I don't understand this TRRRS cable pinout...
Sep 23, 2019 at 9:11 PM Thread Starter Post #1 of 9

rambomhtri

100+ Head-Fier
Joined
Jun 17, 2015
Posts
203
Likes
59
So, I got a WORKING but damaged TRRRS cable from a friend and I'm trying to repair some damaged parts in the cable (the external cloth/fabric that covers the inside cables is broken here and there). The cable works though, but it looks broken.

So, first I have to remove the back part of the jack, but I've tried as hard as I can and I can't do it, it's stuck and can't unscrew it at all (if it is that it's screwed to the TRRRS). I've tried with a pair of pliers, covering the jack with rubber/cloth, and still that thing won't move. I got very frustrated... So, I might end up buying a TRRRS plug, unless someone tells me how the heck this thing can be taken apart.

Now, the real problem is this one: I know how stereo cables work, I've repaired thousands of cables, with and without mic, I know the CTIA or OMTP standards and how to connect the pins. I've read and know theoretically how balanced cables work: in the music device you split the channel signal into 2 different cables/pins, in one of the cables you invert the signal, in the other cable you have the original signal; in the headphone's end you invert the inverted signal, you sum both signals and I suppose you then reduce it 50% to get the original signal. All of this is to reduce noise caught in the middle of the cable.
So, I believe you need:
PIN 1: original left channel
PIN 2: inverted left channel
PIN 3: original right channel
PIN 4: inverted right channel
PIN 5: ground (you mix the ground of the 2 channels)

So, I've checked the cable with a multimeter and in the headphones end I only have 4 connectors: 2 in the left channel and 2 in the right channel. Each pin of the jack plug is connected to one of those 4 connectors, but the sleeve of the jack plug is not connected to anything, and I don't understand how this balanced cable works. If I only could remove the jack cover and see the inside of it, I might understand, but anyways, none of this makes sense. Where's the ground to close the circuit? How in heavens this works?

By the way, the fabric cover is broken in one spot and I can see that there are only 4 cables inside the cable. Nothing makes sense...

Here's the schematic so you understand my problem:
123456.png

So, the TRRRS is:
T: left channel inner pin/cylinder (green)
R: left channel pin/cylinder cover (light green)
R: right channel inner pin/cylinder (red)
R: right channel pin/cylinder cover (pink)
S: nothing? ???

Can anyone help me?
The cable looks like this one (it's for a Shure SRH1540 with a Sony Walkman MDR-Z1R I believe):
Shure_SRH1540_balanced_cable_25mm_trrs_1024x1024.jpg


I'm also assuming that all the cable has no electronics inside (sounds dumb but you never know), I mean, all the work with the signals is done in the Audio player and headphone, I guess. This makes me ask this question:

A digital audio player is totally capable of splitting the left channel signal into 2 different signals, one of them inverted, and send them through 2 pins of the plug. Same with right channel. Total of 4 signals. Still don't understand in this cable where is ground and how the circuit is closed. Anyways, I don't understand neither how the headphone inverts one of the signals for each channel.
Does that mean that "balanced capable" headphones are able to invert one of the signals?
Does that mean that these headphones have electronics inside to invert one signal? What powers that circuit?
How the headphone knows if a balanced or unbalanced cable is connected?
 
Last edited:
Sep 23, 2019 at 10:08 PM Post #2 of 9

jmpsmash

100+ Head-Fier
Joined
Aug 30, 2001
Posts
237
Likes
63
Location
Santa Clara, CA
Strictly speaking, you are correct that headphones don't need the ground. Although I can also see that headphone cables can optionally use the ground for shielding purposes.

The other use case is that it can also be used as a generic stereo balanced connector, say, connecting to a preamp/poweramp. In that case, it is essential to have a ground reference. Normal XLR interconnect have a ground reference for that exact purpose.
 
Last edited:
Sep 23, 2019 at 11:29 PM Post #4 of 9

jmpsmash

100+ Head-Fier
Joined
Aug 30, 2001
Posts
237
Likes
63
Location
Santa Clara, CA
lol. my apologies.

the driver of a headphone is simply just a coil with 2 wire ends, when there is a voltage between the 2 wires, it will generate a magnetic field and moves the driver.

the key is that there only need to be a voltage difference between the 2 wires, it does need any ground reference.

so in normal single ended, it is positive - ground = positive (where ground = 0v)

in differential, it is positive - inverted = 2x positive (inverted is just -positive)

so the ground wire is not needed.
 
