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Review and Measurements of Massdrop THX AAA 789 Amp

AndrewMason

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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?
Hi Music1969. You've got it!
Your description of 4-wire cable is correct.

3-wire cable exists in 2 flavors, both bad:
type a) Shared GND + Left + Right go from TRS to a midpoint, where left and right split off. Ground splits into two. This is getting pretty rare and may only exist on some cheaper headphones.
type b) Shared GND + Left + Right go from TRS to one earcup. Inside the earcup, the shared ground connects to that transducer, and also to a ground wire coming through the headband from other transducer. e.g. Oppo PM3, NAD HP50 VISO, etc etc.
In both cases there's a portion of cable copper sharing ground return current for both transducers. That's the crosstalk mechanism. Current from one transducer will cause a voltage drop on this shared ground path, therefore causing the equal and opposite voltage to appear across the other transducer. The key to avoiding this is buying cables that have no portion of the cable carrying shared ground current. i.e. "4-wire".
 

Music1969

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Hi Music1969. You've got it!
Your description of 4-wire cable is correct.

Woohoo! Thanks Andrew

3-wire cable exists in 2 flavors, both bad:
type a) Shared GND + Left + Right go from TRS to a midpoint, where left and right split off. Ground splits into two. This is getting pretty rare and may only exist on some cheaper headphones.

This is indeed the case with my MrSpeakers AEONs... so I need to seek a 4-wire TRS cable. Or try their balanced cable when my THX 789 arrives in the next week or two. And see if I can use Gain #1 past 12 o'clock for example or if it's too loud with the balanced headphones cable.

In both cases there's a portion of cable copper sharing ground return current for both transducers. That's the crosstalk mechanism. Current from one transducer will cause a voltage drop on this shared ground path, therefore causing the equal and opposite voltage to appear across the other transducer. The key to avoiding this is buying cables that have no portion of the cable carrying shared ground current. i.e. "4-wire"

Got it! Thanks again for you patience with me here. I'm sure this helps others reading this too, that may have misunderstood the key differences and the mechanisms.

Much appreciated!
 

derp1n

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This is indeed the case with my MrSpeakers AEONs... so I need to seek a 4-wire TRS cable. Or try their balanced cable when my THX 789 arrives in the next week or two. And see if I can use Gain #1 past 12 o'clock for example or if it's too loud with the balanced headphones cable.
Or just use what you have, because the difference isn't going to be audible.

And the Aeon cable is 4-wire. Look at the way it's constructed.
 

Music1969

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And the Aeon cable is 4-wire. Look at the way it's constructed.

It's a Y-config, not a V-config. Also confirmed by MrSpeakers that it shares ground along most of the cable.

The L-ground and R-ground don't split off from the TRS plug itself and go separately all the way to the ears.. which is the requirement for a 4-wire TRS (V-config).
 

derp1n

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It's a Y-config, not a V-config. Also confirmed by MrSpeakers that it shares ground along most of the cable. The L-ground and R-ground don't split off from the TRS plug itself..
If you insist. I've looked at mine, I know exactly what I have.
 

Music1969

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If you insist. I've looked at mine, I know exactly what I have.

I'm only here to learn, not insist. I can only go by the clarification from Andrew above.

What features makes you think it's 4-wire TRS?

The 4-pin connectors in each ear is not enough to conclude this (from what I've learnt above...).

Appreciate your help.

Here is my cable. 1 cable from the TRS plug becomes 2 cables at the splitter. It's not 2 cables running from the TRS plug all the way to the ears.

PS: yes right earpad needs replacing ASAP :D

IMG_3231.jpg
 
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derp1n

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RayDunzl

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1 cable from the TRS plug becomes 2 cables at the splitter.

Are there 3 or 4 wires in the bottom of the Y?

Does the cover of the TRS plug unscrew so you can look inside it?
 
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maxxevv

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Point is, there is a R+, R- and L- and L+ wire on the two sides after the split.

