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General Discussions => The Lab => Topic started by: SSLtech on May 26, 2009, 02:09:44 PM

Title: AKG D12 repair attempt...
Post by: SSLtech on May 26, 2009, 02:09:44 PM
So I've got this D12 which has no low end. (yeah... the old story!)

The acoustic chamber seems to be clear, and I notice that at some time it may have been dropped, since the one of the four brackets to which the suspension 'leaf-springs' attach has been bent slightly and was pressing against the diaphragm surround.

-So I bent back the bracket, but there's still no low end.

More investigation required...

I notice that the two ends of the voice coil wire are 'sleeved' and joined -VERY delicately- to the wires which run to the 'transformer' around the perimeter, but if I wanted to investigate the 'centering' of the diaphragm for example, What shoudl my next step be?

-Do I need to (CAREFULLY!) desolder the voice coil ends?

And then which screws do what? There appear to be three recessed screws (one every 120°) at about 2, 6 and 10 o'clock... but then there are also six screws which sit proud of the surface, at about 12, 2, 4, 6, 8 and 10 o'clock also...

I thought that Rod and Zebra50 had some D12 repair suggestions somewhere, but I can't find anything. -Would this be worth photographing in case it helps anyone?

Keith
Title: Re: AKG D12 repair attempt...
Post by: rodabod on May 26, 2009, 03:20:54 PM
There ae probably mentions of this here and on R/E/P, but it's bee a while since I disassembled one.

The diaphragm is attached much the same way as the D19 (also fail when they get old), but I can't remember seeing any recessed screws.I do have pictures of D19 repair, but they were pretty obscene, including unwinding a broken coil and a voice-coil transplant....

There should be (depending on the year) some paper shims which set the clearance of the diaphragm from the magnet. The diaphragm uis sandwiched between a number, but these can be rearranged to vary the clearance which may need to be increased. Thsi can also in some cases be achieved by just re-seating the diapgragm and not tightening the pressure ring too tightly. You need to watch out for voice-coil rub (which may be what is causing bass loss) by trying by eye to align the diaphragm as centrally as possible. There is another method of doing this by trial and error which is to use a sine generator and excite the diaphragm whilst listening for a clean tone. Sine being the best choice as extra harmonics are most noticeable.

Regarding removing the voice-coils from the wires which run to the socket or transformer, it's up to you. I usually leave them on and flip the diaphragm over carefully, but it's a risky business. Soldering isn't much fine as the wire melts. To solder, tin both wires (this removes the enamel from the voice-coil wire) without melting, then spiral a few mm of the voice-coil wire onto the thicker wire.

Then have a drink.
Title: Re: AKG D12 repair attempt...
Post by: MagnetoSound on May 26, 2009, 03:46:58 PM

There is another method of doing this by trial and error which is to use a sine generator and excite the diaphragm whilst listening for a clean tone. Sine being the best choice as extra harmonics are most noticeable.


Good call, I would try this method first. I don't mess with the voicecoil wires unless I really have to. Somewhere around 5kHz works well as you can hear it best from a small driver. You can monitor the waveform on your scope at the same time.

Did you search PSW? Esa (panman) might have some tips.


Quote

Then have a drink.


Best advice yet.  ;D


EDIT: Of course - as  Keith says lower down, you sweep the freq of the generator to check for trouble spots, you don't just test at one single tone. Duh!
Title: Re: AKG D12 repair attempt...
Post by: Rob Flinn on May 26, 2009, 04:01:23 PM
I had a similar problem D12.   After some investigation I just bought a new capsule from AKG in Austria.  They still make them (or did about 3 years ago), but I think they only do a batch every so often.  It was only about 130 euros inc shipping.
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on May 26, 2009, 04:11:10 PM
I think they're not doing so any more... certainly AKG USA say not.

-But I've taken the suggestion to hook it to a generator, and if I sweep a -10dBv (15Ω source Z) sine wave tone, I get a distinct 'buzz' at around 1.5kHz...

So if I wanted to 'shuffle' the diaphragm round a little, is it the THREE screws, or the whole six, which I should loosen?

-Much obliged for the ideas so far... the sig. genny idea is brilliant lateral thinking, -thanks!

Keith
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on May 26, 2009, 04:26:05 PM
Ah... there's a pic in JJ's response to this post form Oliver, which shows the three 'recessed' screws:

http://recforums.prosoundweb.com/index.php/mv/msg/13463/188515/2172/

I'll carefully have a further look at mine.

Cheers!

Keith
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on May 26, 2009, 05:14:54 PM
Quote
Thsi can also in some cases be achieved by just re-seating the diaphragm and not tightening the pressure ring too tightly.

May the Lord bless you, Roddy! This is precisely what worked for me.

Now I suspect I may need to add some nail-polish to the screws to keep everything in place. (And possibly at a couple of spots on the ring to prevent it too from shifting?)

One thing: the three 'recessed' screw holes are in fact CLEAR holes which merely allow access to the screws beneath. These are NOT associated with the diaphragm position in any way.

So I kept the tone at the 'buzzy' frequency, (approx. 1.5kHz in this particular case) and loosened off the six tiny screws, including the two which hold on the wire end "sleeves", until they were all fully loose by about a quarter-turn. Then using a thumb and forefinger, I gently 'slid' the diaphragm around on the face, listening to the 'sharpness' of the buzz. After tuning for minimum 'fizz', I increased the amplitude slightly and swept up and down. I found a slight 'fizz' at the low end (about 200Hz) and slipped the diaphragm around some more. I noticed however that the 'evenness of response' of the diaphragm 'singing' to the oscillator was already rather better, and this gave me some great encouragement.

So finally I took it over to the test preamp and... Hallelujah!!! Deep, stentorian bass!

[sniff] -I love this place!!! [sniff]

Keith
Title: Re: AKG D12 repair attempt...
Post by: Rob Flinn on May 27, 2009, 04:48:42 AM
I think they're not doing so any more... certainly AKG USA say not.

Keith

You need to contact Karl Peschel at AKG in Austria, he is the only one who really know what's going on with AKG spares, & is extremely helpful.
Title: Re: AKG D12 repair attempt...
Post by: Sredna on May 27, 2009, 07:48:44 AM
Hi!

I got the same problem with a D112.

I opened it up and found no ovious problems, cables, resistance and membrane looks ok..

What are there similarities/differences between D12 & D112?

Thanks,

Anders
Title: Re: AKG D12 repair attempt...
Post by: craptical on May 27, 2009, 09:06:40 AM
Suddenly it feels good to have kept the old capsules from our D12´s :)
Title: Re: AKG D12 repair attempt...
Post by: rodabod on May 27, 2009, 10:16:49 AM
What are there similarities/differences between D12 & D112?

Different mics; the D12 has a modular capsule. I believe the D112 will have a glued/sealed diaphragm.
Title: Re: AKG D12 repair attempt...
Post by: rodabod on May 27, 2009, 10:18:18 AM
Oh, and Keith, I'm glad you managed to sort it. It's nice to get a result from sharing a bit of info here.
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on May 27, 2009, 11:57:12 AM
Quote
It's nice to get a result from sharing a bit of info here.

No kidding, 'Rocking Rod'!

I do so little rock recording with my gear these days and I'd largely lost interest in fixing the D12, but last weekend a classical engineer whom I respect very much indeed dug his out to use as a spot mic on a bass drum during a Brass Band recording session... and I almost kicked myself!!! The respect which he afforded the mic was fully vindicated when he brought up the fader!!!

It inspired me to 'grasp the nettle firmly' and dig into mine... and thanks to your welcome ministrations, it's been a true success!

Thanks again!

Keith
Title: Re: AKG D12 repair attempt...
Post by: Rob Flinn on May 27, 2009, 03:46:31 PM
I love my D12.  That on kick drum with a single D19 overhead is a favourite set up for some recordings.

A friend has a D30, & that is fantastic sounding on kick.  It has 2 D12 capsules in it , with controls to change pattern & response.
Title: Re: AKG D12 repair attempt...
Post by: strangeandbouncy on May 27, 2009, 04:04:01 PM
Hi,


  were she still with us, I'd happily sell my Granny for a D30!!! Long time since I had the pleasure. Awe inspiring on Bass Cabs too . . .



    Kindest regards,


     ANdyP
Title: Re: AKG D12 repair attempt...
Post by: strangeandbouncy on May 27, 2009, 04:08:03 PM
Hi Rob,


  I think D30 has 2 D19 capsules in it. I could be wrong . . .



   Kindest regards,



     ANdyP
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on May 27, 2009, 04:45:57 PM
I'd happily sell my Granny... ...Long time since I had the pleasure.

Wow!

-THAT's no reason to sell her!

 ;D
Title: Re: AKG D12 repair attempt...
Post by: Rob Flinn on May 27, 2009, 04:51:10 PM
Hi Rob,
I think D30 has 2 D19 capsules in it. I could be wrong . . .
Kindest regards,
ANdyP

Actually it looks more like a D12 & a D19  http://www.pomaudiodesign.com/page3/files/page3-1006-full.html
Title: Re: AKG D12 repair attempt...
Post by: rodabod on May 27, 2009, 07:15:32 PM
Actually it looks more like a D12 & a D19  http://www.pomaudiodesign.com/page3/files/page3-1006-full.html

From that image, I'd guess two D12 capsules, sans bass chambers. D12 + D19 would be a little odd.
Title: Re: AKG D12 repair attempt...
Post by: eskimo on May 27, 2009, 07:27:33 PM
Speaking of D19, I'm trying to get mine working...

I suspect those hair thin coil wires to be the problem. Any ideas or suggestions?
Title: Re: AKG D12 repair attempt...
Post by: strangeandbouncy on May 27, 2009, 07:28:36 PM
I saw one(D30) with it's cover of a cople of months ago, and I am sure the two capsules were the same . . .
Title: Re: AKG D12 repair attempt...
Post by: eskimo on May 27, 2009, 07:36:47 PM
Ok, I just realized how the d19 is constructed and how royally f**ked I really am.  ;D
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on May 27, 2009, 07:40:40 PM
Nice thread, thanks for the info-sharing !  :)
Now let's hope the generator-trick works for my bass-shy D12 as well.

Apart from that and assuming that trick does the trick, anybody a suggestion how to cleanup the dirty inside of the mesh-cage ? (see attached pic)

(I need to fix the surround as well but got already a suggestion for that.)

