AKG K371 Review (closed back headphone)

[Music1969]

The connector suggests this should be possible (4-pin mini XLR) which means it won't accept 3-pin mini XLR.
The strange thing is that the 3 cables that come with it are all TRS.
However, as this is a BT headphone as well it is highly likely the - of both drivers are connected making balanced impossible.
Maybe the plan was to also use the K371BT's microphone and maybe even one button remote using a 3.5mm TRRS but ditched the idea.
Maybe AKG plans to launch all future headphones with 4 pin connectors so owners can use headphones balanced as well... maybe AKG saw the balanced light ... finally.
We might know when new headphones come out.
I would guess one pin is not connected though.

Hi @solderdude

Does the K371 (not BT) stock cable have all 4 conductors insulated end to end?

No shared 'ground' after the 3.5 plug, to the other end?

I know it starts with 3.5mm plug at one end and ends in 4-pin mini XLR at other end but don't know if conductors are all insulated all the way between ?

 

[solderdude]

Its 3-wire (the used mini XLR has 3 pins)

 

[Music1969]

Its 3-wire (the used mini XLR has 3 pins)

View attachment 165606

So this means shared ground all the way then?

Not the best thing ?

Unless the left -ve and right -ve are insulanted until they meet at the ends? Which would be fine ?

 

[solderdude]

Shared grounds all the way up to the headphone.
Not the best thing.
A recurring theme in Beyerdynamic and AKG headphones alas.

 

[Music1969]

Shared grounds all the way up to the headphone.
Not the best thing.
A recurring theme in Beyerdynamic and AKG headphones alas.

Damn, and the problem is the 3-pin plug limits DIY options to do better

 

[solderdude]

Exactly. No idea why they did not adopt a 4 pin mini XLR. I guess they do not see the benefits.

 

[Music1969]

Exactly. No idea why they did not adopt a 4 pin mini XLR. I guess they do not see the benefits.

Having the grounds insulated between the ends helps a little? Or not really?

If doing DIY cable.

 

[solderdude]

You will just half the total cable resistance.

Better to make a cable with a screen and use that for the return wire. The only thing of importance is the common return wire (ground) resistance must be as low as possible. A screen can be very low resistance.

 

[Music1969]

Exactly. No idea why they did not adopt a 4 pin mini XLR. I guess they do not see the benefits.

Bizarrely the K371-BT has 4 pin XLR !

AKG K371-BT Bluetooth Studio Headphones Review

A little bit louder and a little bit worse

xander51.medium.com

 

[Phorize]

Damn, and the problem is the 3-pin plug limits DIY options to do better

I was looking at this, it’s a shame as the long stock cable is so microphonic it renders a reasonable headphone borderline unusable.

 

[solderdude]

Bizarrely the K371-BT has 4 pin XLR !

AKG K371-BT Bluetooth Studio Headphones Review

A little bit louder and a little bit worse

xander51.medium.com

View attachment 166014

I have no idea how that is wired. The cable for it is 3.5mm TRS. So possibly they either intended to also have a remote/mic function (the 4th pin) or for some reason each driver is balanced out.
When AKG decided to use bridged amping (to gain 6dB headroom using BT) this could be logical.

Maybe an ASR member owning one could find out which pins have what resistance between them when switched off ?

 

[LTig]

I have no idea how that is wired. The cable for it is 3.5mm TRS. So possibly they either intended to also have a remote/mic function (the 4th pin) or for some reason each driver is balanced out.
When AKG decided to use bridged amping (to gain 6dB headroom using BT) this could be logical.

Maybe an ASR member owning one could find out which pins have what resistance between them when switched off ?