At the y-split, these 4 wires continue until you reach the 3 pin connector.

There R+ and L+ will each have their own connections soldered to the plug.

Then the L- and R- will be soldered together at the "Earth" pin of the plug.

Hence, if you cut away the 3-pin plug, you still have a 4 wire cable.

I have never seen a twin driver connected cable terninated at the y-split.

The only headphone cables I have seen that carry only 3 wires are the ones that terminate on one side of the headphone.
 

Music1969

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Point is, there is a R+, R- and L- and L+ wire on the two sides after the split.

But this is the point @AndrewMason makes above:

"The key to avoiding this is buying cables that have no portion of the cable carrying shared ground current. i.e. "4-wire""

So you need to visually see 2 cables going all the way from TRS plug to the ears -i.e V-config.

If there's a Y-config (with a split) then they are sharing ground for the majority of the length of the cable - the mechanism for crosstalk (per Andrew above).

Unless I could un-screw the TRS plug and see 4-wires, i.e. separate grounds running away from the plug (and insulated from each other) but I can't @RayDunzl

I'm only quoting Andrew above. I'm definitely no expert.
 

derp1n

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He's commenting about the dual entry cables there for alpha and ether. Doesn't apply to Aeon...

https://www.mrspeakers.com/shop/accessories/dum-dual-entry-cables.html
Really? In the Aeon thread? Where people are specifically asking him about the Aeon cables? More specifically, even, whether they can reterminate the cables to XLR-4?

These cables: https://www.mrspeakers.com/shop/acc...mmer-cable-for-aeon-and-ether-headphones.html

The DUAL ENTRY Aeon cables?

You're obviously very determined to argue about something you know very little about. Please give it a rest.
 

Music1969

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Really? In the Aeon thread? Where people are specifically asking him about the Aeon cables? More specifically, even, whether they can reterminate the cables to XLR-4?

These cables: https://www.mrspeakers.com/shop/acc...mmer-cable-for-aeon-and-ether-headphones.html

The DUAL ENTRY Aeon cables?

You're obviously very determined to argue about something you know very little about. Please give it a rest.

The dual entry Aeon cables are nowhere to be found under their 'cables' section:

https://www.mrspeakers.com/shop/accessories/cables.html

Here you'll only see the dual entry for alpha and ether... Pretty sure that's a reasonable place for someone to look (FFS!).

The link to the dual entry Aeon cables hasn't been put in the general cables page... crikey.

The standard TRS cable that comes with Aeon is not the dual entry type... that's why there's a separate page for it as you've found...
 

derp1n

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The dual entry Aeon cables are nowhere to be found under their 'cables' section:

https://www.mrspeakers.com/shop/accessories/cables.html
Capture.png

Here you'll only see the dual entry for alpha and ether... Pretty sure that's a reasonable place for someone to look (FFS!).

The link to the dual entry Aeon cables hasn't been put in the general cables page... crikey.

The standard TRS cable that comes with Aeon is not dual entry. Crikey...
Capture2.JPG
 

derp1n

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IMG_3231.jpg
 

Roen

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Hi Music1969. You've got it!
Your description of 4-wire cable is correct.

3-wire cable exists in 2 flavors, both bad:
type a) Shared GND + Left + Right go from TRS to a midpoint, where left and right split off. Ground splits into two. This is getting pretty rare and may only exist on some cheaper headphones.
type b) Shared GND + Left + Right go from TRS to one earcup. Inside the earcup, the shared ground connects to that transducer, and also to a ground wire coming through the headband from other transducer. e.g. Oppo PM3, NAD HP50 VISO, etc etc.
In both cases there's a portion of cable copper sharing ground return current for both transducers. That's the crosstalk mechanism. Current from one transducer will cause a voltage drop on this shared ground path, therefore causing the equal and opposite voltage to appear across the other transducer. The key to avoiding this is buying cables that have no portion of the cable carrying shared ground current. i.e. "4-wire".
a) sounds like a better design than b)
 
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