• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Review and Measurements of Massdrop THX AAA 789 Amp

esm

Active Member
Forum Donor
Joined
Apr 9, 2018
Messages
182
Likes
327
Location
Berkeley, CA USA
That would require a fair bit more dismantling of my desk setup than I'm prepared to do right now; I might be able to revisit it later this week though (and at some point in the next month or two, I'll be sending it to Amir for testing anyway).

Purely subjectively, I've noticed no distortion from the introduction of the switch over the direct connection I briefly used previously, but obviously you shouldn't take that as anything other than some random person's perception, and given the track record of stuff I've sent to Amir, I'm sure it'll test horribly. ;) Also, keep in mind that this is a passive switch; I'd actually expect it to attenuate the signal a bit and lower the noise floor, rather than raise it, but this is consumer electronics: nothing is ever as you expect it.

FWIW, the SE846s have been the worst headphones I've ever owned as far as equipment matching goes (most sources and amps I connect them have a high enough noise floor to irritate me), and the fact that I was able to use the 789 without any tinkering made my day. And to my own ears, the balanced connection at reasonable volumes was fine, although again, you wind up with a pretty narrow range on the amp without lowering the source gain a bit.
 

AndrewMason

Member
Technical Expert
Joined
Oct 29, 2018
Messages
46
Likes
147
strangely, in the manual of focal clear headphones, it also says using a balanced headphone cable will produce better sound quality. i wonder if it is just marketing BS.


View attachment 18495
I suspect the biggest benefit of "balanced hp cables" is the elimination of crosstalk from shared ground return inherent in conventional 3-wire hp cables and shared ground contact resistance in TRS jacks. These are both measurable phenomena.
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
I suspect the biggest benefit of "balanced hp cables" is the elimination of crosstalk from shared ground return inherent in conventional 3-wire hp cables and shared ground contact resistance in TRS jacks. These are both measurable phenomena.

Hi Andrew

So the recommendation to use balanced for best performance is really for the headphones output, i.e. headphones cables?

It's not much to do with the input side, where RCA and XLR input have less effect on headphones output crosstalk?

Specifically asking about the THX 789 amp of course.
 
Last edited:

AndrewMason

Member
Technical Expert
Joined
Oct 29, 2018
Messages
46
Likes
147
Hi Andrew

So the recommendation to use balanced for best performance is really for the headphones output, i.e. headphones cables?

It's not much to do with the input side, where RCA and XLR input have less effect on headphones output crosstalk?

Specifically asking about the THX 789 amp of course.
Hi Music1969.

For Output:
I recommend use 4-wire headphone cables, and then use either XLR-4 BAL out or TRS out - both very similar.
TRS out has slightly lower noise, so that's probably best for sensitive IEMs.
XLR-4 has of course 2x Vswing & 4x Pout so that's probably best for max SPL from really insensitive phones.
You can't go wrong with either output so don't sweat it.

For Input
XLR w/ BAL DAC preferred.
Else use RCA to XLR cables with the separate ground return I mentioned earlier.
Else use RCA cables that are short and have heavy copper shield.
 

Roen

Addicted to Fun and Learning
Joined
Oct 14, 2018
Messages
681
Likes
247
Hi Music1969.

For Output:
I recommend use 4-wire headphone cables, and then use either XLR-4 BAL out or TRS out - both very similar.
TRS out has slightly lower noise, so that's probably best for sensitive IEMs.
XLR-4 has of course 2x Vswing & 4x Pout so that's probably best for max SPL from really insensitive phones.
You can't go wrong with either output so don't sweat it.

For Input
XLR w/ BAL DAC preferred.
Else use RCA to XLR cables with the separate ground return I mentioned earlier.
Else use RCA cables that are short and have heavy copper shield.
4-wire TRS means negatives on both sides connect to shared ground?
 

AndrewMason

Member
Technical Expert
Joined
Oct 29, 2018
Messages
46
Likes
147
4-wire TRS means negatives on both sides connect to shared ground?
Yes, separate ground wires for L and R, and they connect to plug ground inside the TRS plug itself. Like this:
1544217611426.png
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
Hi Music1969.

For Output:
I recommend use 4-wire headphone cables, and then use either XLR-4 BAL out or TRS out - both very similar.
TRS out has slightly lower noise, so that's probably best for sensitive IEMs.
XLR-4 has of course 2x Vswing & 4x Pout so that's probably best for max SPL from really insensitive phones.
You can't go wrong with either output so don't sweat it.

For Input
XLR w/ BAL DAC preferred.
Else use RCA to XLR cables with the separate ground return I mentioned earlier.
Else use RCA cables that are short and have heavy copper shield.

Thanks Andrew. Crystal clear now
 

AndrewMason

Member
Technical Expert
Joined
Oct 29, 2018
Messages
46
Likes
147
I see with headphones you could possibly run 3 wires all the way through, but with IEMs, you're pretty much forced to use 4 wires?
IEMs could have 3 or 4 wire cables. It varies by cable. You can usually tell just by looking at the shape of the jacket.
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
IEMs could have 3 or 4 wire cables. It varies by cable. You can usually tell just by looking at the shape of the jacket.

Hi Andrew

Can you or anyone help by looking at the jack here for my MrSpeakers AEON Closed - is this a 3 or 4 wire headphones cable?

What specific feature differentiates between 3 and 4 wire cable?

IMG_3219.JPG


IMG_3220.JPG
 
Last edited:

Roen

Addicted to Fun and Learning
Joined
Oct 14, 2018
Messages
681
Likes
247
Hi Andrew

Can you or anyone help by looking at the jack here for my MrSpeakers AEON Closed - is this a 3 or 4 wire headphones cable?