Sep 24, 2019 at 5:59 AM Post #5 of 9

rambomhtri

100+ Head-Fier
Joined
Jun 17, 2015
Posts
203
Likes
59
So there's no inverted signal at all. A ground is ALWAYS needed to close the circuit. In a balanced configuration, you SEND 2 signals, one original and another inverted, to the cable BEFORE the coil. Then, before the coil, these 2 signals must be sum and converted into one signal that moves the driver. After the coil, that cable returns to the device to close the circuit. That cable is what I call ground, and in this case with only 5 pin, the returning wires of the 2 coils must join/mix together and be soldered to the last pin of the plug.
The only thing that I can think of is that it doesn't invert a signal at all, and the only difference with am unbalanced cable is that this cable (and headphones) simply have the ground of the 2 coils separated, one pin for each coil. But, this is not at all what I read when learning about balanced cables. Looks like a scam.
 
Last edited:
Sep 24, 2019 at 8:11 PM Post #6 of 9

jmpsmash

100+ Head-Fier
Joined
Aug 30, 2001
Posts
237
Likes
63
Location
Santa Clara, CA
Oh i see the confusion. Ground is just a reference. there is no requirement that any of the 2 terminals going to the driver be at ground.

Pardon my little diagram, but i hope it clears up the confusion. the ground is in between the non-inverting and inverting, and the circular arrow is where the current would flow. but I hope that clears up some confusion.

However, it is correct to say that, from the point of view of the driver, there is no true ground reference and why would a balanced signal be any different than single ended. go figure.

20190924_170408.jpg
 
Sep 24, 2019 at 10:19 PM Post #8 of 9

ericj

Headphoneus Supremus
Joined
Aug 2, 2005
Posts
8,262
Likes
151
Your confusion arises from having identified the 5th conductor as "ground"

It's not really ground. It's shield.

Balanced signalling is used in PA systems because of the mix of sometimes-very-small signals like microphones, the very long cable runs that happen, and the complexity of wiring that leads to a high potential for interference.

It's a differential signal pair. A signal and an inverted signal that get summed, which means that any interference that comes across the cable is likely to be common to both signals and will equal nothing when it is summed.

A dynamic microphone naturally produces a "balanced" signal. A positive and an inverse which we can naturally think of as negative.

You CAN ground the negative side, and it will still work. But if you don't have to, you get better signal integrity.

The output of a signal transformer is similarly naturally "balanced". Unless and until you tie the 'negative' side of the secondary to ground. And yes sometimes they are center tapped, and you can ground the center tap as a reference.

PA gear with XLR connectors often have a "ground lift" switch. Ideally, the "ground" on an XLR cable is only connected on one end, typically the signal source, and is connected to the cable shield. If for some reason it is connected to both ends and this causes a ground loop, you hit the ground lift switch on one end to disconnect it.

A headphone driver is almost exactly like a dynamic mic. In fact, the lore is that the original 2000-ohm HD414 started out as literally two microphone capsules on a headband.

Voltage is a potential between two points. Neither of those points has to be "ground" and there does not need to be a "Ground Reference".

The positive and negative signals will do a fine job of pushing around the voice coil in a headphone driver. I'm actually not 100% on why people prefer to drive high end dynamic headphones balanced. Maybe it's an increased damping factor they like?
 
May 21, 2020 at 2:24 AM Post #9 of 9

Gogoawy

New Head-Fier
Joined
Apr 2, 2020
Posts
4
Likes
9
Location
Vietnam
Your confusion arises from having identified the 5th conductor as "ground"

It's not really ground. It's shield.

Balanced signalling is used in PA systems because of the mix of sometimes-very-small signals like microphones, the very long cable runs that happen, and the complexity of wiring that leads to a high potential for interference.

It's a differential signal pair. A signal and an inverted signal that get summed, which means that any interference that comes across the cable is likely to be common to both signals and will equal nothing when it is summed.

A dynamic microphone naturally produces a "balanced" signal. A positive and an inverse which we can naturally think of as negative.

You CAN ground the negative side, and it will still work. But if you don't have to, you get better signal integrity.

The output of a signal transformer is similarly naturally "balanced". Unless and until you tie the 'negative' side of the secondary to ground. And yes sometimes they are center tapped, and you can ground the center tap as a reference.

PA gear with XLR connectors often have a "ground lift" switch. Ideally, the "ground" on an XLR cable is only connected on one end, typically the signal source, and is connected to the cable shield. If for some reason it is connected to both ends and this causes a ground loop, you hit the ground lift switch on one end to disconnect it.

A headphone driver is almost exactly like a dynamic mic. In fact, the lore is that the original 2000-ohm HD414 started out as literally two microphone capsules on a headband.

Voltage is a potential between two points. Neither of those points has to be "ground" and there does not need to be a "Ground Reference".

The positive and negative signals will do a fine job of pushing around the voice coil in a headphone driver. I'm actually not 100% on why people prefer to drive high end dynamic headphones balanced. Maybe it's an increased damping factor they like?
thank you very much, I was working to make my own cable for my HD660s and scratching my head to find a way for the "Shield" or "Ground" to be presented in it. Reading you cmt I understand that I could solder the sleeve of TRRRS plug to the Shield or Ground wire right?
 

Users who are viewing this thread

Top