[GUIDE] Balanced AKG K702 with detachable 4-pin mini-XLR cable

This is my first audio DIY, as well as my first guide here on Head-Fi.

I posted a while ago about how feasible this project would be, and since then, I've went out and bought all the stuff I needed to try this out. And the results: IT WORKS!




[size=small]Introduction and Idea[/size]
Balanced operation requires 4 channels going into your headphones (L+, L-, R+, R-). The stock AKG K702 has a 3-pin mini-XLR connector for detachable cables, and there exists many cables from people like ALO that replace the stock detachable cable that fit into this slot. However, the 3-pin forces only 3 wires (channels) going in to the headphones.

Thus, I got the idea to replace the stock 3-pin with a 4-pin connector. That way, I can actually get 4 channels into the headphones, and it keeps the detachable design that I like about the K702. I also built the cable from 4-pin mini-XLR to 4-pin XLR as well, which was relatively simple.


[size=small]Warnings and Notes[/size]
As a warning, this mod involves opening up the side of the headphones and pressing out the stock 3-pin mini-XLR jack, which is not a delicate matter. Specifically the part where you have to press out the stock jack. If you plan on doing this mod, you should be ready to order spare parts from AKG. I sure did.

Also, excuse me for not posting pics of the entire process, I got too excited when I got all the materials, and never stopped to take photos as I went along. I'll try to be comprehensive in my descriptions of what I did to make up for it.


[size=small]Materials and Tools[/size]
All materials used for this project was bought from Redco Audio, who offers some great prices for a lot of DIY projects.

Cable: 6ft of Mogami W2893 Miniature Quad Mic Cable
Heat Shrink: 6" of 1/4" Heat Shrink
Connectors:
Redco male 4-pin mini-XLR
Redco female 4-pin mini-XLR
Neutrik NC4MX-B (4-pin male XLR)
Neutrik NC4FX-B (4-pin female XLR)
Neutrik NP3C-B (1/4" TRS plug)

I had my own set of tools, but here's what you need for this mod:
soldering iron, solder, wire stripper and cutter (or a sharp knife!), multimeter (for continuity check), superglue, press (or is there some other way?)


[size=small]Part 1: Opening Up the Left Side[/size]
This is the first scary part. To get access to the wires, start by removing the left grille. Take a thumbtack, twist it counter-clockwise, and pull out. Be careful, you don't need to turn much for it to come out! And it also doesn't pull out very easily, so don't expect it to come falling off when you've turned it.

Once you open that, you should see something like this:


Next, remove the two screws on the ear cup. Now to remove the ear cup and get access to the wires, you must pinch the sides of the ear cup and pull outwards. This part is quite hard, and you must use quite some force to get it out! You also have to unsnap the headband guides from the ear cup. This is probably the first scary part. Once you get that you'll get to something like this:

(this image is actually after the mods, the wiring's already done in this one)


[size=small]Part 2: Desolder Internal Wires[/size]
I don't have a proper picture for this, as the below picture was taken after I did the mod. But the stock AKG K702 has the common ground (L-, R-) soldered together. To get balanced configuration, we need to separate the two channels. If I remember correctly, the two ground wires are both white. The next picture shows which lead is which channel:


Also desolder the wires from the ear cup's stock 3-pin mini-XLR connector.


[size=small]Part 3: Press Out the Stock 3-pin Connector[/size]
Sorry I don't really have pictures for this. But the idea is to get the tiny little connector out (the small piece of plastic with the 3 pins through it). My roommate got the idea to use a press and a small metal rod to force it out of the ear cup. So we went to the machine shop and did so. We pressed the rod into the connector out through the cable slot in the ear cup. This was probably the scariest part of the entire project, but it worked out in the end. Though we got the ear cup a bit scratched up...

If there's any other way to remove it without brute force, please let me know!


[size=small]Part 4: Place in and Connect 4-pin Connector[/size]
First, take apart the male 4-pin mini-XLR connector, and there should be a small plastic piece with the 4 pins through it. This will replace the 3-pin one we removed.

