AKG D12 repair attempt...

[panman]

That washer is not from D12E. I cannot imagine what it was doing there.

 

[el-jon]

Appreciate all the replies, guys!

I removed the four screws from the bass chamber, but still stuck to the capsule... I bravely chickened out!
The mic measures about 210 ohm and has a great classic sound with deep bass, so I think I'll just leave it as is for now.
If nothing else I have somewhat familiarized myself with the mic (to the extent I can without becoming a pioneer).

 

[BOKIBeliGrad]

Pls. people, I think we should no longer take this post in this direction - noone will benefit from it. I hoped we stopped this before. Of course everyone is very welcome to try to repair anykind of microphone he/she want. Some might get lucky, some might not. I still insist: getting ANY D12 right could be a difficult task for some of us - and for some of us it won't. That's totally cool. And the ones that can't (me, @cyrano and a lot of other people) rely on @panman who really can fix ANY D12 and bring it into specs. As long as we're all happy in the end its cool! And of course: having NOS spare diaphragms would be a huge advantage. AFAIK panman doesn't have NOS diaphragms. He takes a heat air gun to bring them back to the correct shape. And this seems to me as a crazy piece of art.

So please let's get back to topic: to share ALL the best ideas to work on these mics to get them back to live!

God if he uses HEAT AIR GUN to bring diaphragms back into correct shape - that is a risky business and I dont think that I would dare to try that

 

[s2udio]

Just reloaded the images from my archive, (was a bit tense, thought they we on a dead ide drive)
But had a backup !!!!
Can't seem to remove the dead links (crosses) ho hum
Happy new year folks
https://groupdiy.com/threads/akg-d12-repair-attempt.33755/page-3

Quote
God if he uses HEAT AIR GUN to bring diaphragms back into correct shape - that is a risky business and I dont think that I would dare to try that
LOL

 

[GeorgeToledo]

God if he uses HEAT AIR GUN to bring diaphragms back into correct shape - that is a risky business and I dont think that I would dare to try that

It is possible he is using a die to reshape it, and keeping the time from hot to cool short. If so, it gets somewhat less risky.

Maybe he’s just blowing an air gun at it but I’m not sure that completely makes sense for getting it back to the correct shape all on its own, so there could be other aspects we just aren’t privy to.

 

[OneRoomStudio]

I used a heat gun to bring a different (much less rare and valuable) dynamic diaphragm back from the dead once, since it had "crinkles" in the folds. It wasn't actually that complex or delicate - a few careful passes of warm air and the capsule went back to its original shape. I didn't have to actually manipulate it at all (other than removing it from the mic to heat and then putting it back). There are plenty of ways this could go wrong (like melting the diaphragm if you heat it WAY too much)...but it wasn't anything all that difficult or magical. I know we want to keep punters from ruining valuable mics, but I don't like the way we act like some of this work is possible only by those ordained mythical figures who know the secrets of alchemy.

If you don't feel that you're up to the task, yes...please contact an experienced professional, but also let's not create more "magic mojo" mythology around these electromechanical tools.

 

[OneRoomStudio]

@s2udio, thanks for re-uploading the images! It makes it a bit easier to talk about these. One thing I have always wondered is if anyone knows the actual purpose of the three set-screws that surround the diaphragm. Since they are purposely made accessible when the diaphragm cover is on, they must be used for some kind of adjustment. I have gently messed with them a bit while fixing an old broken D12e, and they do impact the ability to tune the capsule for clear reproduction (and recording) of tones, but I don't know what they're actually doing. Does anyone here know what their specific purpose is? @panman?

 

[s2udio]

They are factory alignment screws for adjustment of the magnet gap, set on manufacture, aligned, then set (loctite).
The part was only supplied as a complete assembly, "system" as described in the spares doc.
If you actual force these in you will be causing even more problems !
Leave well alone IMHO, thats why I only cleaned the gap.

 

[OneRoomStudio]

They are factory alignment screws for adjustment of the magnet gap, set on manufacture, aligned, then set (loctite).
The part was only supplied as a complete assembly, "system" as described in the spares doc.
If you actual force these in you will be causing even more problems !
Leave well alone IMHO, thats why I only cleaned the gap.

If that's the case (that they are to be set once, during manufacture, and then never again), why did they make them accessible through the diaphragm cover? I understand that they may require a careful and judicious adjustment, and only when necessary, but clearly they can be adjusted even with the magnet gap not visible.

I'm hoping we can all educate each other about how these work and what the correct alignment procedure might be so that it's not lost to history. I worry that we too often people say things like "just don't touch that," and in another 10-20 years, no one will even know what they do. @panman won't live forever, and neither will you or I, so maybe we can help document this for future generations when they inevitably try to continue working on these mics that we leave behind.

 

[GeorgeToledo]

I used a heat gun to bring a different (much less rare and valuable) dynamic diaphragm back from the dead once, since it had "crinkles" in the folds. It wasn't actually that complex or delicate - a few careful passes of warm air and the capsule went back to its original shape. I didn't have to actually manipulate it at all (other than removing it from the mic to heat and then putting it back). There are plenty of ways this could go wrong (like melting the diaphragm if you heat it WAY too much)...but it wasn't anything all that difficult or magical. I know we want to keep punters from ruining valuable mics, but I don't like the way we act like some of this work is possible only by those ordained mythical figures who know the secrets of alchemy.