Bye,

  Peter
Title: Re: AKG D12 repair attempt...
Post by: abbey road d enfer on May 28, 2009, 01:30:58 AM
Apart from that and assuming that trick does the trick, anybody a suggestion how to cleanup the dirty inside of the mesh-cage ? (see attached pic)

Bye,

  Peter
Since it's constituted mainly of iron oxide (commonly referred to as rust), use a phosphoric acid-based rust cleaner. Just google for it, it is available from most car and diy shops. Don't be afraid by the concept of using an acid product on your cherished microphone. Phosphoric acid dissolves rust and creates a very thin protective layer of iron phosphate. Apply product with a brush, let it react for 15 minutes, rinse and repeat if necessary. Most suppliers of this type of product offer a passivating product. The use of such a product is justified only for large parts that cannot be rinsed properly. For your mic basket, rinsing under the tap for 30 seconds is enough to passivate.
Title: Re: AKG D12 repair attempt...
Post by: MagnetoSound on May 28, 2009, 02:09:22 AM

You can also try Alka-Seltzer: http://www.videojug.com/film/how-to-remove-rust-from-small-objects

... or electrolysis: http://www.videojug.com/film/how-to-remove-rust


BTW, I don't expect that any of these methods are likely to save the wind-resistant flock lining of your grille - but let us know.
Title: Re: AKG D12 repair attempt...
Post by: rodabod on May 28, 2009, 08:13:40 AM
Speaking of D19, I'm trying to get mine working...

I suspect those hair thin coil wires to be the problem. Any ideas or suggestions?

Start by measuring coil continuity at the socket (there isn't a transformer in the single-impedance models).
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on May 28, 2009, 10:18:22 AM
Thanks all for the tips !

BTW, I don't expect that any of these methods are likely to save the wind-resistant flock lining of your grille - but let us know.
The funny thing is, the grille looks decent on the outside, the uglyness is just on the inside. But it gives the impression that it sort of congests the small openings, not sure.

Assuming that the flock will indeed disappear, how important would it be for a bass-mic that will be used indoors 99% of the time ?  It will see some moving air of course, since I'm after that stentorian bass as well  ;)

Bye,

  Peter
Title: Re: AKG D12 repair attempt...
Post by: MagnetoSound on May 28, 2009, 03:59:00 PM

Assuming that the flock will indeed disappear, how important would it be for a bass-mic that will be used indoors 99% of the time ?


LOL, I asked myself that as I was posting earlier.

Dunno! I doubt it will be a problem on bass guitar, on bass drum I guess it might, if used outside and in front of the drum where the wind is strong ... close to the head, perhaps not.
Title: Re: AKG D12 repair attempt...
Post by: EmRR on May 28, 2009, 07:05:40 PM
good work gentlemen; another set of techniques for the files. 
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on May 29, 2009, 12:06:58 PM

On the topic of D12... D12E.... has anyone ever seen a clone/copy that has
the big monster-capsule-engine-motor-capzilla inside ?

I read about clones that look like a real one from the outside,
but simply have something else inside.

There happens to be a certain 'Electric Sound' copy for sale here, but can't imagine
the clonists took the trouble to go Jules Verne and all.
I know I should pass on this, but OK...   

I can obviously test it, but he won't let me open it I expect. If it has the sound
then it has the sound, but that'd require better test-possibilities than doing a bit
of pfah-pfah over there.


Thanks,

  Peter
Title: Re: AKG D12 repair attempt...
Post by: EmRR on May 29, 2009, 12:38:08 PM
I've also seen at least one D12 body with a ribbon motor hacked into it.   Supposedly came out of USSR. 
Title: Re: AKG D12 repair attempt...
Post by: rodabod on May 29, 2009, 01:55:48 PM
There is one Italian company that made a clone. It wouldn't probably trust it to be similar though.
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on May 29, 2009, 06:36:02 PM
Can't imagine the 'local copy' has the Big Thing inside...

Hmm, if the price was lower I might go for it to get a new unbroken surround  ;)

Bye,

  Peter
Title: Re: AKG D12 repair attempt...
Post by: s2udio on June 17, 2009, 01:03:38 PM
-Would this be worth photographing in case it helps anyone?

Keith
Oh yes please.............!!!
unless i missed the boat ?
Just bagged one on evil bay( for a few peanuts !) with said symtoms,and a healthy reading of the voice coil
........275 ohms ?
Attempt at repair to be made using Roddys method.........shortly
ps Will photo the process,and post results (if sucessfull.........unless of course Keith you already have  ;))
any more tips ?
Title: Re: AKG D12 repair attempt...
Post by: biasply on June 26, 2009, 11:56:58 AM
Really glad I found this thread (Thanks to Roddy)....
Have an old Echolette D12 that I thought needed a new capsule due to tinniness, but now I have an option to try....
Thanks!! this forum is simply amazing...
Steve.
Title: Re: AKG D12 repair attempt...
Post by: biasply on June 26, 2009, 12:22:27 PM
Okay so I got the thing opened and the 6 screws loosened, but I can't get the diaphragm to move around the way it sounds like it should?  Also the ring held by the 6 screws is still quite fixed.... any thoughts?

Steve.
Title: Re: AKG D12 repair attempt...
Post by: Martin B. Kantola on June 26, 2009, 07:15:53 PM
So reading this thread I remembered having a bass-less D12 motor somewhere. And yesterday there was suddenly a little time to hook it up to the trusty old and green B&K all-tube tone generator. The problem was very obvious, terrible buzzing especially at any lower frequency sounds. So I kept the frequency at around 100Hz at a reasonable level, and started loosening  the screws that hold the diaphragm. Didn't take me too long to find a position where the buzz was minimal, but the trick was to get all screws tightened while maintaining that position. The gap seems pretty narrow. Used a bit of drum head tuning method, plugged in the mike and SUCCESS! Although I need to test it on a real kick too, but happy happy joy joy!

My sincere thanks, have probably had this nonworking microphone for 20 years...!

 ;D

Martin
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on June 27, 2009, 11:58:00 AM
MARTIN!

-Good to 'see' you again!

I was thinking about our mutual acquaintance over the last day or two... (of course). -I hope all is well.

...and I'm glad that my little 'voyage of discovery' has benefited you also! -I think this should be made a 'sticky' or something... or maybe we should just keep quiet about it, buy up some old lifeless D-12's and make some money!  ;)

Keith
Title: Re: AKG D12 repair attempt...
Post by: s2udio on June 27, 2009, 04:39:58 PM
Just comleted a complete stripdown to capsule level (this one also suffering from moisture damage),and didnt respond to well to just loosening screws
and sweeping on the signal gen ....30-5k.
So had to............ Bite the Bullet and strip her down .......   ohhhhh...................Tried it out a few hours ago
Yeh hah !!....thanks of course to all here.... :)
Lots of capsule stripdown photos available .........If ok will put them up with a basic rundown of the process  ;D
Title: Re: AKG D12 repair attempt...
Post by: KarlH on June 28, 2009, 04:53:56 AM
yes please, more photos of the process.
I'm girding my loins and looking for the time to fix one here.

big thanks to keef for going where no man has gone before.

karl
Title: Re: AKG D12 repair attempt...
Post by: s2udio on June 28, 2009, 05:13:13 AM
OKwill get working on posting them in the next couple of days
(Bit busy at the mo) !
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on June 29, 2009, 07:08:03 AM
big thanks to keef for going where no man has gone before.

Nice for sure, but let's also not forget Roddy, IIRC he originally posted 'the mighty trick' with the signal-generator here.

Cheers,

  Peter
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on June 29, 2009, 09:48:04 AM
Oh, I must redirect any gratitude entirely towards Roddy. He-da-man.

Keith
Title: Re: AKG D12 repair attempt...
Post by: s2udio on June 29, 2009, 12:33:43 PM
Hot of the press !
AKG D12E strip

Click on the pics for large zoom images.........

I have not included pics of the housing stripdown ,just the capsule (Bass chamber removed)
You will need good eyes, or a magnifier,  and most important....Patience
Here we go..............
Mark a line down the side of the capsule,...i used the two mounting holes on one side as a guide, and put a line on the top cover ,to aid orientation on reassembly.

Carefully loosen the six screws at 60deg intervals.
Remove the two screws with wire clamps attached.
NOTE......Be careful with the screwdriver at all stages as the magnet will pull it into the centre of the capsule !!
Gently Bend the sleeved lead-in wire up.....(the thin diaphram wire enters the sleeve at the bottom)
You can now remove the sleeves .....mine was free to lift off,revealing the solder joint
Remove the remaining four screws and ...........gently break any seal (if not loosened already) .......
by very gentle leavering of the cover on one side and then the other
Slowly remove the capsule cover.......mine seperated between the first and second gaskets,which left the fine wires pinned down..
another one may not.....at all stages........Be Carefull !.....Slowly does it !

(http://img198.imageshack.us/img198/3643/50692561.th.jpg) (http://img198.imageshack.us/my.php?image=50692561.jpg)

(http://img34.imageshack.us/img34/6167/30182693.th.jpg) (http://img34.imageshack.us/my.php?image=30182693.jpg)

You can now see the diaphram and gaskets.............one which I left attached to the cover.
There are four gaskets......two above and two below the diaphram .
The Moisture damage (Oxide) is now evident,and by gently pushing on the diaphram ..it stuck ..due to the oxide dust and dirt in the gap !
I marked the gaskets and capsule with a line to align with the body mark made earlier.
Gently remove the second gasket to free the thin diaphram wires.

(http://img196.imageshack.us/img196/8363/91281589.th.jpg) (http://img196.imageshack.us/my.php?image=91281589.jpg)

Get the iron hot and re tin the joints with a small solder application, I used an extra drop of SML flux at this point to keep it clean .
While keeping the solder at melting point GENTLY tease the fine wire to the top of the lead in wire ...
I used a small plastic tiewrap end along with the iron to stroke the fine wire to the tip and finally to freedom !
Repeat for the other side

(http://img196.imageshack.us/img196/5083/85060421.th.jpg) (http://img196.imageshack.us/my.php?image=85060421.jpg)

(http://img41.imageshack.us/img41/9725/39590728.th.jpg) (http://img41.imageshack.us/my.php?image=39590728.jpg)

I found the best way to lift off The Diaphram ,was to delicately pinch each wire end between thumb and forefinger (two hands) and slowly lift / tease it to a safe haven !
A Deep Breath (easily blown away)
The Diaphram can now be lifted to safety .......................!!