First, solder the inner leads (the shorter ones) to the wires on the headphones. Refer to the above picture for which lead is which on the headphone. As for the pinouts for 4-pin XLR:
pin 1 - L+
pin 2 - L-
pin 3 - R+
pin 4 - R-

You should now have the 4-pin connector dangling from the side of the headphones. Now place the connector into the ear cup from the inside. This part is a bit delicate, so be careful. Once it's snugly in (for me, it didn't fully go in all the way like the previous 3-pin connector did), apply 2 or 3 drops of superglue to the sides of the connector on the inside of the ear cup.

The superglue makes sure that the connector doesn't wiggle when you connect a cable to it. I initially didn't apply the superglue, as I thought the connector was snug enough that it wouldn't wiggle, but when I tested it, it did. So do apply some superglue!




At this point, we're done with modifications to the actual phones. So, snap the earcup back into place (also kinda scary). Then replace the two screws, and replace the left grille we removed.


[size=small]Part 5: Build Cables[/size]
This part has probably been documented all over the place, so I won't go into excruciating detail. I took the 6ft of Mogami W2893 I got and cut it down to make an additional adapter to 1/4" TRS for single-ended operation.

For the main cable, we just want 4-pin female mini-XLR to 4-pin male XLR (the large one). Pretty simple to make, but there's a slight annoyance here. The mini-XLR connector doesn't fit the Mogami cable entirely (with all the insulation on). I could only fit the 4 internal wires through the hole, so I had to use some heat shrink to insulate this and provide a bit of strain relief. This is also why I stripped more from the mini-XLR side.

1. Slide on the strain reliefs and clamps from both connectors first! Don't be like me and forget to do so for one connection, and then have to desolder the plug to get them back on!
2. Slide on the 1/8" heat shrink onto the cable as well, we'll need this when we're done to insulate the 4 wires at the mini-XLR end.
3. Remove all the insulation from both ends. Get about 3/4" from the regular XLR side, and about 6/4" from the mini-XLR side. For the Mogami, this means the outer rubber, the thin shielding wires, the paper-like wrapping, and the cloth-like threads. We want just the 4 internal leads. Strip a tiny amount from these leads, maybe about 1/8" or so.
4. Assign a lead color to a pin number. I used Red - pin 1, Blue - pin 2, White - pin 3, Black - pin 4.
5. Solder leads from both ends to the connectors according to your color assignment from the previous step.
6. Use a multimeter to test for connectivity from one end to the other. Make sure no wires from different channels are touching internally.
7. Screw on the outer plug onto both ends.
8. Position the heat shrink over the bare 4 wires at the mini-XLR end. Use a heat gun (or in my case, a hairdryer) to heat it up, and it'll shrink and fit snugly around the wires to provide strain relief and insulation.

End Result:


I also made a balanced female 4-pin XLR to male 1/4" TRS adapter so I can still use my current SE amp. This one's more or less the same as the previous cable, just much shorter, and you must connect pin 2 and pin 4 (L- and R-) to the ground lead on the TRS connector. The TRS connector's leads are connected like this:
ground (L- and R-) goes to the shielding ring
L+ goes to the middle lead
R+ goes to the top lead

When connected to the other cable I made:



[size=small]Final Thoughts[/size]
In the end, the mod turned out pretty well, I think. I can't really comment on how the cable I built compares to the stock cable, as I can't really ABX it: the stock one doesn't fit onto the new 4-pin connector. I'm not really a cable believer (don't flame me, please <__<), but I am intrigued by balanced operation.

Now all that's left for me to do is save up money for a balanced amp like the LD MKVII+ and a balanced DAC too... sorry, wallet.

I hope this helps for anything thinking about balancing their pair of these wonderful headphones! Please offer some critique and/or comments! Wondering how I did for my first DIY mod...

Did you notice a huge difference in sound after you balanced them?

So I don't have a balanced amp to actually use them in balanced operation yet, if that's what you were wondering. If you're wondering if balancing them and using a balanced amp makes a huge difference in sound, I always like to refer to this thread:

http://www.head-fi.org/forums/f5/lit...lanced-463006/
and this post:
http://www.head-fi.org/forums/6475106-post140.html

If you're wondering whether the recable made a difference in SE operation, I can't really say. I don't really remember the sound of the stock cable, as I pressed out the 3-pin connector a few days before the materials for the recable arrived, so I didn't get to listen to them for a while. When I tried them after the recable, I had forgotten what they used to sound like. I guess I could try making a 4-pin mini-XLR to 3-pin mini-XLR adaptor to be able to use the stock cable again for ABX'ing, but that means getting more supplies.