I measured the cable, FWIW. The XLR connector has markings 1, 2, and 3 for the sockets in the circle, but none for the socket in the center which I shall name as 4 (see Rean RT4FC-B). Connections are:

• TRS tip -> XLR 1
• TRS ring -> XLR 2
• TRS sleeve -> XLR 3 and 4

 

[solderdude]

Thanks... the question is if XLR 3 and XLR 4 in the headphone itself are also connected or only in the cable.
When not connected ... XLR1 connects to XLR ?
XLR2 connects to XLR ?

 

[Berwhale]

Thanks... the question is if XLR 3 and XLR 4 in the headphone itself are also connected or only in the cable.
When not connected ... XLR1 connects to XLR ?
XLR2 connects to XLR ?

Discussed here: https://www.reddit.com/r/headphones/comments/gz24ud

 

[solderdude]

Seems like pin 3 is not connected. No idea why AKG decided to use 4 pins if they did not connect the 3 pin. Because of this you cannot use the K371BT with any of the 3 pin cables, used by AKG and Beyerdynamic. On the regular 3-pin the 1-pin is ground, 2 = R and 3 = L
Weird decision to also change the pinning as now you can't use the K371BT cable on any other 3-pin mini XLR headphone.

At least the Beyer DT177X uses a 4 pin and can be used balanced but this is a Drop product, made by Beyerdynamic.

(Edit... corrected as not pin 4 is not connected but pin 3 is not connected)

 

[Blumlein 88]

Seems like pin 4 is not connected. No idea why AKG decided to use 4 pins if they did not connect the 4th pin. Because of this you cannot use the K371BT with any of the 3 pin cables, used by AKG and Beyerdynamic.
Weird decision.

At least the Beyer DT177X uses a 4 pin and can be used balanced but this is a Drop product, made by Beyerdynamic.

The 4th pin is likely carrying the microphone signal (off the sleeve maybe). There is a small mic built into the left earcup.

I saw someone mention a Fantasia 4 pin cable (which has a microphone built into the cable). The reason to replace is the Fantasia is more supple and doesn't cause noise rubbing on your shoulder. The stock cable is stiff and you hear movement against your shoulder. I don't know how that works with the existing microphone. I may give that Fantasia cable a try and I'll let you know if it works. They should have used a right angle connector, but I've not found one for mini XLR 4 pins.

 

[solderdude]

Usually this means also there is a remote functionality (skip, play, stop) and there should be some minimal resistance for the mic opposite to ground.
From the mentioned thread it seems like pin 4 3 is simply not connected.

The internal mic is probably already connected to the BT PCB and I figure it wasn't possible to use the mic without power (passive mode).

Another option is that the 3-pin is used to disconnect the BT output circuit from the drivers the moment the cable is plugged in or such functionality.
One would expect to see at least some resistance or measure a small voltage opposite ground.

In any case it does not look like a balanced input.

 

[Blumlein 88]

I just checked out my cable. Pin 3 and the center pin 4 are both connected to the sleeve or ground. None of the supplied cables are of the TRRS type so they connect pin 4 to pin 3 and only have TRS output.

I don't see how the microphone can work this way. They clearly tell you it has a microphone for VOIP or phone or Vlogging. I wonder if it only works if you replace the cable?

Update some measurements. Pin 3 and 4 on the headphones has 32.7 ohms between them.

 

[solderdude]

The mic works but only via BT.
It's the same with the JBL TUNE 710.
Weirdly enough it has a cable with TRRS 3.5mm connector suggesting the mic/remote in the HP can be used on phones etc but the supplied cable ends in a 3 pin TRS jack in the HP itself. Ring2 and sleeve are simply connected in the TRRS plug.
This is emulating the play/pause button (which shorts the R2 and sleeve).
In some phones plugging in or out the plug could trigger the pause button.

The TRRS plug, wired this way will ensure there will be sound on Apple and Android devices and most 3.5 to 6.3 mm adapters will work.

 

[Blumlein 88]

Seems strange they'd suggest this for vlogging if the mic only works over BT. I'll have to try all that out on mine. I've only used the BT a few times to see it works and to compare sound over BT and wire.