(http://img198.imageshack.us/img198/7393/85892685.th.jpg) (http://img198.imageshack.us/my.php?image=85892685.jpg)

Internals in order of dissasembly (R to L)
 
(http://img41.imageshack.us/img41/3388/72054103.th.jpg) (http://img41.imageshack.us/my.php?image=72054103.jpg)

The two lower gaskets (which i numbered for reference). The bottom one was stuck firmly to the body...
Which had to be removed to facilitate cleaning of the oxide deposits from the surface.

(http://img189.imageshack.us/img189/8094/13863856.th.jpg) (http://img189.imageshack.us/my.php?image=13863856.jpg)

Pull back the lead in wires from the entry holes (secured out of harms way by a tiewrap round the body).
You can see the corrosion, the oxide comes off in a white dust............

(http://img189.imageshack.us/img189/1986/110nob.th.jpg) (http://img189.imageshack.us/my.php?image=110nob.jpg)

Ready for a clean !

Cleaned the oxide and rust away with a piece of scotchbrite followed by fine emery,

The all important diaphram gap was scraped with a scraper cut and shaped  from a lighting gell sheet .

Scape round and round till your wrist hurts !

Finished the gap and top with a stiff bristle (bristles cut short) paint brush.
Then a good blow out with a compessed air blower..................no damage was sustained during this process and it also cleans the small  holes that lead to the acoustic chamber

Most important......keep away from iron particles....and then
Place the body in a clean plastic bag to keep it CLEAN !!........... until ready for reassembly.

(http://img32.imageshack.us/img32/7017/55349887.th.jpg) (http://img32.imageshack.us/my.php?image=55349887.jpg)

(http://img29.imageshack.us/img29/3451/60853107.th.jpg) (http://img29.imageshack.us/my.php?image=60853107.jpg)

At this point I also cleaned all the other mic parts,suspension,etc......the grills were also blasted with comp air as a lot of the fibers on the inside were loose and free....
Brutal but the result was a very good proportion remained intact ....

Reassembly Time .........

Fit the fourth (or last removed) and third gaskets,using the guide marks made earlier
Using the Diaphram lift,method...... refit the diaphram........using the align mark...

(http://img29.imageshack.us/img29/2718/38468549.th.jpg) (http://img29.imageshack.us/my.php?image=38468549.jpg)

(http://img29.imageshack.us/img29/9264/51841960.th.jpg) (http://img29.imageshack.us/my.php?image=51841960.jpg)

(http://img34.imageshack.us/img34/1949/85029923.th.jpg) (http://img34.imageshack.us/my.php?image=85029923.jpg)

To align the bottom gaskets/diaphram I delicately teased the wires into the positions as to exit the gasket near the
lead in wire holes..........when happy that diaphram looks central....... and wires are in position,
drop on the second and first gaskets
A very light touch (use small piece of thin flat plastic)  to the dome should reveal silky smooth movement.

Fit the Capsule top and fit four of the screws,(not the clamp bracket ones) tighten to pull down the top....(check the position of those wires !)
then release the tension so as to leave the top slightly loose.

(http://img189.imageshack.us/img189/2748/51453724.th.jpg) (http://img189.imageshack.us/my.php?image=51453724.jpg)


Reinstate the lead- in wires and (the tricky bit) tease the diaphram wires onto the lead-ins, leaving a small bit of slack.

NOTE the diaphram wires must run up parallel with the lead-in wire,so as not to break them when replacing the sleeve and clamping .

(http://img189.imageshack.us/img189/428/79853655.th.jpg) (http://img189.imageshack.us/my.php?image=79853655.jpg)

(http://img35.imageshack.us/img35/5403/20102590.th.jpg) (http://img35.imageshack.us/my.php?image=20102590.jpg)

Resolder and check for continuity ....210 ohms in my case.

Next Test and align as per Roddys procedure ( carefull with the exposed wire ends)
When its singing happily,and the screws are tensioned to feel.........tight ......but not to tight !!

Slip  the sleeves over the wire ends,......gently bend them over  (watch the diaphram wires.!!) and........
Replace the clamps and screws, tightening as per the first four

(http://img35.imageshack.us/img35/1096/98622815.th.jpg) (http://img35.imageshack.us/my.php?image=98622815.jpg)

(http://img198.imageshack.us/img198/841/210idr.th.jpg) (http://img198.imageshack.us/my.php?image=210idr.jpg)

Retest with a sweep on the sig gen ...(small errors can be corrected at this stage,if all tested good the first time
 
Reassemble the mic complete and Hey Presto a full working D12 with...."Deep, stentorian bass!" quote Keef

(http://img198.imageshack.us/img198/3610/211hvx.th.jpg) (http://img198.imageshack.us/my.php?image=211hvx.jpg)

(http://img41.imageshack.us/img41/4555/212mai.th.jpg) (http://img41.imageshack.us/my.php?image=212mai.jpg)

Many thanks to Roddy for his posting of the sig sweep method ... and Keith for bringing the subject up for scrutiny

ps i will probably be editing this ...... as and when i notice anything that i might have missed ,

Hope this is of help to a few ageing D12's
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on June 29, 2009, 02:59:44 PM
I am humbled by the work of others.

This write-up is a work of magnificent stature! Thanks s2udio!

-Keith
Title: Re: AKG D12 repair attempt...
Post by: s2udio on June 29, 2009, 03:27:17 PM
Thanks Keith
Glad to have a chance to contribute to this Nirvana of audio hardware information !  ;)

Regards
Paul
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on June 29, 2009, 04:27:56 PM
Thanks all, nice  :)
Title: Re: AKG D12 repair attempt...
Post by: KarlH on July 09, 2009, 12:08:30 PM
A HUGE THANK YOU and many cases of virtual beer to Roddy, Keith and especially to Paul for the step by step tutorial!!

Due to the amount of rust and crud, I had to tear it down a la Paul (...the next time, I will not ignore the magnifying glass suggestion....) but, after a few hours and a few tense moments, I've got a proper D12!

Now to see about the 10 euro D19 from the boot sale.....

Thanks guys,

Karl
Title: Re: AKG D12 repair attempt...
Post by: s2udio on July 17, 2009, 06:45:51 PM
Good to hear Karl....congrats on the repair   ;)
I just love these mics.....after my first drum session 35 yrs ago... ohh that bass drum !!

Title: Re: AKG D12 repair attempt...
Post by: clintrubber on October 22, 2009, 10:40:34 AM

Think I've found the reason why so many of these mics have the broken surround.

I mean, D12E came with a SA31-clip, which didn't gave a snug fit. So I eBayed
a SA30, as also indicated in an older D12E-doc, but &*%^$, thAts a tight fit !  :o

Can well imagine not all broken surrounds are because of dropping, but also being caused
by squeezing the mic in that tiny '30... 

My -E is still fine though, but it's certainly something I hope to keep in mind.

FWIW...


Bye,

  Peter


PS
Why nobody makes new surrounds for the D12(E) is beyond me,
a decent living could me made out of this I expect.
Title: Re: AKG D12 repair attempt...
Post by: OneRoomStudios on October 24, 2009, 01:22:34 AM
Two (dumb) questions:

1. Where are you guys hooking the signal generator to the capsule? Before or after the windings?

2. Are all of you using <200Ω output impedance generators? My generator has a 600Ω output impedance so I may have to borrow one from somewhere...
Title: Re: AKG D12 repair attempt...
Post by: s2udio on October 24, 2009, 05:53:34 AM
Just hook it up to the output leads of the mic........ green/blue
The output impedance dont really matter...as long as you can get it to
oscilate......I used the headphone output of my laptop with software sig gen
Just start with the output gain very low at 1khz ,and increase untill it gently sings
Then sweep from 50 to -5k listening for any nastys...
Title: Re: AKG D12 repair attempt...
Post by: craigmorris74 on November 01, 2009, 04:03:50 PM
Is there any chance of recovering lost bass if the diapragm has a small hole and dents?
Thanks,
Craig
Title: Re: AKG D12 repair attempt...
Post by: Jeremy.Starseed on November 01, 2009, 05:21:22 PM
Hi. I have a D12 which has two knobs on the back. Do any of you know what these do?

Mic seems to be in fair condition...but I will probably have to give it the Prodigy treatment after reading this great thread.

So, the knobs...filter, impedance...pattern select...what could it be they're meant to do?

Title: Where is that AKG D12 Disassembly/cleaning tutorial??
Post by: ihscoutlvr74 on November 02, 2009, 06:52:52 PM
I saw a very detailed step by step method to take apart and clean a D12 with pics here somewhere and can't find it.  Can someone reply with the link?  Thanks, Nathan
Title: Re: Where is that AKG D12 Disassembly/cleaning tutorial??
Post by: clintrubber on November 02, 2009, 07:00:12 PM
I saw a very detailed step by step method to take apart and clean a D12 with pics here somewhere and can't find it.  Can someone reply with the link?  Thanks, Nathan

Where did you search  ??? ::)
Title: Re: AKG D12 repair attempt...
Post by: MagnetoSound on November 03, 2009, 04:06:21 AM

You mean the one from s2udio just a few posts up from here?
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on November 03, 2009, 06:45:42 AM

You mean the one from s2udio just a few posts up from here?


I merged the new topic asking for this thread with this thread, saved our friend a search for 'AKG + D12 + repair'.

All fine...
Title: Re: AKG D12 repair attempt...
Post by: ihscoutlvr74 on November 03, 2009, 06:47:44 PM
Yay! Success!  After I get all the flocking off the inside and the rust off the grills - is there a paint or clearcoat I could apply that will not clog the mesh to keep it from rusting again?   
Title: Re: AKG D12 repair attempt... Further advice needed
Post by: Vik on March 21, 2010, 12:10:17 PM
Hi all!

Hot of the press !
AKG D12E strip
...
Hope this is of help to a few ageing D12's
Congratulations and a huge "thankyou" for creating THE best online resource on D12 repairs on the net! It certainly improved my D12, and without this thread, I would not have known where to even start with it.

I still have a question though. I'm not sure if I should be happy with the sound I'm getting now. I have reseated the diaphragm already, but when I A/B the D12 with a D112 on a bass cabinet at low volume, the D112 has *lots* more bass, making the D12 sound kind of midrangey in comparison. I've put up a sample here:

http://www.avatarzenekar.hu/files/d12_left_d112_right.mp3 (http://www.avatarzenekar.hu/files/d12_left_d112_right.mp3) 

Is this how it's supposed to sound, or is there still something wrong with it?


