AKG D12 NOS capsule - Does not sound right

[Tzurby]

I have a NOS D12 capsule (bought about 10 years ago, but never really used it). But it does not sound good.

Now I found the time to open it. When touching the membrane gently, there is a good hub (or throw?, my mother tongue is German) on one side. This is important for a good bass response, of course.

But on the other side, the membrane hardly moves down.

Here is a picture.

It does not looks as if the membrane has been warped (I have seen this on other capsules). But something gives it a downward pressure, so it can hardly move.

Could it be that the coils underneath have been clamped? It does not look like that, but I cannot preclude this.

Any recommendations for repair? I did not desolder it, as I shy away form this very delicate task. And this capsule still is NOS...

Thanks
Tzurby

 

[dmp]

I've have had a few D12/D20/D25 and they all can suffer from this issue where the voicecoil starts binding.
Usually they lose the low end.
I have successfully brought a few back to life but I also had one that I could not get healthy.
It is a difficult repair that requires a lot of care and precision.
If the slot for the voice coil actually has contamination in it, it is much more difficult. Mine have just been an alignment issue.
I think I just loosened the screws on one and shifted it slightly until it could move freely.
With yours, since it is not moving at all on one side, you might need to remove it. The voicecoil is very delicate and if it is bumped out of round you are done.

See this thread for pictures and description of the repair.
https://groupdiy.com/index.php?topic=33755.msg912531#msg912531

 

[beatnik]

It is not a good idea pressing the diaphragm with your fingers. You can damage the coil

Usually is possible to re align the coil by sweeping a tone in the capsule and adjusting for position where noise is minimum.

There are detailed instructions for this method if you search the forum

 

[panman]

The flutes are damaged on the left side .  At least two dents or folds are visible. The thing is, they are easy to fix, but only if you know how to do it, because otherwise you may just damage the diaphragm for good. Just one fold like that and the sound is lacking bass. By the way, you can press the diaphragm with your fingers, but here too, you need to know what you are doing.  Sorry, but it does not seem like you would know.

 

[chops]

I was hoping panman would chime in.  He fixed a D20 capsule (which was made extra difficult by a botched repair attempt) for me and really knows these well...

 

[David König]

If you have faulty D12 based mic (or generally ANY old vintage mic) you may sell it to me for reasonable price and I will fix it myself. Problem solved!