AKG D19c take apart

[martthie_08]

This came in the other day, a not-at-all working AKG D19c from a friend, who asked me to take a look at it. I get no resistance with my ohmmeter and decided to open up the mic housing and have a peek inside. It turns out these are rather fragile units and I'd like to ask for some advice before I mess up more than I can fix

I have managed to get the grille off by turning the three screws to the inside, thus revealing the capsule. The three screws near the Tuchel connector lets you pull the enclosure out of the shell.



It does not look all too bad in there, please click on the pics for higher res pics...





Now that the mic body assembly is out of the housing, what's the next step in taking this mic apart?



I can spot the blue wire coming from the Tuchel probably heading straight up to the capsule along with a fine magnet wire, I am afraid of tearing.

 

[rodabod]

Check continuity before the hum-buck coil at the termonals near the capsule. They will be covered by very delicate insulating cloth tube.

If the capsule is dead, remove the top screws which hold the diaphragm resonator on, and which also hold the diaphragm in place. Remove the resonator and now carefully lift the diaphragm. If you are lucky, the diaphragm will lift easily. If not, the diaphragm may either be glued, or just stuck to the paper spacers which the edge of the diaphragm sits in.

Anyway, when you lift the diaphragm, be careful not to snap the voice-coil wires as they are incredibly thin. With the diaphram lifted and possibly flipped over, inspect the voice coil and the wires leaving it for corrosion. If you are lucky, the wires leaving will have maybe a black spot and will be weakened or even snapped. You can graft on a new piece of very thin wire here if you have the skill. Otherwise, if the break is on the actual voice-coil, you'll have to unwind if you are very lucky. Usually only one end will unwind and you can remove afew turns.. You have to have to have the hands of a mic re-ribboner to manage this :razz: Only kidding. It is possible.

Good luck,

Roddy

 

[martthie_08]

I'm not 100% sure I understood, did you mean between the green and blue wires - if so, there is no continuity between these points!



I removed the six screws on top of the capsule and removed the resonator. To my eyes everything looks really clean for mic of this age, but there is a bump in the diaphragm, as you can see below!



Roddy, I am very very grateful for your help, thank you very much. I am trying to document this the best as possible for others that may run into a similar problem. As you can tell I'm new to (dynamic) mics, but I'm learning. :thumb:

cheers, Marten

 

[rodabod]

[quote author="martthie_08"]I'm not 100% sure I understood, did you mean between the green and blue wires - if so, there is no continuity between these points![/quote]

The hum-buck coil is in series with one leg of the capsule. I can't remember what the two wires attach to - I think one of the may attach to the hum-buck coil rather than the capsule. You want to measure the capsule alone in case the hum-buck coil is open-circuit. Actually, looking at the photo again, it looks like they do attach to the voice-coil wires, so that's ok to measure there.

I removed the six screws on top of the capsule and removed the resonator. To my eyes everything looks really clean for mic of this age, but there is a bump in the diaphragm, as you can see below!

Don't worry about the bump (although I do wonder where it came from...) You should be able to lift the diaphragm. Looking at your picture, lift it from teh opposite side from the green and blue wires and try to keep the green and blue wires close to it otherwise the wires will break!

 

[martthie_08]

ok, I'm moving on with this very slowly, I now have the capsule seperated from the mic body.



The diaphragm is glued between three layers of paper rings, I managed to lift it with a sharp knife. There are three screws under the last layer of paper, which is still glued to the metal underneath.



I have trouble understanding what the humbuck coil / where it is located - is it wired in series?

 

[ljupcopavlovski]

Hi..Its old thread but anyway I have similar  Akg d24 microphone which works but miss low end freq..
Low cut switch is broken ..I will post some pictures if anyone know hoe this switch work please help...I will attach some pictures (sorry its blurred--my crappy phone) ..On diagram I can see some glue,I don not know if this glue come from previous repair...

 

[ljupcopavlovski]

Another picture.

 

[ljupcopavlovski]

There is going broken switch..Inside I can not see any moving parts..

 

[ljupcopavlovski]

This is capsule and where is located glue on diagram...

 

[Sean Sweeney]

I'm fixing one of these now... one of the few people in the world that can do it... I can tell you that your "switch" is not a switch, but it is a bass port, which opens up the bottom of the mic and allows for greater bass response... you may not hear a lot of difference in your voice or tapping the thing... what you will hear is lower than 50hz response on drums and other miked instruments, because the air is allowed to move past the diaphragm... the same thing is true of a shure sm57, if you tape the sides, you will NOT get bass... your mic may have some GUNK stuck in the screen and fabric down the body of the mic, which is supposed to be able to breathe easily... that happens to some.

 

[snigglepit]

I have a question about the design of the D19. At the back of the capsule, there's a fairly thin brass tube that runs all the way down the mic. That seems to sit in a channel within a wider brass tube that is visible in the photos upthread, which in turn fits inside the shell of the mic.

My question is, does this second, wider brass tube have any part to play in the acoustic behaviour of the microphone? Or is it purely a structural element?