About the mic:

It's an Echolette D12 and it appears to have been used as a vocal mic and has definitely has been dropped or whacked against something at some point in its life. The bass reflex chamber got loose and had been soldered back on. One edge of the grille is dented. The front of the grille was in a disgusting state (I soaked it in warm soapy water and eventually got the gunk out, as well as most of the fine cloth that came out with it). There is something is loose inside the capsule that rattles when I turn the mic around and the rattle gets picked up by the mic. It sounds as if a tiny piece of solder was rattling around inside. It's definitely not in the bass reflex chamber as the sound persisted when I removed the chamber and the diaphragm. I can live with it if I have to, but it would be nice to know what it is.

The bass reflex chamber does appear to have small piece of paper inside it, visible through the hole when the transformer is removed (is this normal?). It is not blocked though, I could blow through it.

I removed the diaphragm, carefully lifting it off against the tiny wires and I ran a magnetised screwdriver and some compressed air over the magnet surface to make sure there were no rust particles left in there. I reseated the diaphragm and did the sine sweep between 50 - 5000Hz. The diaphragm gives an even tone that fades in volume to just barely audible at 100Hz and below. There may be very minimal buzz at around 200Hz or thereabouts, but that could even be 'normal' for the small diaphragm.

Is it normal to have paper in the bass chamber? Any idea what could be loose inside the capsule and how to open that part up?

Thanks in advance.

Cheers,
Vik

Title: Re: AKG D12 repair attempt... Further advice needed
Post by: s2udio on March 21, 2010, 03:27:55 PM

I removed the diaphragm, carefully lifting it off against the tiny wires and I ran a magnetised screwdriver and some compressed air over the magnet surface to make sure there were no rust particles left in there. I reseated the diaphragm and did the sine sweep between 50 - 5000Hz. The diaphragm gives an even tone that fades in volume to just barely audible at 100Hz and below. There may be very minimal buzz at around 200Hz or thereabouts, but that could even be 'normal' for the small diaphragm.

That diaphragm needs to be fully removed........hope you did using the comp air !...... and the Gap needs to be fully scraped clean to the bottom.......as in the procedure
simply running a magnetic screwdriver and a puff of air will not do the job !...as the gap will be full of oxide .....non magnetic...
The sweep should be audible down to about 40 hz........with no buzz at any frequency...sounds like you may have to try again !
As for the paper in the hole.......dont recall any in mine..........from what i can gather from your post it is still not right
Title: Re: AKG D12 repair attempt... Further advice needed
Post by: Vik on March 21, 2010, 05:07:32 PM
Hi, thanks for the quick response!

That diaphragm needs to be fully removed........hope you did using the comp air !...... and the Gap needs to be fully scraped clean to the bottom.......as in the procedure
simply running a magnetic screwdriver and a puff of air will not do the job !...as the gap will be full of oxide .....non magnetic...
I wish I had taken some pics. The capsule isn't so badly oxidised on mine as it was on yours, but I'll clean it anyway (although I was really hoping I won't need to...) On my mic, the diaphragm and the spacers are all stuck to the grille, meaning that I could easily pull the whole thing away as far as the tiny wires would allow (and that was when I applied the air, with the diaphragm at a 'safe' distance).

How did you get the paper shims to separate? Mine are firmly stuck together, and this makes it impossible to clean the grille, or to get a good view of the diaphragm.

The sweep should be audible down to about 40 hz........with no buzz at any frequency...sounds like you may have to try again !
It is audible, but quiet -- it's quiet enough that I have to put my ear next to it when the laptop is next to the mic with its fan turning on 'low' (the laptop is needed as it's generating the test signal, unfortunately).

As for the paper in the hole.......dont recall any in mine..........from what i can gather from your post it is still not right

Did you listen to the sample or are you just taking my word on it? :)

Anyway, I'll pull it to bits again, either tonight or next weekend. I've got some really thin wire so I'll try to practice soldering it first :) I'll be taking some pics this time.

Cheers,
Vik

UPDATE: I did pull it to bits and put it back together. It's too late for testing it with the bass amp, but it does not appear to sound better to me. Will test tomorrow.
Title: Re: AKG D12 repair attempt...
Post by: s2udio on March 22, 2010, 01:55:15 PM
The procedure needs to be followed as per the instructions............there are no shortcuts....the diaphragm must be unsoldered and removed !
seperate the gaskets with a scalpel......patiently......
If the diaphram wires are not routed and clamped correctly.......no go....this is why capsule needs to be completely stripped and cleaned..
without cleaning the gap properly and carefull alignment you will be wasting your time.
If you cannot hear the capsule sing,........... carefully increase the laptop sig gen output...but not to overdrive and burn the coil......
unfortunatley there is no way i could tell you at what point that would happen.......you are turning it into a speaker so
dont over do it.........maybe i should have taken a voltage measurement............all 3 i have repaired were quite audible over
any laptop noise...........proceed with patience
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 22, 2010, 04:08:48 PM
Hi there,

A bit late, but here's the writeup of what I did:

First I pulled out the transformer and attempted to remove the piece of paper in the bass chamber. I was unable to pull it out with tweezers, but I got a better look of it. It appears to be some kind of spongy material with self-adhesive backing. It must have been glued to the back of the chamber originally for taming the resonance. It's probably not too good to have it detached though. Problem is, I think I'll need a hammer to open the chamber up, and I really hope I won't break it. Maybe I should get a spare chamber instead, mine was damaged already anyway...

This is the best picture I managed to take through the little hole at the bottom of the bass chamber:
(http://www.avatarzenekar.hu/files/d12/d12_bass_chamber_small.png)

For reference as I have not seen pics elsewhere, this is how the transformer looks like:

(http://www.avatarzenekar.hu/files/d12/p1000687_small.jpg)
(http://www.avatarzenekar.hu/files/d12/p1000689_small.jpg)

And this is how the front of the capsule looks on mine:
(http://www.avatarzenekar.hu/files/d12/p1000688_small.jpg)

Next I took apart the shockmount and removed the capsule. Note: somehow I got lucky the first time and failed to notice how annoying it can be to put the shockmount back together. Especially that there is a hungry magnet ready to swallow the screws through the went holes on the capsule's side, into tweezerland. But I'm getting ahead of myself :)

The unsoldering and re-soldering of the tiny wire was actually easier than I tought it would be. I did practice with a similar gauge wire beforehand though. The plastic tie-wrap is definitely handy for moving the wire in and out of the solder.

I took off the capsule with grille, brass ring, paper shims & all. The coil gap appeared to be clean but I used 1000 grade sandpaper really gently to make sure it really is, and blew it out with compressed air afterwards. I made sure I can see the brass shining at the bottom of the gap and that there is no oxide stuck in there.

Here's some pics of the mic as disassembled:
(http://www.avatarzenekar.hu/files/d12/p1000690_small.jpg)
(http://www.avatarzenekar.hu/files/d12/p1000691_small.jpg)
(http://www.avatarzenekar.hu/files/d12/p1000692_small.jpg)

I used a thin screwdriver for separating the shims from the brass. This is the part most likely to increase your grey hair count. Be *really* careful with that screwdriver / scalpel / whatever!

Once I got the brass and the membrane to separate, I noticed that the grille comes out as well -- it's held in by the edges of the same six screws that hold the diaphragm assembly in place. In fact, the grille was probably the source of the misterious rattle I heard earlier. I have already loosened the screws a bit, and it probably caused the grille to come loose. Either that or it had something under it that was rattling against the diaphragm. I'll never know, but the noise is gone. This is what the other side of the membrane looks like. There appear to be some fine oxide particles embedded, but nothing serious. Whatever's stuck in the membrane ist there to stay though, I will not risk trying to remove it:

(http://www.avatarzenekar.hu/files/d12/p1000693_small.jpg)

So I tried to make sure that the gap is clear, the coil is clear, and the membrane is as clean as possible. I then reassembled everything. I did not have the holders for the solder joint. Whoever last repaired the mic just added some chewing gum to hold it in place. I replaced this with some blu-tac which may not last as as long but is much less disgusting :)

I tried the sine wave test with no rattle but no improvement either. I then tested the mic on the bass cab this morning and again I did not notice any improvement. I will try to realign the capsule but I'm not too confident that it would help. In any case I'll use the opportunity to mike it up and record the sine sweep, to make sure I'm not missing anything. Any suggestions on what to try next?

Cheers,
Vik

UPDATE: I forgot to add that larger versions of each pic are available at the same place here: http://www.avatarzenekar.hu/files/d12/ (http://www.avatarzenekar.hu/files/d12/)
Title: Re: AKG D12 repair attempt...
Post by: s2udio on March 22, 2010, 05:03:06 PM
Check this thread......thats not the D12 i know  :-\
and may not be what you think it is...........never seen one like this myself....??
http://recforums.prosoundweb.com/index.php/t/13463/0/
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 22, 2010, 08:45:58 PM
Check this thread......thats not the D12 i know  :-\
and may not be what you think it is...........never seen one like this myself....??
http://recforums.prosoundweb.com/index.php/t/13463/0/

Well, what I see and hear seems to relate to what folks say about the older D12 mics. Mine is definitely one of the older types around. It's (re)branded as an Echolette, the metal plate around the base says "D12/200", serial number 1302. The writing faded a lot but the serial number is punched into the metal.

Have the ones you've opened include a transformer? If yes, was it stuffed into the front part of the bass chamber? Maybe I'd get more low end by bypassing the tranny... I just looked at the pics of the assembled mic from your writeup. It looks as if the newer mics (including yours) had their bass chamber made out of plastic instead of metal and did away with the transformer as well. If this really was the case, that would explain a lot about the sonic differences. On my mic, the resonant area of the bass chamber is tiny as the entire front is used for the transformer. And even the space at the back is damped (even more now that the damping material got loose).

If you happened to have a pic that shows the bottom half of the mic in more detail, I would much appreciate it.

Thanks again!

