AKG CK12 Teflon Repair and surprise

Hi,
I would like to share a very instructive story.
I've recently repaired two Teflon Ck12.

Both was bad sounding, in par with their reputation.

After a complete dismantle, i found that a very important part was completely destroyed (aging).

The spacing foams under the diaphragm were rotten, thus the factory gap between teflon and backplates (thus also between membranes and backplates) was unreliable...
You can see the foam residuals in the upper right side of the picture...
So i've cut some spare ring foams and after a good cleaning, i've rebuilt the capsules.
After some adjustments (checking the polar patterns) on the position of the screwed diaphragm, i as very surprised with the result.

There was a massive improvement on the sound quality, and matching sides...

i would say a little darker than Brass CK12 , but not that far in terms of overall quality...

Regards
Fred

http://www.saturn-sound.com/Curio's/akg's%202072%20z%200009%20capsule.htm

Awesome. Thanks.

I have also had success in the past using an insulated spring wire and winding a spring that keeps pocket size constant.  Result was nice and I agree, not bright but certainly not horrible either

Aah, very interesting development indeed - can explain some mysterious changes over time that seem unrelated to anything seen by the naked eye.

How hard is is to take apart without destroying the membranes? Method?

/Jakob E.

gyraf said:

Aah, very interesting development indeed - can explain some mysterious changes over time that seem unrelated to anything seen by the naked eye.

How hard is is to take apart without destroying the membranes? Method?

/Jakob E.

Click to expand...

Not too difficult at all.  I use a tool that i made .  I turned a pei e of brass to the right size.  It needs to have a really thin sharp wall.  Then mill away half of it so it looks like a half moon.  The wall can only be about 300um in order to fit inbetween the ring and teflon wall.  Push in gently and lever the membrane out.  I’m sure a small screw driver could do it also but it will bruise the teflon due to the fulcrum load on the teflon.

you can also  unclip the diaphragm by pulling it  gently with a clamp, thanks to the front pin...
it comes easily
then , you have to unscrew  the removable half of "Teflon" capsule frame
Done...
the more i use this capsule now, the more i like it, especially in front of a guitar amp, but also with my voice...
i recommend to all the Teflon ck12 owners, to repair them if they noticed a sound  degradation...

Hello, very interesting, thanks.
Is there some more information about what years / capsule types might be affected ? Or is it virtually all AKG Teflon capsules.

AboveAndBelow said:

Hello, very interesting, thanks.
Is there some more information about what years / capsule types might be affected ? Or is it virtually all AKG Teflon capsules.

Click to expand...

As near all the nylon CK12 I fixed were affected (5 on 7 capsules), on one or both sides , chances are high..
BTW I really like the sound of these once fixed...
Don't hesitate to scrape all the spacing material even if it's partially affected

granger.frederic said:

BTW I really like the sound of these once fixed...

Click to expand...

Very hypothetical question, but would you consider the fixed version worthy of cloning?

What kind of foam did you use for the rings? Do you have any specs?
Thanks!

why on earth they thought this type of foam was the right way to set this gap precisely long term is beyond me. and having it constantly under pressure against the fit is absurd. admittedly i assumed people were joking or being overly mean to the teflon ck12's design back when i first started researching capsules, but taking one apart it really is a real head-scratcher.

soliloqueen said:

why on earth they thought this type of foam was the right way to set this gap precisely long term is beyond me. and having it constantly under pressure against the fit is absurd. admittedly i assumed people were joking or being overly mean to the teflon ck12's design back when i first started researching capsules, but taking one apart it really is a real head-scratcher.

Click to expand...

medium density foam, a bit thicker than the original hard foam (measure before cleaning)

not critical as the right spacing is defined by the outer nylon structure , once the diaphragm re-clipped...

if you do it well the capacitances are almost identical on both sides

the diaphragm unclip easily most the time, do not damage the outer nylon edges...

don't forget to clean everything, re-mount the spacer between the diaphragm and backplate, and test / adjust the capsule, once fixed, for best rear rejection in cardio.

you can add or remove small quantities of varnish on the inner small center metal grid, and adjust the screwing pressure of the removable capsule side , to fine tune it..

In fact the fix works surprisingly well most of the time
good luck...

cheers
Fred