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Driver for mid production K1000


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Well the saga continues. Miguel had asked me to recable the 2nd K1000 while I already had them disassembled, which I was more than happy to oblige. As part of normal procedure I checked for continuity after soldering one side of the cable and there was, what, nothing? That can't be right, so I checked it right at the solder posts, still nothing. Okay, says I, maybe this is just one of those rare but not unheard of occasions where the voice coil wire connection fails during the process of removing and reattaching the PCB. I remove the blue goop and resolder those wires, and there's still not a bit of continuity.

Pushing on the driver to bounce it up and down while I stared at it in thought and frustration, I noticed something odd, very odd. Specifically, it didn't bounce up and down as I pushed on it, instead of made a scratchy noise and resisted movement. Well that's certainly unusual. Looking the driver all over very closely from all angles, when I pushed it outwards some from the back I noticed a small sliver of metal in the gap the voice coil sits in!


Looks like I was wrong about the primary cause of the buzzing after all, but the driver still does not move freely and the damage on the voice coil wire still needs to be located. With that, there was only one choice: complete disassembly of the driver. I'd not dared to go this far on a K1000 before as there was never a need to, so it was uncertain how easily it would let me proceed. With all the delicacy and caution I could muster I set to work on it... and it came apart easier than pretty much any driver I've worked on before.



With the rest of the bizarre metal debris removed, the diaphragm finally moves freely as it should. I did not notice any readily obvious damage on the voice coil, which is good that it's not totally screwed up, but I still have to continue examining it to track down where the actual break is. Hopefully it isn't on the voice coil proper and instead is somewhere on the two leads that go to the solder posts.

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Dang, it's kind of like shrapnel from a grenade lodged in there. May the Restorer of all that is vintage-holy AKG perform a miracle on this driver. Btw sorry for being daft and/or blind, but where exactly is the voice coil in the third pic?

Looks to be fully removed, so not in that pic.

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That looks suspiciously like metal shavings caused from drilling into sheet metal. How the hell they got into a K1000 driver is beyond me. I suspect this guy had his screens off like some people rave about, and was DIYing something much too close to the headphones.

Miguel is damned lucky that he chose you to fix them! You da man Fitz!

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The screens were still glued in place, so I don't think they were ever removed before now. Regardless, it wouldn't be difficult for something to get into the back of the driver even with the screens on, if one were careless enough. Considering how nasty these are (I still haven't gotten the diaphragm totally clean, there's some stuff on it that resembles spraypaint overspray...), it's certainly within the realm of possibility.

Edited by Fitz
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Well I went to go look at those metal bits again to try to identify them... they're both about the same length, width, thickness, and with square ends, So I don't think it's metal shavings from drilling. That's not the real point though, I was also looking over the driver again just to examine its construction and something odd caught my eye, couldn't be sure from squinting, so I grabbed a loupe and looked at it closer. When I twisted the wires on the front a certain way, part of it stuck out a little in the middle... it was the break in the voice coil wire! And it's on the part that's in the front of the driver relatively easy to repair, not on the voice coil itself! It also looks like it got pulled on a bit where it penetrates through the diaphragm to actually go and become the voice coil. So I'm guessing the metal bits had caught on it at some point and pulled it tighter than normal, I go to recable it and happen to flex the little wire/string bundle on the front just the right way... SNAP, that one wire breaks.

I still need to perform the repair to make sure there's nothing else wrong, but this would make sense with how things have developed thus far, so I feel good about it.

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Fitz, you should be a brain surgeon! The skill and "cojones" you are showing is beyond belief. As stated by a far more eloquent person than I, the fact is I am damn lucky you are working on both of my K1000. Most anyone else would have given up and way sooner. Yes, I am very thankful for the work you are doing.

BTW, I looked at one of your pictures and is there another piece of metal stock in the driver? I have copied the picture you took and I have placed a pink arrow to the "stuff". Oh, and you must have eyes like a tiger to see all of the small stuff inside the driver.


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Heh, I appreciate the kind words Miguel, but I enjoy working on things for other people far, far more than for myself or some random guy hiring me to do it. The piece of metal in the picture you've highlighted is the second bit of metal debris I mentioned to you before. I took the picture before taking it out so people could see where it actually was.

I also went and twisted the front wires a little more and was able to get the break to stick out from the rest of the bundle. Take a look at this pic, keeping in mind these wires are about the thickness of a hair:


I do wish I had a spool of magnet wire as ultra friggin small as is used on headphones though, I only have really friggin small magnet wire. :P

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Oh boy, if I'm gonna take an after pic I'll have to do it much neater than usual, since what looks fine to the naked eye might look awful with a super close-up pic. The process itself isn't that bad if one is comfortable working with such small wire in the first place, it's pretty much a very scaled down version of soldering two normal wires together. I'll need to tin about 1mm of the end of the wire that goes to the voice coil, and also do the same on a new piece of magnet wire to go the rest of the way (there's not enough slack to reuse the existing wire). The tricky part is getting both wires positioned so they overlap slightly and then soldering them together; generally this is a process of trial and error, and they often end up slightly crossed rather than perfectly parallel. After they're soldered and I've reinstalled the diaphragm into the main housing, I'll wrap the new wire the rest of the way around the string, and solder it and the undamaged wire back down to the posts at the PCB.

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Here's a quick pic I snapped after soldering on the new extension:


Didn't come out perfect, but the original wire wraps around the new one slightly so it'll be fine from a functional standpoint. I put a tiny dab of glue on the solder joint to secure it to itself and the string so it won't get flexed when the driver is moving, which I'll wait to fully dry before finishing the repair.

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