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: andre tchmil on March 23, 2010, 07:03:07 AM
A few weeks ago I posted here my problem with a D12.
Both tails of the membrane wire are broken off.
Now I'm looking for a replacement membrane.
Title: Re: AKG D12 repair attempt...
Post by: s2udio on March 23, 2010, 07:14:50 AM
That bass chamber is not a bass chamber......its the transformer can.....the early ones were not fitted with a chamber !
and did not have a pronounced bass response as the later ones ....
the D12 service document
http://www.akg.com/mediendatenbank2/psfile/datei/85/d12443e17c7c62d7.pdf
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 23, 2010, 10:06:25 AM
That bass chamber is not a bass chamber......its the transformer can.....the early ones were not fitted with a chamber !
and did not have a pronounced bass response as the later ones ....
the D12 service document
http://www.akg.com/mediendatenbank2/psfile/datei/85/d12443e17c7c62d7.pdf

Excellent document, thank you! I don't see the transformer inserted anywhere on the diagrams though. In any case, on mine the transformer can appears to have been hacked into the chamber after the fact. I've noticed the sloppy assembly (the outer can has been cut open slightly and the inner can hammered into it with a piece of rubber or soft plastic between the two. The hole through which the spongy damping material is visible is in the bottom of the inner can.

Should I try to get the inner can out, close up the chamber and rewire the bypassing the transformer?

UPDATE: I've put up some more pics to the same place ( http://www.avatarzenekar.hu/files/d12/ (http://www.avatarzenekar.hu/files/d12/) ) showing all aspects of the mic (transformer holder, serial number, etc) if anyone is interested.

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: s2udio on March 23, 2010, 01:07:12 PM
If it was a bass chamber it would connect to the capsule at the back as in the service document to allow airflow into it!
as i said......i think its just the transformer shielding can....from what i can see.....any pics of the back of the capsule ?
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 24, 2010, 08:24:03 AM
If it was a bass chamber it would connect to the capsule at the back as in the service document to allow airflow into it!
as i said......i think its just the transformer shielding can....from what i can see.....any pics of the back of the capsule ?

Well, it was a bass chamber and it's connected as it should be. But it probably stopped functioning as such when some git hammered another can into it and reduced its volume to about the quarter of what it was before.

I've put up a ton of pics, here's one of the back:
(http://www.avatarzenekar.hu/files/d12/p1000706_small.jpg)
The tube coming out of the back of the capsule is somewhat broken, so it has been soldered to make it stay in place. But I have checked the airflow and even blew through it with compressed air.

Couple more pics from other aspects:
(http://www.avatarzenekar.hu/files/d12/p1000707_small.jpg)
(http://www.avatarzenekar.hu/files/d12/p1000709_small.jpg)
(http://www.avatarzenekar.hu/files/d12/p1000705_small.jpg)

On the original large versions, you can sort of see how the transformer can was hacked in, although these pics are not very good. This was the best I could do in a hurry, and without taking it apart again. (larger pics here: http://www.avatarzenekar.hu/files/d12/ (http://www.avatarzenekar.hu/files/d12/))

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: s2udio on March 24, 2010, 01:00:34 PM
Ahh now i can see ......low Z D12 with a transformer fitted in can......?
remove trannie ....seal chamber......and make sure airflows from the small hole in the centre of the can in to it
That transformer is the hack ......remove the screws on the back of the capsule , remove the chamber and restore it ..
looks like that solder job may be blocking the airflow ?
Title: Re: AKG D12 repair attempt...
Post by: SSLtech on March 24, 2010, 05:27:05 PM
Oh yeah... I have one here of that vintage also...

One of the wires is shortened... and the paper spacers are largely disintegrated.

I'm plucking up courage to go back into finishing the job off...

...still note enough courage, yet!!!

Keith
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 24, 2010, 07:50:24 PM
Ahh now i can see ......low Z D12 with a transformer fitted in can......?
remove trannie ....seal chamber......and make sure airflows from the small hole in the centre of the can in to it
That transformer is the hack ......remove the screws on the back of the capsule , remove the chamber and restore it ..
looks like that solder job may be blocking the airflow ?

I'll try to just pull out the tranny and seal the chamber up to see if it helps first. And I'll try to get the chamber sorted out. The solder job does not block the airflow (I've checked). the chamber didn't break off completely just partially, so the solder is holding it from the outside. The impedance (resistance actually) of the transformer is actually *very* high, I measured just over 2kOhm with a multimeter. The mic says D12/200 -- 200 ohms. Does anyone know if that's meant to be with or without a transformer? I think they made a 60Ohm version as well.
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 24, 2010, 07:58:00 PM
I'm plucking up courage to go back into finishing the job off...

Hi Keith,

Personally I expected the soldering of the fine wire to be harder. I never tried to solder anything like that before, so I got a similar gauge wire from an electronics supplier and practiced on that first. I had the iron on 300degC, touched it to the thick wire and pulled the thin wire away with a plastic tie-wrap like Paul suggested. Having one end shorter means you got more of a challenge, but I've found that actually fiddled a lot more with putting the shockmount back together. So I'd say go for it! :)

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: s2udio on March 25, 2010, 05:23:53 AM
I measured just over 2kOhm with a multimeter. The mic says D12/200 -- 200 ohms. Does anyone know if that's meant to be with or without a transformer? I think they made a 60Ohm version as well.
Yup spot on 200ohm........older ones 60............dump the trannie i am sure thats not meant to be there !
Nice pics btw.........sure to help the more ancient D12's to rebirth !
Title: Re: AKG D12 repair attempt...
Post by: EmRR on March 25, 2010, 11:20:00 AM
If you're getting 2K resistance on that transformer, its either 1) failing in the direction of open, or 2) a hi-Z (50K for feeding an instrument input) step-up someone hacked in.  Try it into a direct box and see if it sounds better, before you do anything.  That would confirm or deny hi-Z step-up intention. 
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 25, 2010, 08:56:04 PM
OK, I have removed the transformer and reconnected the wires directly. Output resistance is now 50Ohm. I have attempted to restore the bass chamber to it original purpose. To this end I heated the bass chamber with the soldering iron until I was able to remove the insert. It turned out to be an old school transformer housing -- the little hole was originally there for the cable to enter the case. In fact, whoever soldered it in just cut the cable off because it was easier than unsoldering it.

In the bass chamber behind the transformer housing there was a piece of spongy foam and what I thought to be paper turned out to be a small piece of insulating tape. I cut and filed a disc of the right size from a thin steel sheet, to replace the front of the bass chamber. I temporarily soldered it in place and gave it a go.

Unfortunately there is still no bass... The only difference was that the output signal got about maybe 10dB quieter. On the other hand, if I hook it up to my sound card output and feed it a sine wave, that's noticeably louder -- naturally the sound card is better at driving 50Ohms than 2000. This way it is now noticeable that from about 125Hz down there is some buzzing happening at higher volumes (above that it's fine). It appears the loudest around 90Hz. Moving the diaphragm doesn't really help. I wonder if I should add another paper shim (if I loosen the screws, it gets a little bit better). Or perhaps I should check the gap again... Any ideas?

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 25, 2010, 09:08:11 PM
If you're getting 2K resistance on that transformer, its either 1) failing in the direction of open, or 2) a hi-Z (50K for feeding an instrument input) step-up someone hacked in.  Try it into a direct box and see if it sounds better, before you do anything.  That would confirm or deny hi-Z step-up intention.  

I forgot to add that I did try the DI-box, but it didn't make any obvious sonic difference. After desoldering the transformer, I measured it again and got the same resistance 2kOhm. It was wired with a common ground, I made the measurement the same way.

UPDATE: Could it be that the transformer was there to boost the output level (voltage)? I think apart from this it also contributed some odd-order harmonics which helped to bring out the retro mid-range growl of the mic (which actually sounds cool on a bass amp but doesn't help with the low end).
Title: Re: AKG D12 repair attempt...
Post by: andre tchmil on March 26, 2010, 06:35:07 PM
Don't dump the membrane !!  :P
Title: Re: AKG D12 repair attempt...
Post by: MagnetoSound on March 27, 2010, 02:52:15 AM

No harm in trying another shim. It is possible that what is already there is less than even all the way round. Do you have a good clean surface on the bottom of the diaphragm edge?

Title: Re: AKG D12 repair attempt...
Post by: Vik on March 28, 2010, 06:48:59 PM
OK, I think I'll give up on this particular D12 as a kick mic, and I'll reassign it to a bass amp mic role. After the last round of work, there is some improvement, but not really more bass. Overall, it just sounds a bit cleaner to me. I actually like how it sounds combined with the D112. The D112 adds the deep end and the highs while the D12 brings out the Warwick growl that I love. I moderately regret that I dumped that transformer, it was adding some transformer distortion that was good for the same purpose.

Over the weekend I have desoldered the membrane again, added an extra shim (nothing fancy, just a single sheet of 150g photo paper). While I was at it, I've used a magnetised phillips screwdriver to pick away all the "dirt" from the membrane which are of course little metal oxide particles. This takes a lot longer to do it properly than I would have thought. I've done this already but not thoroughly enough -- just running a screwdriver over the surface won't do it. I also made sure that there was good airflow through the core of the capsule (between the hole under the membrane and the entrance to the reflex chamber). Testing with a sine wave, now there is no buzz from the membrane (which now makes it a lot harder to hear below 150Hz). I am able to tighten all six screws quite tightly without buzz appearing.

Question: any idea what the other three screws (the recessed ones) are for? Looking at the service document from above (http://www.akg.com/mediendatenbank2/psfile/datei/85/d12443e17c7c62d7.pdf (http://www.akg.com/mediendatenbank2/psfile/datei/85/d12443e17c7c62d7.pdf), page 3), it appears as if they might be for adjusting the spacing of something inside the capsule. Could they be used for tuning something like the position of the magnet relative to the gap or something?

The other thing I can think of is that the bass chamber has some gaps where I closed it up, due to me not doing an 'airtight' solder. That's probably not really fortunate for a Heimholtz resonator, but I would be surprised if it made that much difference. Any more ideas or should I just try to ebay another one instead? :)

Anyway, thanks for the help so far. Even if I didn't manage to get the bass response I expected, I still learned a lot from this thread.

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 29, 2010, 09:14:25 AM
One more thing: This was mentioned a couple of times already, but I think it wasn't emphasised enough: Do not ever,  ever, ever, ever put a screwdriver near the magnet (like for picking off metal particles next to the coil) while the membrane is on. If you want to remove the magnetised bits of oxide from the membrane, you MUST unsolder and remove it (it's not as hard as it sounds).