If you don't feel that you're up to the task, yes...please contact an experienced professional, but also let's not create more "magic mojo" mythology around these electromechanical tools.

If the plastic is heated for too long, and if it isn’t brought back to cool quickly but gradually, the membrane develops a very small hole pattern/dimpling on the surface (not all the way through the plastic). There is no magic mojo, just well vetted science that has been investigated by those who came before us, and which is possible to reconfirm.

When these capsules were originally formed the time from pressing it in a die at the correct temperature, to cooled while still in the die would usually be around a minute time, to keep the surface of the membrane in the best possible condition and base tension/rigidity as homogeneous as possible.

 

[OneRoomStudio]

If the plastic is heated for too long, and if it isn’t brought back to cool quickly, the membrane develops a very small hole pattern/dimpling on the surface (not all the way through the plastic). There is no magic mojo, just well vetted science that has been investigated by those who came before us, and which is possible to reconfirm.

When these capsules were originally formed the time from pressing it in a die at the correct temperature, to cooled while still in the die would usually be around a minute time, to keep the surface of the membrane in the best possible condition and base tension/rigidity as homogeneous as possible.

It would be fantastic if someone reproduced the die for the D12/D20/D25/D30 capsules, but I doubt that will happen. It seems that for the foreseeable future, we will be required to make repairs with the tools we have available.

 

[s2udio]

Other drum mics are available, and work well !
If you got one use it !
The AKG D12E is a very very good kick mic, but not for all situations, vintage relics cause myths !
Unless someone ! actualy has made replacement diaphram, then do best with what you have
I have moved on in life.
Just my 2cents.

 

[BOKIBeliGrad]

I have a D12E which was lying disassembled since some years in a cardbox. So i decided to try the sweep-signal-procedure. Tried three times, and still very thin. Then somewhere i read a guy who proposed to change position of the shimmer discs, means to take one disc from above the voicecoil and put it underneath the vc. I thougt strange, but gave it a try. So i plugged the mic in, took my headphones and when i grabbed the mic i already knew that something HUGE has happened. I won about 10 db's of gain and such a fat sound, i cannot believe. Now, my M88's and 441's sounds like crap compared to the D12E.
So far for my experience.
P.S. I can not really explain technically, why that happens, if someone has an explanation, i would be curious.

Hi if you are still around can you please explain this a bit better

 

[OneRoomStudio]

Hi if you are still around can you please explain this a bit better

Are you asking him to explain the procedure? If so, that's detailed throughout this thread, especially the first few pages. Go back and read the whole thing.

If you're asking why it works, it's because over time, magnetic filings and oxide prevent the free movement of the diaphragm and coil, which causes the loss of low-end. In some cases, it's possible to realign the coil in the magnetic gap simply by moving the diaphragm around and listening for a clear (undistorted) singal from the capsule while it's wired up as a small speaker. In other cases, you have to take the capsule apart and clean the oxide and magnetic filings off before aligning the diaphragm/coil in order to get it to move freely.

 

[panman]

@s2udio, thanks for re-uploading the images! It makes it a bit easier to talk about these. One thing I have always wondered is if anyone knows the actual purpose of the three set-screws that surround the diaphragm. Since they are purposely made accessible when the diaphragm cover is on, they must be used for some kind of adjustment. I have gently messed with them a bit while fixing an old broken D12e, and they do impact the ability to tune the capsule for clear reproduction (and recording) of tones, but I don't know what they're actually doing. Does anyone here know what their specific purpose is? @panman?
View attachment 142413

Those screws are there just to align the paper-shims and the ring locking the diaphragm in tune. They do not adjust anything. The bigger holes on the shims and the ring fit exactly on those screws.

 

[OneRoomStudio]

Those screws are there just to align the paper-shims and the ring locking the diaphragm in tune. They do not adjust anything. The bigger holes on the shims and the ring fit exactly on those screws.

Thank you! I'm guessing the effect I was hearing was just the threads of the screws slightly moving the paper shims as I rotated them. Good to know that they don't have an actual adjustment purpose.

 

[s2udio]

Those screws are there just to align the paper-shims and the ring locking the diaphragm in tune. They do not adjust anything. The bigger holes on the shims and the ring fit exactly on those screws.

yes correct
I thought the reference was to the 3 screws attaching the ring to the body outside the top assembly apologies

 

[Whoops]

It would be fantastic if someone reproduced the die for the D12/D20/D25/D30 capsules, but I doubt that will happen. It seems that for the foreseeable future, we will be required to make repairs with the tools we have available.

I guess you are talking about reproducing a die for the diaphragm and not the "capsules".
If that's what you meant, there were some talks about it in the past, I don't remember if it was in this thread or another one around here.

There's many factories in China that would reproducing a die and make quality diaphragm replacements for the D12 family of mics, but for that to happen they would need an order of huge quantities, and repairing D12 is a very very small niche,
so it's not cost efficient for them to go through that process to sell in the end just 20 or 50 units.

But if someone has direct contact with factories that manufacture Dynamic moving coil microphones it would be nice to ask them about the possibility of doing this.
Anyone?

Other option might be in the future when a company in China decides to clone the D12 microphone and sell it.
If they clone at least the diaphragm very well, then there will be a source for it.

But they are more focused on cloning Neumann microphones, which are expensive mics, so they have a bigger profit margin.
And also cloning current Shure and Sennheiser mics because are very well know and have a lot of demand, so although the profit margin is smaller they sell much more units.