Nice write up.

Suggestion for you since you went to all the trouble to keep the disconnect feature of the headphone why not instead of using an adapter for the TRS just make 2 cables for the headphone. 1 TRS and 1 XLR. This would make the cable much less bulky and reduce the number of contacts you have in the chain.

I was considering that, but decided that if I wanted a dedicated single-ended only cable (TRS), I might as well make a 4-pin mini-XLR to 3-pin mini-XLR adapter, and then plug in the stock cable into that. It seems more modular that way, so I could potentially even use other people's cable upgrades for the K702.

I do agree with you that the cable is bulky as hell though. Hopefully, I'll get that balanced setup sometime soon, so I can get rid of the adapters and go to audio nirvana. That and make my wallet cry in the corner.

I was googling mini 4 pin xlr, just to see what parts were available to think about doing this mod, and I found this thread!  Glad to hear it's possible, and I'll definitely give it a try sometime! Great Mod, and I can't believe there isn't more talk about this!

Quote:

elwappo99 said:

I was googling mini 4 pin xlr, just to see what parts were available to think about doing this mod, and I found this thread!  Glad to hear it's possible, and I'll definitely give it a try sometime! Great Mod, and I can't believe there isn't more talk about this!

Click to expand...

yeah really! lots of people including myself would have purchased the 701 just to retarminate if they wanted a cheap balanced K70X.. this almost as easy and no funds are lots switching up headphones!
 
Good to see someone has their thinking cap on!

I just finished my k702 balanced mod. Thanks castigar. I never get brave enough for this operation if your guide does not exist. I melded existing mini xlr with soldering iron and it's easily leave it's place without harm around it. So there is no need to use brutal force if you don't care waste existing xlr jack.

 
Quote:

ulyses said:

I just finished my k702 balanced mod. Thanks castigar. I never get brave enough for this operation if your guide does not exist. I melded existing mini xlr with soldering iron and it's easily leave it's place without harm around it. So there is no need to use brutal force if you don't care waste existing xlr jack.

Click to expand...

You used your soldering iron to dislodge the mini-XLR? Well I hope you were wearing a mask and not breathing in the fumes from burning plastic! But whatever works, right? I'll admit It's a lot more convenient than having to find a press. Good to hear that this guide I wrote almost a year ago is useful!

Yes it works. There weren't too much smoke actually. The part have different type of plastic than headphone's case. It's getting like coal after melded. And the only job is cleaning it with thin metal rod after that. 

I found the guide to dismantling the phones very usefull, thank you.
 
I would add that you should shield at least one channel in the cable as the amount of crosstalk between the wires in this cables would be significant, the CMR would negate the crosstalk, however, it would be best if it were not there in the first place.
 
 

These cables (the mogami 4 conductor) have individually shielded conductors, and manage pretty well without significant crosstalk for all manner of studio applications. 

going balanced alone eliminates crosstalk cause the negatives act as a ground cable as well. that's why older studio headphones always used a 4-conductor balanced wiring with either a 1/4'' balanced TRS jack or a Balanced DIN connector(DIN connector for european models).


anyways,congrats on the successful mod. i wish more headphones started making use of 4-pin XLR connectors. they're so versatile when you need it to be. have you tried making a 4-pin XLR to bare wire for speaker outputs? that can become very handy when your craving more power or need it.

I have not tried it, but I can't imagine it'd be too hard. And I definitely agree that 4-pin XLR should be used more, though I can see the large size of the connector being a disadvantage compared to other balanced connectors (like the one used on the RSA Protector). Though the larger connector does also mean it's easier to solder...

naw,not difficult at all to make a 4-pin XLR to bare wire cable. great using speaker outputs cause power is no concern and damping factor as well cause speaker output impedances are always close to 0 ohms if your worried about impedance matching if it's solid state. if you use tubes your gonna have to use a resistor at the speaker outputs cause tubes highly rely on their power transformer(s) for output impedance matching and it's the power transformer that gives the tubes it's output impedance. Solid state is doesn't matter if you stock 1000ohm headphones or 32ohms. it will match the impedance no problem if it's a good push-pull design.