I knew about the magnet and I thought I was holding the screwdriver tight. But the magnet just grabbed it in a blink of an eye, and before I realised, the screwdriver was already very firmly stuck to the magnet, pinning the membrane down. I was very, very, very, very lucky that the screwdriver was a flat head and it landed with the flat side. Otherwise I would now have a hole in a membrane and I would be crying like a little girl...

I thought I'd share this for those who are, unlike me, willing to learn from other people's mistakes :)
Title: Re: AKG D12 repair attempt...
Post by: rodabod on March 29, 2010, 11:43:39 AM
the magnet just grabbed it in a blink of an eye, and before I realised, the screwdriver was already very firmly stuck to the magnet, pinning the membrane down.

You want to try repairing ribbon mics.
Title: Re: AKG D12 repair attempt...
Post by: Vik on March 29, 2010, 12:32:29 PM
the magnet just grabbed it in a blink of an eye, and before I realised, the screwdriver was already very firmly stuck to the magnet, pinning the membrane down.

You want to try repairing ribbon mics.

Got any I can practice on? :)
Title: Re: AKG D12 repair attempt...
Post by: craptical on March 29, 2010, 04:47:25 PM
I moderately regret that I dumped that transformer, it was adding some transformer distortion that was good for the same purpose.


Just put the tranny in a box w. xlrs in-out and you can use it whenever you like! :)

/Dave
Title: Re: AKG D12 repair attempt...
Post by: bkbirge on April 06, 2010, 06:37:24 PM
A bit of necrothreading here but I can't find the answer with a search...
I've got a D12(e?) with an on/off switch installed. It sounds great, nice and punchy with rich low mids EXCEPT it has a horrible buzzing sound that is too audible to really make the mic usable. I haven't put a scope on it but I'd guess it's a ground hum harmonic. Anyone have any ideas what could be causing it? It did this at the old studio and I thought it was my wiring but it also does it at the new place. How would you experts go about troubleshooting this? Thanks! - Brian
Title: Re: AKG D12 repair attempt...
Post by: Vik on April 07, 2010, 04:25:28 AM
Hi there,

Why, the thread's still fresh :) I just got too busy to waste more time on my D12, and decided to postpone my reply until I actually got something new to say. (Thanks Dave for the suggestion to box up the transformer, I will very likely do that).

When I pulled my D12 apart, there was terrible ground hum when the capsule was no longer earthed. It is normally earthed through the chassis / internal shockmount, and when I pulled it out for disassembly, it started to buzz straight away. So checking the earth connection would be a good place to start, I think.

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: bkbirge on April 07, 2010, 02:43:47 PM
Thanks Vik, I'll look there tonight! - Chip


Hi there,

Why, the thread's still fresh :) I just got too busy to waste more time on my D12, and decided to postpone my reply until I actually got something new to say. (Thanks Dave for the suggestion to box up the transformer, I will very likely do that).

When I pulled my D12 apart, there was terrible ground hum when the capsule was no longer earthed. It is normally earthed through the chassis / internal shockmount, and when I pulled it out for disassembly, it started to buzz straight away. So checking the earth connection would be a good place to start, I think.

Cheers,
Vik
Title: Re: AKG D12 repair attempt...
Post by: zebra50 on June 11, 2010, 06:00:13 AM
I just wanted to say a big thanks for this thread.

I've just serviced one of these that was covered in black dust, and the photos were a great help in getting it going again.

THANKS!
Title: Re: AKG D12 repair attempt...
Post by: OneRoomStudios on July 15, 2010, 01:16:52 AM
I want to add my name to the list of thank you's. I just got one of my D12E's working like new again! The pictures were a huge help. Desoldering and resoldering those tiny magnet wires sure is a PITA though. Tuning the capsule wasn't as hard as I thought it would be once everything was cleaned up.

It really is great to have the resource of this community. I sincerely thank everyone involved!
Title: Re: AKG D12 repair attempt...Seeking parts
Post by: michaelfav on August 17, 2010, 06:58:54 PM
I too recently dug into my faulty D12 after I tried to sell it on eBay and got it returned broken.  The membrane filament wire on the diaphram shattered.  Does anyone know where I could locate one?  I have contacted AKG in Austria and informed they discontinued repair two years ago.
Title: Re: AKG D12 repair attempt...
Post by: StudioSQ on August 18, 2010, 12:49:44 PM
just the sine wave/screw thing worked for me too. long live prodigy pro!
Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on August 21, 2010, 01:14:49 PM
hey guys!
some fantastic info in here! thanks very much to all of you.

i have a quick question regarding a d12e that i bought. i was led to believe that it was 'faulty' (lacking in bass), but now that i have it and have compared it to other mics, i'm not sure that it is.


it sounds fine, very 'wooly' and a little dull on speech.

the only hint of a problem i can find is that it reproduces 60hz + below at a much lower level than say, a d112.


i recorded a sine wave curve and it shows the d12 getting louder as the freq increase, but with d112, it's pretty much consistent.


big question is, is it faulty, or is that the way d12s are?

the mic is exceptionally clean. in fact, it may as well be new! inside and out!


**update.
sadly i don't have a kick drum or decent bass instrument to test with, but i sent a recording of a kick drum to a sub and miced with
d12,d112 and sm7b in that order.
clip is at www.webforni.com/steen/3mics.mp3

seems like the mic might be fine to me? but i'm still made nervous cos of the 'bucketloads of low end' that you read about from the d12....
Title: Re: AKG D12 repair attempt...
Post by: wmb on October 26, 2010, 01:14:16 PM
(Question in last pragraph)

It's been a long time since I've logged in here but a search brought me back and boy am I glad. This is a fascinating thread! I was auditioning a new bass amp in my studio this weekend when I decided to try my D12 on the cabinet. I couldn't find my trusty D12 (with NOS capsule) which was mildly troubling but I have 3 more (long story) in various conditions so I just grabbed the one I knew to be my 2nd favorite (usually it mic's the low rotor of my 147 cabinet). On the bass cab the mids were stupendous and the lows were ok but it seemed to have a little bit of buzz or distortion that I don't get when I use it on the leslie. This got me concerned and thinking.

I remembered where my favorite D12 had been placed and I put it on the stand to replace the other. The distortion/buzz was not present. Hmmmm. So here I am after some searches.

The medium version of the story of how I got 4 goes something like this. I bought one (AKG, plastic frame) and then got an opportunity to buy 3 more of unknown working order for pretty cheap so I did. The other three were not badged AKG, they are branded L.I.A.R.E. and I think they say Italy on them as well. They all have metal frames and instead of having felt covering the capsule it is a fine screen. I don't think they are knock-offs because everything about the capsules and other internals look identical all the D12 photos I've seen and the capsule cover looks like those at this site http://www.avatarzenekar.hu/files/d12/ (http://www.avatarzenekar.hu/files/d12/). My LIARE D12's all measure approximately 50 Ohms. None have transformers.

Of the three LIARE mics one is clearly the best sounding but with the slight buzz noted above, the second has some hum and the back cover is really trashed and barely stays on the mic, the third and weakest (practically not working) is also in decent cosmetic condition. My original intent was to try and track down the buzz in mic (#1) and then that migrated into consolidating the more trashed mic (#2) that sounded okay into the casing of the good looking but poor performing #3.

After finding this thread I decided to change course and see if I could get mic #3 to work better and then possibly work my way through all three mic's to see if there is life in all of them yet. Where can I find this sweep test procedure outlined? Searches were not fruitful. Is it just connecting the mic connector to a headphone out and slowly turn up till it becomes audible like a tiny speaker?

Thanks for all the info in this thread

Billy B
Title: Re: AKG D12 repair attempt...
Post by: Biasrocks on October 26, 2010, 01:53:28 PM
Hey guys,

I've got a D12 here that's exhibiting some issues with high SPL applications.

Notably the bottom end folds up when using it inside of a kick drum. Top end
stays intact but nothing from about 500hz down.

The mic sounds fine in front of my Ampeg B15. But in the kick it's shutting down.

Curious, if anyone has had a similar issue.

I've read earlier about keeping the tension on the capsule screws relatively light so I've
only tightened them with a light tension. Should I try increasing the tension on
those guys to see if I can get a proper response on the kick?

Mark
Title: Re: AKG D12 repair attempt...
Post by: s2udio on October 26, 2010, 02:33:15 PM
You need to take it apart.....see page 1 and read again ? its all there
If the diapghams knackered ..no DC res after CLOSE inspection ,then it,s probably game over.
The signal sweep method "re rodabods post " is described here......seek and find !

I just wanted to say a big thanks for this thread.

I've just serviced one of these that was covered in black dust, and the photos were a great help in getting it going again.

THANKS!
Glad to help....esspecialy a mic expert like yourself
Title: Re: AKG D12 repair attempt...
Post by: wmb on October 26, 2010, 04:03:11 PM

The signal sweep method "re rodabods post " is described here......seek and find !



If you are referring to the second post in the thread then I found that right away. I was just looking for a little more detail. It must not be that harrowing since the descriptions are so light. I think the thing that got me worried was one post mentioning a tube powered signal generator. I will wing it with super low volume from a headphone jack working my way up and see what happens. The mic barely worked anyway.
Title: Re: AKG D12 repair attempt...
Post by: s2udio on October 26, 2010, 05:06:40 PM
Just hook it up to the output leads of the mic........ green/blue
The output impedance dont really matter...as long as you can get it to
oscilate......I used the headphone output of my laptop with software sig gen
Just start with the output gain very low at 1khz ,and increase untill it gently sings
Then sweep from 50 to -5k listening for any nastys...
Title: Re: AKG D12 repair attempt...
Post by: andre tchmil on October 26, 2010, 06:12:15 PM
If anyone ever wants to part with a membrane for a D12, let me know;
I have a complete mic except for this part.

thanks
Title: Re: AKG D12 repair attempt...
Post by: wmb on October 27, 2010, 12:17:37 AM
Any suggestions for separating the spacers. I think I need to re-order them. After rebuilding two capsules one of them is still pretty thin sounding at least when connect it to a mic pre. I've gathered that raising the membrane will increase the fullness.  The upside is that it barely worked at all before and now it produces a pretty strong signal.

I haven't rebuilt the whole mic yet and it's still just the capsule with the bass chamber. One thing about this particular capsule is the gasket on the back for the bass chamber is pretty dry and crumbly. I'm wondering if that could effect the bass response because otherwise the signal playback seem okay when I run the sweep through it.

