balanced makes so much sense over long lengths, for example microphone XLR cables. MUCH less noise over those lines, unbalanced could have serious hum.

In our home set-ups, a cable run of 1-1.5m has much less chance of getting into any serious noise problems. Multiple RCA runs from multiple devices might end up with a ground loop somewhere, in which case balanced XLR can again have important benefit in such a run, but in simple use cases RCA is perfectly fine in which case one could indeed say it's a marketing thing.
From a theoretical standpoint no matter the length of cable run, balanced will be better though, but from a practical and budget standpoint there is less sense in going for the pricier balanced gear.

Andrew of the THX team said a simple RCA>XLR cable into a fully differential amp can already have some good noise reduction so fully balanced might not even be necessary with the right gear. Not all amps will accept unbalanced over XLR though! Also, some people will simply like the XLR connector that much more than the stiffer RCA/BNC connector ...

 

[pkane]

The thing is that balanced makes so much sense over long lengths, for example microphone XLR cables. MUCH less noise over those lines, unbalanced could have serious hum.

In our home set-ups, a cable run of 1-1.5m has much less chance of getting into any serious noise problems. Multiple RCA runs from multiple devices might end up with a ground loop somewhere, in which case balanced XLR can again have important benefit in such a run, but in simple use cases RCA is perfectly fine in which case one could indeed say it's a marketing thing.
From a theoretical standpoint no matter the length of cable run, balanced will be better though, but from a practical and budget standpoint there is less sense in going for the pricier balanced gear.

Andrew of the THX team said a simple RCA>XLR cable into a fully differential amp can already have some good noise reduction so fully balanced might not even be necessary with the right gear. Not all amps will accept unbalanced over XLR though! Also, some people will simply like the XLR connector that much more than the stiffer RCA/BNC connector ...

RCA is also a poorly designed connector. Making the hot (middle) connection before outer (ground) is usually not a good thing to do, especially when connecting to a powered amp. That's why pro components use XLR.

 

[ReAlien]

I was asking because in the manual to my portable DAC Opus 1s there is the following version of connection, see attached. I wonder if it is worth a bother of making a custom cable for this, will there be an actual audible result with THX AAA 789 and HE400i combo?

 

[AndrewMason]

@AndrewMason

Does the op-amp balanced configuration (otherwise known as BAL -> SE -> BAL) introduce common mode ground noise along this chain?

Hi Roen. No, you're safe. We used a fully differential architecture and payed a lot of attention to layout to prevent introduction of ground noise in the chassis.

 

[amirm]

Is this really some audible problem? I mentioned making a balanced cable from my portable Dac (Opus 1s, its has such type of connection mentioned in the manual, in fact) — to Amp connection at some other forum and got laughed at by many members, they say it's a marketing thing and I should not bother...

It is not a problem until it is. Vast majority of users have no audible ground loops with unbalanced. But one you do, remedies are hard to find.

 

[Roen]

Hi Roen. No, you're safe. We used a fully differential architecture and payed a lot of attention to layout to prevent introduction of ground noise in the chassis.

How is it fully differential if the signal becomes unbalanced along the chain?

 

[AndrewMason]

How is it fully differential if the signal becomes unbalanced along the chain?

How is it fully differential if the signal becomes unbalanced along the chain?

Differential and balanced aren't the same thing.

Balanced audio implies two equal and opposite signals used throughout.

Differential means every stage has an unpolluted view of the source signal with respect to source ground, and is able to reproduce the signal with respect to a clean view of the downstream device reference ground. This avoids pollution by any ground currents.

Proper differential is all that's required to maintain signal integrity. So long as the designer knows what they're doing, balanced isn't required.

 

[derp1n]

Balanced audio implies two equal and opposite signals used throughout.

Differential means every stage has an unpolluted view of the source signal with respect to source ground, and is able to reproduce the signal with respect to a clean view of the downstream device reference ground. This avoids pollution by any ground currents.

Interesting definition.

 

[ReAlien]

It is not a problem until it is. Vast majority of users have no audible ground loops with unbalanced. But one you do, remedies are hard to find.

Aha, that means that if there will be a problem, I will hear a hum or noise in headphones, and only in this case, I should go for a balanced connection to remedy that. It is not some distortion that would make music sound different, it's just an added noise issue. Am I correct?

 

[amirm]

Aha, that means that if there will be a problem, I will hear a hum or noise in headphones, and only in this case, I should go for a balanced connection to remedy that. It is not some distortion that would make music sound different, it's just an added noise issue. Am I correct?

Correct.