What specific feature differentiates between 3 and 4 wire cable?

View attachment 18530

That’s just the plug, you’d have to show the entire cable.

I’m trying to picture how a 3-wire IEM is cabled.
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
That’s just the plug, you’d have to show the entire cable.

I’m trying to picture how a 3-wire IEM is cabled.

Noted, I hadn't finished editing my post to include the 2nd pic.

Updated now above.
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
Hi Music1969.

For Output:
I recommend use 4-wire headphone cables, and then use either XLR-4 BAL out or TRS out - both very similar.
TRS out has slightly lower noise, so that's probably best for sensitive IEMs.
XLR-4 has of course 2x Vswing & 4x Pout so that's probably best for max SPL from really insensitive phones.
You can't go wrong with either output so don't sweat it.

For Input
XLR w/ BAL DAC preferred.
Else use RCA to XLR cables with the separate ground return I mentioned earlier.
Else use RCA cables that are short and have heavy copper shield.

Hi Andrew

One final question on the quote above if you don't mind.

Regarding crosstalk specifically (and I know it's nothing to worry about, it measures very well with the THX 789 for all use cases):

Is the final headphones output crosstalk measurement more dependant on the headphones out cable used? Or the input cable used (RCA vs XLR)? Or is it equally dependant on input and output cables used? For the THX 789 specifically.

Cheers
 
Last edited:

AndrewMason

Member
Technical Expert
Joined
Oct 29, 2018
Messages
46
Likes
147
Hi Andrew

One final question on the quote above if you don't mind.

Regarding crosstalk specifically (and I know it's nothing to worry about, it measures very well with the THX 789 for all use cases):

Is the final headphones output crosstalk measurement more dependant on the headphones out cable used? Or the input cable used (RCA vs XLR)? Or is it equally dependant on input and output cables used? For the THX 789 specifically.

Cheers
Unbal vs bal input doesn't change crosstalk.
Primarily 3wire headphone output cable and secondarily the TRS output jack shield contact resistance are the biggest contributors to crosstalk.
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
Unbal vs bal input doesn't change crosstalk.
Primarily 3wire headphone output cable and secondarily the TRS output jack shield contact resistance are the biggest contributors to crosstalk.

Thanks again Andrew. Crystal clear
 

Draculr

Member
Joined
Dec 9, 2018
Messages
31
Likes
46
I may have missed it earlier in the thread but can this unit be used as a pre-amp for powered monitors or is the output fixed?
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
Aeon Closed is 4 wire.

I asked MrSpeakers about their SE/unbalanced TRS cable.

Me: "Andrew Mason of the THX 789 headphone amp says: "4-wire TRS has separate ground wires for L and R, and they connect to plug ground inside the TRS plug itself ".

Does the single ended 3.5mm cable of the Aeon CLOSED classify as 4-wire TRS? Or is it a 3-wire TRS?"

MrSpeakers: "TRS (unbalanced) cables have 1 ground in the cable. TRRS (balanced) cables have separate ground wires for L + R. The termination of the cable is what determines this not the plugs that go into the headphones.

I believe Andrew has his terminology slightly wrong. He is talking about a TRS vs. a TRRS cable. Our 3.5mm cables are TRS."


But when I look at the connectors on their site:

Screen Shot 2018-12-11 at 10.09.08 am.png


So it does appear they have separate L and R ground going into the headphones for single ended cables.

If these ground wires terminate to a single wire, is this still classed as a 4-wire TRS?

Confused :-( @AndrewMason
 

AndrewMason

Member
Technical Expert
Joined
Oct 29, 2018
Messages
46
Likes
147
I asked MrSpeakers about their SE/unbalanced TRS cable.

Me: "Andrew Mason of the THX 789 headphone amp says: "4-wire TRS has separate ground wires for L and R, and they connect to plug ground inside the TRS plug itself ".

Does the single ended 3.5mm cable of the Aeon CLOSED classify as 4-wire TRS? Or is it a 3-wire TRS?"

MrSpeakers: "TRS (unbalanced) cables have 1 ground in the cable. TRRS (balanced) cables have separate ground wires for L + R. The termination of the cable is what determines this not the plugs that go into the headphones.

I believe Andrew has his terminology slightly wrong. He is talking about a TRS vs. a TRRS cable. Our 3.5mm cables are TRS."


But when I look at the connectors on their site:

View attachment 18645

So it does appear they have separate L and R ground going into the headphones for single ended cables.

If these ground wires terminate to a single wire, is this still classed as a 4-wire TRS?

Confused :-( @AndrewMason
If we're being specific, then TRS is a plug type. As in Tip Ring Sleeve. Not a good way of describing how a wire bundle is constructed.

Regarding cables to minimize crosstalk, you'll want 4 wire type where the Left and right have separate ground wires all the way from the ears to the TRS plug Sleeve where they must join. That'll eliminate the largest contributor to crosstalk in a TRS setup: the shared ground return.
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
Regarding cables to minimize crosstalk, you'll want 4 wire type where the Left and right have separate ground wires all the way from the ears to the TRS plug Sleeve where they must join.

Is a simpler way to describe it @AndrewMason :

3-wire TRS cable is the typical Y-configuration headphones cable, where you have a single cable from the TRS plug and then at some point along the length of the cable, this splits off into 1 cable to each ear.

4-wire TRS cable is a V-configuration, where L-ground and R-ground split off from the TRS plug itself, running separately all the way to the ears.

Is that a good description of the differences between 3-wire and 4-wire TRS?
 
Last edited:
Top Bottom