Another thing, do the nasties sound really obvious? My sweeps have a slight buzzy quality but it's the whole sweep. I think I have heard a little momentary rasp before but there's was nothing standing out. I'm just trying to avoid having to tear it all down again.

Thanks

(P.S. I was kind of overwhelmed when I was removing screws placed some 40-50 years ago that the last person to do this was working as carefully as I was to accomplish the same goal, make a well performing mic.)
Title: Re: AKG D12 repair attempt...
Post by: wmb on October 27, 2010, 06:33:34 AM
My sine wave sweep after a tear down and cleaning. Here's a video. I have no idea if I have improved it or not.

http://lovelessmotel.com/d12/d12_sweep.3gp (http://lovelessmotel.com/d12/d12_sweep.3gp)
Title: Re: AKG D12 repair attempt...
Post by: MagnetoSound on October 27, 2010, 01:48:12 PM

Sounds like you're driving it hard! Does that distortion go away if you drop the level from the generator?

Title: Re: AKG D12 repair attempt...
Post by: wmb on October 28, 2010, 03:54:23 AM
I'll have to give that a try. I started out really low and it was kind of hard to tell how much LF was coming from such a tiny resonator. One post here mentioned it singing so I pushed it up a little more till I could hear it. I've spoken into the capsule with the green and blue wires connected crudely to a mic cable and the sound wasn't bad. Putting the bass chamber on really made a huge difference. I put this mic back into the shockmount before leaving the studio last night but didn't put a new end on the cable I had recently shortened.

Title: Re: AKG D12 repair attempt...
Post by: wmb on October 28, 2010, 11:51:11 PM
I am in a freakin' spot! >:( I've rebuilt two D-12's and they are generally improved quite a bit with the exception of some fizz at the upper mids and higher frequencies (>5k when recording electric bass). I don't know how to get rid of it. The membrane looked fine on both. The spacers on my capsules were pretty much fused together and I cannot separate them or move the the membrane around at all. In fact the spacers fit very snuggly between the three screws that stick up from the main body of the capsule. I'm not sure what to do to move the membrane around to position the coil in the gap more precisely. Any ideas?

The most frustrating part is how awesome the mids are for recording bass. Nice and aggressive and no tubby quality in the bass. These mics are very old versions with a metal frame.

Thanks.

BB
Title: Re: AKG D12 repair attempt...
Post by: clintrubber on January 28, 2011, 11:53:54 AM
Hello,

Just wondering, has anyone experience with the budget-line AKG D11 ?  (also called D11XLR).
So not the D112, but this beast:

(http://www.akg.com/mediendatenbank2/pspic/image/28/image1108478070_d11421208763b187.JPG)


Have already 12(E), 421, 441 for bass-cabs, but you all know how this goes, was nevertheless wondering if the D11 could be fun to add.

They're going cheap, seem well made and as it seems they're having a different signature
than the usual (...) 'low-mics'.

Brighter, less proximity, maybe even to the extend that it's puzzling why
AKG called this a bass-mic ;-)

(http://www.akg.com/mediendatenbank2/pspic/image/53/image1115733669_d114280bea5b3067.JPG)

http://www.akg.com/mediendatenbank2/pspic/hires/95/d114280bea5b3067.jpg (http://www.akg.com/mediendatenbank2/pspic/hires/95/d114280bea5b3067.jpg)


Thanks !
Title: Re: AKG D12 repair attempt...
Post by: nashkato on January 31, 2011, 08:26:06 AM
hi
opened up a D12/HI yesterday .
i didn't find any information on this one.
AKG manuals mention a D12/HIT but not a word about this HI.
capsule DCresistance is 50 ohm . there appears to be a transformer inside the basschamber : output DCresistance is 1K2 ohm.

in fact i only gave it a short try inspired by this thread.
i didn't have any luck moving the diaphragm by just loosening the srews and opened it up.
what can i say : it still works  ;)
i'll report back about further attempts, right now it goes on the shelve.

ps: how did you manage to put back on the spring-metalsheet , that keeps together the caspule and the chamber ?
      had more problems doing that than any of the re-assembling of the diaphragm, etc.
Title: Re: AKG D12 repair attempt...
Post by: poctop on May 27, 2011, 03:50:06 PM
Man i have done the whole thing and i found a micro clover inside the confined space life find always its way,
Dany
Title: Re: AKG D12 repair attempt...
Post by: zebra50 on May 27, 2011, 04:01:05 PM
You found a plant inside your mic??  :o

Normally I just find insects...

http://xaudiaelektrik.blogspot.com/2011/04/strange-things-you-find-inside.html

Maybe the insect left it there? Pictures please!
Title: Re: AKG D12 repair attempt...
Post by: poctop on May 28, 2011, 11:50:58 AM
I really wish i could take a picture of some quality to show but anyway i kept the particule it looks definitelvely vegetal to me it is still a greenish color and make some little cup shape form like a clover ,    interessting your article about the wierd things in mike.

hope the mike works for another 20 years now !

Cheers Mate,
Dany,
Title: Re: AKG D12 repair attempt...
Post by: archieaa1 on September 16, 2011, 07:59:25 PM
Hello Everyone

I read the post and pulled out my old thin sounding D12E. Moving slowly I pulled it apart, cleaned it up, and put it back together. Drum roll please...... It worked! It sounds good. I have 2- d12s and 2 D112 mics. Tested on my voice the repaired D12E seemed to have as much or maybe a little more low end than the d112. The big difference was the mids. The d12 had them and the d112 didn't. The interesting thing is the difference between the D12s. The one I repaired is a d12e with a black plastic frame and no transformer. The other D12 is a D12ES with a grey plastic frame and a transformer. I find that the mids and up sound quite the same but the older D12ES is some what weaker in the low end. Is this normal or does the older one need some attention as well? Has anybody else been able to compare the older to the newer?

Thanks for any info.

Archie
Title: Re: AKG D12 repair attempt...
Post by: Shuggie101 on June 30, 2012, 11:34:09 AM
Hi everybody

Sorry to dig up such an old thread but I just wanted to say a big thanks to everybody who contributed such useful advice.

I just followed he guidelines to re-build the AKG D25 that has been sitting unused in the bottom of my mic cupboard for a decade or more.

The sound started out thin, strangely coloured and, of course, totally lacking in bass. Now it sounds huge, detailed and surprisingly bright. I'm even liking it on acoustic guitar.

Mine has a transformer mounted in the bass chamber. I think it had previously been messed around with and since I'd be unlikely to use the bass roll off switching, I bypassed the switch and transformer.

Mine is a 50 Ohm D25 so I'm running the mic through the same Sowter transformer (50:200) that I use for my Reslo ribbon.

Now if anybody out there knows where to get a replacement suspension rubber - or how to make one - I'd love to know.

Thanks again

Shuggie

Title: Re: AKG D12 repair attempt...
Post by: s2udio on July 04, 2012, 04:34:06 PM
Well done on the repair
 ;)
As for the ""new"" on the old D series AKG's,...Unicorns come to mind !
Use your ingenuity,....modern foams come to mind ?
Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on October 31, 2012, 03:07:49 PM
If no one minds I think I'll keep this thread alive.

I have two d12s here in need of diaphragms.
Title: Re: AKG D12 repair attempt...
Post by: s2udio on October 31, 2012, 04:10:21 PM

Unobtanium  Unfortunately....... :(

Have the windings gone OC ?

Hopefully someone will one day make a few DIY  D12 replacement diaphragms ... £100 each must be worth it ?

Maybe an opening for for someone with the time and patience, passion, jigs and eyes to perfect.

But I don't hold a lot of hope now AKG have a released the new version.

What have AKG come up with ?, a chinese miracle !

Must try one against my two working originals , well after all the D12 , the definitive no contest  Kick  mic,

In my ears anyway.

Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on October 31, 2012, 06:00:44 PM
No, the mics are perfect except the fine wires from the coil have perished.
The tail ends that enter the capsule are intact.


I kinda thought that myself. Surely someone somewhere has the capability to manufacture these?
Since we're making it up though, why not start at £30? :p

Incidentally, were there variations? I'm fairly sure the coil size is different between my two broken D12s.
Title: Re: AKG D12 repair attempt...
Post by: s2udio on November 01, 2012, 06:56:52 AM
No, the mics are perfect except the fine wires from the coil have perished.
The tail ends that enter the capsule are intact.

Then maybe a carefully exercised repair may be possible.
Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on November 01, 2012, 09:33:04 AM
Nah, I don't see it.
The wires are broken right at the coil.

Thanks though.
Title: Re: AKG D12 repair attempt...
Post by: pan60 on November 01, 2012, 12:46:30 PM
Nah, I don't see it.
The wires are broken right at the coil.

Thanks though.
I have bee looking for a few of these for dissection, if you are interested in parting with them p.m. me.
pan
Title: Re: AKG D12 repair attempt...
Post by: bkbirge on November 01, 2012, 01:17:36 PM
Nah, I don't see it.
The wires are broken right at the coil.

Thanks though.

Post pics, you never know, someone may see a way to get 'em working again.
Title: Re: AKG D12 repair attempt...
Post by: nashkato on November 02, 2012, 09:17:21 AM
i managed to repair a tweeter lately .(original ones unobtainable and no after market ones either ).fortunately one of the wires was broken right at the coil , ... a steady hand , being able to see good at short distances , ( or a magnifying glass) , tiny tools , and you go .
one winding less makes no difference , at least to my ears and at a tweeter.
sure , the coil of a D12 is quite smaller ,... but may be possible to do
Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on November 02, 2012, 09:27:27 PM
Good info there! Thanks.

Is there a list anywhere of other mics they used the d12 diapragm in?
Perhaps there are cheaper mics which be bought for the part?
Title: Re: AKG D12 repair attempt...
Post by: s2udio on November 03, 2012, 08:47:09 AM
the coil of a D12 is quite smaller ,... but may be possible to do

It is possible

Perhaps there are cheaper mics which be bought for the part?

Extremely unlikely......in fact i would go as far as to say,  Nope

Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on November 08, 2012, 10:39:41 AM
My d12 membranes are beyond repair, but.............

I had a 57 where the glue had dried up and the membrane was loose.
In the repair attempt, the coil wires snapped very easily.

So, a 57...who cares right?why not have a butchers.

The coil is glued to the membrane in spots, but the membrane is how would you say, corrugated? There are gaps between the coil and membrane at points.