 

[Music1969]

Hi all, I just wanted to give an update regarding the crosstalk at the lowest gain. It occurred to me, since I had to put the volume control at 4 o'clock in the test that had the crosstalk issue, perhaps it's the potentiometer that's causing it. So I did another test, this time with gain setting "2", with 20 dBu input and the volume set to 1-2 o'clock to reach 6 dBV output, and I get a similar, albeit lower, increase in crosstalk!

So it looks like the increase in crosstalk is caused by the potentiometer (and varies with the position of the potentiometer), and not the gain setting.

View attachment 18352

Hi Andrew @AndrewMason

Does this plot like ok to you and nothing to worry about?

Or something may be wrong with his unit?

 

[pos]

@AndrewMason, when your design is used with an unbalanced source, is there any advantage or drawback in using a "pseudo differential" cable to the XLR input (RCA to XLR with balanced cable and ground/negative shorted on the RCA side) compared to connecting to the RCA input?

 

[Roen]

@AndrewMason, when your design is used with an unbalanced source, is there any advantage or drawback in using a "pseudo differential" cable to the XLR input (RCA to XLR with balanced cable and ground/negative shorted on the RCA side) compared to connecting to the RCA input?

Here's @AndrewMason 's response:

https://www.head-fi.org/threads/massdrop-x-thx-aaa™-789-linear-amplifier-impressions-thread.873576/page-25#post-14621510

TLDR; Don't short at the XLR pin side, run two separate wires and connect them to the RCA shield.

 

[AndrewMason]

Hi Andrew @AndrewMason

Does this plot like ok to you and nothing to worry about?

Or something may be wrong with his unit?

All good. SE Crosstalk < -100 dB @ 1 kHz is pretty low.

 

[GGroch]

The always subjective an usually entertaining Zeos just reviewed the thx-aaa-789 calling it a "game-changer'. No link as patreon only...should be up in the next 24 hours I think.

The Following is a general question about Balanced Amp Performance...please let me know where to put it if it is in the wrong thread.

My Question... Zeos and Others have subjectively noticed huge differences in the balanced vs unbalanced performance of this and other DAC/AMPS..... Balanced being noticeably superior. Should this be so? I understand balanced is designed for reducing noise interference...lacking noise, no benefit. BUT, fully balanced amps (and perhaps DACS) have twice as much stuff inside to reproduce both halves of the signal. As a result they also usually produce significantly more power. On the other hand, some highly regarded mfg like Benchmark do not offer HP Amps with fully balanced circuitry because they say it can perform worse. (They do offer XLR connections on HPA because of its superior conductivity). Are balanced amps...outside of noise superior? One source says they HAVE to provide twice the power to reach the same volume because they are reproducing the entire signal...not half.

 

[derp1n]

Just completely ignore Zeos when it comes to anything vaguely technical, the guy is clueless and given how long he's been doing this (and has had time to learn), wants to stay that way.

 

[GGroch]

Right... my comment is on his Subjective listening impressions...nothing technical. And he is not alone in subjectively noticing major improvements in balanced mode in amps. Most also note amps are louder on balanced...whether that is due to gain differences or actual power I do not know.

 

[Veri]

The always subjective an usually entertaining Zeos just reviewed the thx-aaa-789 calling it a "game-changer'. No link as patreon only...should be up in the next 24 hours I think.

He's not publicising it for now lol https://www.massdrop.com/buy/massdrop-x-thx-aaa-789-linear-amplifier/talk/2280868

I finished the review of this and gave it to my patrons yesterday. I will not be releasing the review until this comes back in stock because 10,000 people foaming at the mouth for X weeks is not a pretty picture. #lifealteringamptech

About balanced, many amps have different topologies for SE and balanced. Not the THX AAA. The measurement by amir prove NO difference besides power. If zeos thinks balanced sounds better on this particular amp, he's loony. Or well, he's wrong at the very least

 

[derp1n]

Right... my comment is on his Subjective listening impressions...nothing technical. And he is not alone in subjectively noticing major improvements in balanced mode in amps. Most also note amps are louder on balanced...whether that is due to gain differences or actual power I do not know.

Differential generally has twice the voltage swing, so effectively has 6dB more gain. Depends on the design, though.

It's theoretically possible to design an amp where either the single-ended or balanced/differential output sounds different from the other. But there's no inherent difference, it's down to design. In general, when you see people claiming balanced sounds better you can simply assume they are suffering from bias and/or failed to volume match.

 

[GGroch]

Ah yes. As an old sometimes devious stereo salesman I can confirm failed volume match works every time