Detachable cable and wireless mod for the AKG K701 headphones
Tested with the new FiiO BTR3 (a review)
Exceptionally, I'm going to start the article with the end result. Below is a picture of my modified AKG K701 headphones with a FiiO BTR3 Bluetooth audio receiver clipped to the headband.
A long time ago I was planning on converting my AKG K701 headphones to have a detachable cable. Soon the Q701 was published having a detachable cable with a Mini XLR connector. It was followed by K702 and K712 and some others which all use the same connector. I hadn't used my headphones for a couple of years, but suddenly having found use for them I started thinking about the detachable cable mod again. I asked AKG and found out there was a repair shop in Sweden who sold AKG spare parts. They delivered to Finland the cover piece from Q701 with the Mini XLR connector. The correct part number, 2458M97040, could be found from AKG's service manuals.
Modding the headphones
To open up the K701 (and other 700 series headphones), bend a tool from a piece of metal and put it in one of the small holes in the cover piece - somewhere near where it says the model number is a good place. Then just pull it counterclockwise with pliers and remove the chrome cover. There are two screws. After opening them, the white cover piece may be removed. It is super tight, though. Using a knife helps.
As the K701 uses a fixed cable, the bottom part is also not compatible with the Mini XLR cover. I would recommend anyone else doing this mod to order the bottom spare part also. I had to carve quite a bit of plastic away to fit the new part.
I also had to carve the Mini XLR part quite a bit to make it fit. After the fit seemed good enough, I soldered the wires together and also put some heat-shrink tubing over everything, even the stock solder points. I hope this makes everything last pretty much forever. Interestingly, the yellow and red wires were swapped between the headphones and the Mini XLR connector.
Going wireless: a FiiO BTR3 review
Around the same time I did the detachable cable mod, I ordered the FiiO BTR3 Bluetooth audio receiver. It's a super-well made piece of cutting-edge Bluetooth technology, supporting every known codec currently available. These include aptX HD and LDAC.
I noticed the BTR3 with its integrated clip fits the K701 headband pretty well and decided to do a super short cable for connecting it there. I used the Sommercable Cicada SO-D14 cable and the Neutrik NTP3 RC-B connector, again both from Thomann. They feel pretty much indestructible and look quite nice. The result can be seen in the picture at the beginning of this article.
The FiiO BTR3 offers hands down the best sound quality I've ever heard from a wireless audio device. Its background is very clean and silent, there's no Bluetooth noise or hiss. Using the BTR3 with the KZ ZST Colorful brings out soundstage and power I've never heard from earphones - and without wires. The BTR3 is capable of driving even the AKG K701. I wouldn't say with ease, but capable nonetheless. Bass is always a bit troublesome if there's not enough power reserves, but when listening to Pat Metheny's Question and Answer album at night I couldn't help but stop at times to think the signal was actually transmitted via Bluetooth, and the sound was powered by the little sleek-looking device clipped on the headphones. Unless you need a very loud volume level, I'd say the BTR3 is capable of driving even demanding headphones to certain extent.
I've been mainly listening using the LDAC codec, but even with the old SBC codec things didn't sound nearly as bad as I'm used to expect from a Bluetooth audio device. The reception range also seemed to be quite a few meters and enough for most situations. I even had another Bluetooth device, a wireless mouse and a 2.4 GHz WiFi device transmitting a bit of data in the same room but the signal didn't seem to mind.
I've now used the BTR3 for a few battery cycles and I have nothing but good to say about it. Speaking of the battery, it seems to last really well also, we're talking about many hours here. Even if I don't have any technical measurement data to back up my short review, I'm going to go all Rolls-Royce and describe the performance of the FiiO BTR3 as "more than adequate". It does what it says it will, and it does it damn well.
Getting the LDAC codec to work on a desktop Linux
As I'm using pure ALSA without PulseAudio, I am using BlueALSA. The newest master versions support LDAC if you compile the codec library separately. The instructions can be found from the BlueALSA Wiki. The scripts and ALSA config I use for Bluetooth audio devices with Linux can be found in my dotfiles repository. I also wrote an extensive article about the use case to my blog.