This made it easy to completely remove the coil, tease out the wire ends, then glue it back in place.

It worked. OK, it sounds a little dull because I was too liberal with the glue, but it worked.
It made me think how hard could it be to just make diaphragms and coils?

I figure a mould can be taken of an old membrane, a new one pressed (from the right material), a coil wound, and glued in place. Simples, right?

I failed to remove my d12 coils from the diaphragms, but if anyone manages this then it's even easier. You just gota wind a new coil and glue it in place.

My thought is I could probably do this, but badly, so surely someone here can do it well?

Thoughts?
Title: Re: AKG D12 repair attempt...
Post by: MagnetoSound on November 08, 2012, 01:31:05 PM
My thought is I could probably do this, but badly, so surely someone here can do it well?

That's a fine piece of logic, if ever I heard one.  ;D

Title: Re: AKG D12 repair attempt...
Post by: CJ on November 08, 2012, 03:57:18 PM
if you rip the tranny out of the 57 you will have the killer bass drum mic,

when used in conjunction with a speaker mic of course,

ask the Soundguy,

what happened to SSLKeef? is he the Drip guy?

dude said he was gonna meet me at SFO one time, flakester,  :o

i think Scenaria got locked up for something, or OD'ed on Red Bull,

does anybody have some Stephen Paul matched KM84's for sale?

Tony, where is that new mic?
Title: Re: AKG D12 repair attempt...
Post by: MicDaddy on November 08, 2012, 08:03:16 PM
Quote
My thought is I could probably do this, but badly, so surely someone here can do it well?

I have extensive experience doing exactly this and I've been begging for a machinist for a couple of years now... bring back Lou Burroughs

The detail needs to be absolutely precise, the diaphragm flutes are very very important. 

The tooling requirement is so niche and small scale in nature there doesn't seem to be much interest in the job.  Perhaps the skill required is upper echelon stuff?  I don't know, I'm not a machinist. 

Unfortunately unless you are the machinist this is going to be cost inhibitive.  I've considered yet to have found a local foundry DIY or otherwise willing to give investment casting a try.

steenamaroo had a good idea of trying to track down an existing coil/diaphragm assembly.  There's no reason it wouldn't 'work' so long as the coil lives comfortably within the gap.  Then again this is not going to be the same as if it had the proper assembly.





Title: Re: AKG D12 repair attempt...
Post by: CJ on November 09, 2012, 04:37:12 AM
does the shure b52 kick mic have all these problems? jus sayin...
Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on November 10, 2012, 08:58:28 PM
Nope, but is it a d12? :p
Title: Re: AKG D12 repair attempt...
Post by: CJ on November 11, 2012, 01:20:14 AM
nope, but i hear it has good rejection for live use,
Title: Re: AKG D12 repair attempt...
Post by: MicDaddy on November 11, 2012, 09:43:54 AM
since we're off on this tangent, I happen to like the beta 52a a lot, I prefer the attack/click it gives for live rock/metal.  It's not a bad mic for recording either.
Title: Re: AKG D12 repair attempt...
Post by: Biasrocks on November 11, 2012, 11:13:26 AM
since we're off on this tangent, I happen to like the beta 52a a lot, I prefer the attack/click it gives for live rock/metal.  It's not a bad mic for recording either.

RE20, M88, D25, D12 all get kick duty around here. They all sound different but they all take EQ well. I don't find that to be the case with more modern types, you're generally stuck with what they give you.

For example, I've got a D112 that rarely sees the light of day, in fact I don't think I've used it in over ten years.

Regards,
Mark
Title: Re: AKG D12 repair attempt...
Post by: CJ on November 11, 2012, 02:43:05 PM
anything but the Audix d6, the music stor guy calls it the Dog 6, waht up,

Title: Re: AKG D12 repair attempt...
Post by: MicDaddy on November 11, 2012, 02:51:39 PM
don't find that to be the case with more modern types, you're generally stuck with what they give you.

Agreed, sometimes it's just what the gig calls for, and in a pinch for time the 'tuned' mics are quick and easy.  I know what I'll get if I throw up a 52a. 

It hasn't been mentioned but the EV 868 is a badass kick mic as well.  I don't care much for the D112.
Title: Re: AKG D12 repair attempt...
Post by: CJ on November 11, 2012, 04:32:48 PM
ok so where do you put the condenser/fet mic when doing the 2 mic thing?

seems like it would blow up if too close and get too much bleed if it were to far, wtf, over?  :-\

Title: Re: AKG D12 repair attempt...
Post by: MicDaddy on November 11, 2012, 04:36:16 PM
When I get the FET47 built I'm going to put it right up onto the resonating head.
Title: Re: AKG D12 repair attempt...
Post by: CJ on November 11, 2012, 04:53:20 PM
wow, need a tight capsule for that,



i also like the sm7b

here is a pretty cool kic mic shootout>

http://www.youtube.com/watch?v=Ki3UtgNR4C0
Title: Re: AKG D12 repair attempt...
Post by: Biasrocks on November 11, 2012, 06:54:06 PM
wow, need a tight capsule for that,



i also like the sm7b

here is a pretty cool kic mic shootout>

http://www.youtube.com/watch?v=Ki3UtgNR4C0

Yep, 47fet is super cardioid.

As for placement, hold the back of your hand near the skin as the drummer hits, place the mic where the most air is moving. Building a tent with Packing blankets help with leakage.

Regards,
Mark
Title: Re: AKG D12 repair attempt...
Post by: CJ on November 12, 2012, 03:37:32 PM
Dave Grohl technique>

Title: Re: AKG D12 repair attempt...
Post by: MicDaddy on November 22, 2012, 11:06:10 PM
Hey everybody,  anybody with a D12 care to confirm some measurements for me?  As close to .xxx as possible

-OD voice coil
-ID voice coil
-gap width
-confirm if coil leads are dressed 'on top' or 'under' diaphragm?
-awg magnet wire
-material: copper, alum, etc..
-# of turns per layer
-# of layers

Any dead, open coil diaphragms would help if anyone cares to donate.  If they are distorted, dented, rounded flutes, or other than perfect disregard.

Title: Re: AKG D12 repair attempt...
Post by: pan60 on November 23, 2012, 01:12:40 PM
Hey everybody,  anybody with a D12 care to confirm some measurements for me?  As close to .xxx as possible

-OD voice coil
-ID voice coil
-gap width
-confirm if coil leads are dressed 'on top' or 'under' diaphragm?
-awg magnet wire
-material: copper, alum, etc..
-# of turns per layer
-# of layers

Any dead, open coil diaphragms would help if anyone cares to donate.  If they are distorted, dented, rounded flutes, or other than perfect disregard.

LOL
we think to much alike!

Title: Re: AKG D12 repair attempt...
Post by: steenamaroo on July 06, 2013, 11:34:22 AM
Hey everybody,  anybody with a D12 care to confirm some measurements for me?  As close to .xxx as possible

-OD voice coil
-ID voice coil
-gap width
-confirm if coil leads are dressed 'on top' or 'under' diaphragm?
-awg magnet wire
-material: copper, alum, etc..
-# of turns per layer
-# of layers

Any dead, open coil diaphragms would help if anyone cares to donate.  If they are distorted, dented, rounded flutes, or other than perfect disregard.

Did you have any success in gathering this info?
Title: Re: AKG D12 repair attempt...
Post by: dmp on March 12, 2015, 11:00:42 AM
Bumping this great thread - my D12e lost the low end a few weeks ago.
Used a signal generator, loosened the 6 screws in the clamping ring, and was able to slightly realign the diaphragm following the advice in this thread.
The mic is back to 100% now.
Thanks group diy

 
Title: Re: AKG D12 repair attempt...
Post by: juneaudio on March 09, 2019, 01:04:43 AM
I have a D12 in need of repair.  I think I could gather the info I need but none of the old pictures in this thread are there anymore.  Can anyone help me out?

Title: Re: AKG D12 repair attempt...
Post by: OneRoomStudios on March 15, 2019, 06:11:00 PM
 ;)

https://web.archive.org/web/20150319144657/http://groupdiy.com/index.php?topic=33755.40
Title: Re: AKG D12 repair attempt...
Post by: OneRoomStudios on March 29, 2019, 04:08:11 PM
I did two of these repairs recently. Both were successful - one note though. Don't just concentrate on the low frequencies when tuning the diaphragm placement. I ended having one with plenty of low-end, but missing upper-mids until I re-seat it slightly while listening to 3Khz.
Title: Re: AKG D12 repair attempt...
Post by: s2udio on March 30, 2019, 04:30:58 AM
Wow, thanks OneRoomStudios for putting that link up........I have recently found the original images of the D12 strip on an old Drive. They can be zoomed for greater clarity.
I can zip them up for anyone interested, or if someone wants to host them be my guest.
10 years ago.......... really !!  :o

Title: Re: AKG D12 repair attempt...
Post by: stereokiller on April 26, 2019, 09:18:23 AM
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.
Title: Re: AKG D12 repair attempt...
Post by: alhe on April 27, 2019, 11:19:06 AM
As someone who has repaired several old AKG's, I can confirm that changing the position of the paper shims helps in some cases. I have seen the geometry of the diaphragm change in some cases (it sinks down, pulled under by its own weight). So, moving a shim helps to lift up the voice coil. Not recommended unless something is notably wrong simply because of how fragile the wiring is. Another trick I learned is to clean the diaphragm with a small magnet (an alnico guitar pickup magnet works great) if there are any magnetic particles caught on the diaphragm.
Title: Re: AKG D12 repair attempt...
Post by: chops on April 28, 2019, 11:22:29 AM
As someone who has repaired several old AKG's, I can confirm that changing the position of the paper shims helps in some cases. I have seen the geometry of the diaphragm change in some cases (it sinks down, pulled under by its own weight). So, moving a shim helps to lift up the voice coil. Not recommended unless something is notably wrong simply because of how fragile the wiring is. Another trick I learned is to clean the diaphragm with a small magnet (an alnico guitar pickup magnet works great) if there are any magnetic particles caught on the diaphragm.

Can you die scribe this procedure in more detail?  I’m always worried about getting pulled in by the voice coil magnet and denting/damaging the diaphragm...
Title: Re: AKG D12 repair attempt...
Post by: alhe on April 29, 2019, 03:54:35 AM
I have used to lean the bar magnet against the side of the motor assembly. That way the magnet is anchored and don't slip that easily. