AKG CK12 Teflon Repair and surprise

[granger.frederic]

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

 

[mics]

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

 

[gyraf]

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.

 

[mics]

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.

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.

 

[granger.frederic]

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...

 

[AboveAndBelow]

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.

 

[granger.frederic]

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.

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

 

[ElSmurf]

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

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

 

[bremusound]

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

 

[soliloqueen]

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.

 

[granger.frederic]

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.

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

 

[VanguardAudioLabs]

Risking resurrecting an old thread, but took apart two damaged Teflon capsules today.

The one on the LEFT is from a C414EB P48. The capsule degradation was such that the bits of foam had slipped through the holes in the backplate and were creating mulitple "tents" underneath the diaphragm. By gently shaking the capsule, i could release even more of the foam and create more tents.

The one on the RIGHT is from a C414B-ULS TLii - technically a different "model" of capsule - the 2072 Z 0009, which has the dimpled diaphragm ring and a different internal acoustic network. The foam is glued to the backplate.

Measurements of the newer foam ring taken with digital calipers for those that need replacement -
OD 29mm
ID 25.5mm
Thickness 1.15mm

I'll probably cut a bunch of these on our fiber laser for future repairs.

I'll also have to do some investigative work as i repair mics and see when they changed over to the newer foam. according to saturn sound (http://www.saturn-sound.com/Curio's/akg's 2072 z 0005 capsule.htm) the Z0001 thru Z0005 capsules were allegedly the same, but i assume they changed the foam material at some point on them as well.

 

[Double G]

Seeing as the results of modifying the original nylon CK12 brought it subtly closer to the brass version I wanted to reply with asking what the TLII capsule might sound like, because to my ears the TLII sounds remarkably close to my brass 414EB. But now I see you have done it.

I would be very interested in knowing how it sounds once you're finished.

 

[VanguardAudioLabs]

Seeing as the results of modifying the original nylon CK12 brought it subtly closer to the brass version I wanted to reply with asking what the TLII capsule might sound like, because to my ears the TLII sounds remarkably close to my brass 414EB. But now I see you have done it.

I would be very interested in knowing how it sounds once you're finished.

The TLii already had this foam which indicates to me that at some point AKG rectified their mistake

 

[GeorgeToledo]

The TLII was their attempt to specifically match the sound of a capsule in a mic owned by Peter Wolf, the producer (not the singer).

 

[Double G]

The TLii already had this foam which indicates to me that at some point AKG rectified their mistake

Oh ok. So the modification is already part of the capsule design.

The TLII was their attempt to specifically match the sound of a capsule in a mic owned by Peter Wolf, the producer (not the singer).

Yes. It was a C12 Klaus H. worked on.

Now, I don't know if this requires a separate thread but I had to send my EB to Richard Land because it was way too thin sounding when I got it. He brought it back to life.

He was telling me that it was AKG's policy at the time to use the TLII capsule whenever a brass capsule 414 was sent in for repair and needed a new capsule.

That got me wondering what the EB's circuitry might do to the sound of the capsule.

I'm aware that the circuitry isn't anything special but to me it doesn't sound like it wouldn't need much of a shift. That and it would be nice if it might smooth out some of the transients because the TLII tends to overload my preamp a lot easier than the brass and nylon EB.

 

[VanguardAudioLabs]

He was telling me that it was AKG's policy at the time to use the TLII capsule whenever a brass capsule 414 was sent in for repair and needed a new capsule.

That is correct. i recently worked on a C24 gen1 that had Teflon capsules in it from an AKG repair in which the brass capsules were found to be the issue.

That got me wondering what the EB's circuitry might do to the sound of the capsule.

I will say that capsule being equal, i prefer the C414EB-P48 version to the C414EB. P48 is underrated; i think people prize the EB because it was the last version to use the brass CK12 (although not all of them did; I think they transitioned to the Teflon CK12 sometime during the EB.)

Although the pattern switch on the P48 is an odd component that they only ever used for the P48.

Oh ok. So the modification is already part of the capsule design.

That's correct. I think at some point AKG realized the foam they used early on was degrading. I'm curious to know which version of the standard Teflon capsule (0001 thru 0005, not the TLii which is 0009) they switched over to the new foam as well.

I ordered some 1mm adhesive foam sheets and they'll go on the laser cutter next week for future repairs.

 

[DFischer]

So to confirm, the TLII 2072 Z 0009 capsules have foam springs that do not degrade over time? I have a TLII that doesn't seem to sound quite as good as it used to, but I can't really say if the mic changed or if I did.

 

[VanguardAudioLabs]

So to confirm, the TLII 2072 Z 0009 capsules have foam springs that do not degrade over time? I have a TLII that doesn't seem to sound quite as good as it used to, but I can't really say if the mic changed or if I did.

The one i opened has a better foam spring in it. It's certainly newer and not the same weird orange/yellow color of the old disintegrating foam.

There is the possibility someone serviced this previously, or that they changed the foam sometime in the middle of the TLii (00009) run. I'd ask AKG but all those dudes are gone. maybe i can ask my friends at Austrian Audio and they'll remember.

 

[DFischer]

I purchased it new in the mid-late 90's, so I know it hasn't been serviced. Seems like it doesn't involve invasive surgery to take a look though. I'll put it on my list to take a peek.