Beyerdynamic Balanced Removable 4 Pin Mini XLR Mod

A client recently sent me one of my favorite headphones to modify, a Beyerdynamic DT770. The DT770, DT880, DT900, and similarly the T1, T5p, T70, and T90 are all intuitive to work with and respond well to new cables and mass loading.

Beyerdynamic DT770 - Pro 80 ohm version

This DT770 would be getting a removable cable mod, which includes the installation of a mini XLR in the headphone cup so the cable can easier be removed for transport or to perhaps have separate cables for portable and home use. The DT770 has room for a mini XLR jack on both the left and right cups, however this user preferred the simpler single ear input. Since I was already going through the trouble, I wired the headphone for balanced operation just in case he ever switches over to balanced listening in the future. The great thing about mini XLR jacks is they lock, so no need to worry about them slipping out like a 3.5mm or 2.5mm. Also, TRS connectors can loosen over time, however this is not as likely with the mini XLR connectors.

Below is a look at the interior driver. As you can see, the DT770 driver is unique in that it has a felt and plastic ring encircling the center, which reduces the sound wave reflection inside the cups.

DT770 driver and felt/plastic ring

Because the felt and plastic circle reach the plastic backing of the cups, any added mass damping should be clear of interaction. Below you'll note the Dynamat Xtreme installed is a small circle which is measured to fit neatly inside the cup and not cause any clearance issues with the driver. 

Dynamat Xtreme used as mass loading

Beyerdynamics used to come with a round hole, but it's square now that they've revised the manufacturing to some extent. I carefully increased the size of the hole diameter toward the round side of the cup with a Dremel to prevent the plug from getting in the way of the driver. The hole does not have to be absolutely round as the ridge on the mini XLR plugs will cover minor imperfections. 

Dremeled hole for 4 pin XLR mini jack

A three or four pin mini XLR jack can be used. In this case I used a four pin as I wanted the user to be able to upgrade to balanced down the line if he wanted, but in other cases, a three pin can be used as the ground is wired shared as default. Please note the position of the jack, if it is not close to the rounded edge like this is, the driver will not fit back in. Dremeling down the metal casing of the jack where it meets the driver may help a little bit, but will reduce the integrity of the jack if too much is taken off. 

Nice, clean fit

Wire should be run from one side of the headphone to the other as this is going to be single entry. A twisted pair of Zynsonix Xev silver clad wiring is prepped and sleeved with black polyolefin heatshrink tubing. 

Wire to run from one cup to the other

This can be wired however the user prefers, however I used the XLR standard (pin 1 = left +, pin 2 = left -, pin 3 = right +, pin 4 = right -). 

Wired with Zynsonix Xev silver clad wire

Before re-installation, the driver solder tabs are cleaned of the stock solder.

Solder tabs cleaned of original solder

The new Zynsonix Xev wires are installed using fresh Cardas silver content solder and the felt/plastic cups re-installed. 

Driver wired up and ready

The foam is reseated on top of the drivers and the earpads are reinstalled, so we have a nice clean 4 pin mini XLR input on our Beyerdynamic DT770 now. 

Installation of mini XLR jack complete

And finally we have the finished product featuring some cool colors, in this case rust with a black accent, terminated with a Switchcraft gold plated mini 3.5mm plug and a Neutrik / REAN mini XLR. Now these old Pros are ready for some stylish listening! 

I hope you enjoyed this post, please contact Zynsonix if you have a pair of Beyerdynamics (or any other headphone) that you'd like recabled or modified.

For more full-sized Beyer headphone mods, check out the Beyerdynamic T5p Recable and the DT880 Recable.

The Fine Print:

The above steps detailing the modification and re-cabling of a headphone are for entertainment purposes only and not to be performed under any circumstances. The owner of this blog and all associated parties can not / will not be held responsible if you attempt the process posted and cause physical harm to yourself, your surroundings or your property. Please keep this in mind.

Balancing the AKG K702 Headphone

The AKG K702 headphone is quite simply a black AKG K701 heaphone with a removable mini 3 pin cable. It's very nice to be able to remove the cable from a headphone with the click of a button, which is where the 3 pin mini-XLR comes into play. Switchcraft is well known for these connectors and offers them in a number of different pin configurations. Clicking the little black button on these connectors allows them to disconnect from the jack, so if a user runs over their cable with the wheel of a chair, desires a shorter or longer cable, or wants a cable of higher quality, it's very easy to swap a new cable in. Zynsonix offers replacement cables for the K702 among other headphones with removable cables if one is in the market.

With the existing 3 pin connector in the AKG K702, the two grounds for each channel are commonly connected. This won't work for a balanced connection to a balanced headphone amplifier where the grounds are run separately, so the existing three pin connector will be removed in favor of a 4 pin mini-XLR from Switchcraft.

In this post, a pair of K702s will be getting repaired with some high quality Eys 99.999% pure silver wiring (5Ns) in PTFE tubing. This particular pair of K702s had the previous jack accidentally ripped out (perhaps the headbanging got a bit too frenetic ;) ), but luckily everything inside is still in good working order. (I've found that with other AKGs, getting the existing jack out can be quite tricky, requiring a Dremel tool and quite a bit of patience). One will notice in the photo below, the white wire is the ground, in which both the left and right ground are commonly connected. In order to get inside the plastic shell, the grill needs to be rotated using a pair of jewelers screwdrivers, then two small screws are removed from underneath the grill.

AKG K702 opened

The first task would be to wire up the Switchcraft 4-pin mini XLR jack with silver wire, this would be replacing the existing wire within the headphone. Each piece was made a little longer than necessary and color coded for easy reference with electrical tape. The solder joints were covered with very small diameter heatshrink tubing to prevent the Teflon tubing from moving while the jack was being installed.

Silver wire soldered to Switchcraft mini 4 Pin jack

Now the jack could be slipped inside of the existing plastic shell. No dremeling or filing necessary is necessary when using a genuine Switchcraft jack. A strong adhesive does need to be used to keep the jack in place however. 

Switchcraft jack installed in the plastic shell

The stock wiring was removed at this point, a desoldering pump used to get off excess solder, and the new wires soldered in place. The solder points for the left driver are at the left-most and right-most points, and the solder points for the right driver travel along the headphone band, which are both closer to the center. Silver wiring was wired to the to the terminals and the plastic shell and grill were reinstalled. 

The plastic shell being reinstalled on the K702s

At this point, the matching silver cable could be built. Starting with a 4 pin mini XLR plug, the silver wires were soldered in place and small diameter heatshrink tubing was placed over the joints to prevent slippage of the Teflon tubing.  

4 Pin Mini XLR plug with wires soldered in place

The metal jack barrel was then slipped in place over the plastic piece housing the contacts. 

Metal barrel covering plastic housing

The wires were then braided in a litz formation and the strain relief clamped down on the wire tubing to prevent movement. 

Silver wire braided and strain relief clamped

The cable was then sleeved with soft black nylon multifilament. The remaining piece of the jack was filed to allow for the large diameter cable, then slipped over the sleeving and screwed to the metal barrel. A piece of adhesive black heatsrhink was added to act as an additional strain relief and help to keep the sleeving in place. 

4 Pin mini XLR completely installed

Cable sans mini connector

A Switchcraft mini connector could now be installed. You can see more details on a mini connector being installed in this previous post: Silver Plated Copper Mini to RCA Cable. The cable could now be clicked into place on the now repaired AKG K702. The mini connector is inherently non-balanced, but the user can now easily upgrade to a balanced cable when they are ready.

Completed cable on the AKG K702 headphones

UPDATE (6/14/12): The Quincy Jones Q702s are nearly identical, although the internal jack proved to be much more difficult to remove. The Q702s below were recabled using Zynsonix Ecs ultra pure ohno cast copper in Teflon.

Rewired with Zynsonix Ecs wire

These AKGs feature a fully balanced cable. 

Quincy Jones Q701 Balanced

I hope you found this post entertaining. Please be sure to contact Zynsonix if you'd like to take the music on your headphones to the next level.

The Fine Print:

The above steps detailing the repair and recabling of a headphone are for entertainment purposes only and not to be performed under any circumstances. The owner of this blog and all associated parties can not / will not be held responsible if you attempt the process posted and cause physical harm to yourself, your surroundings or your property. Please keep this in mind.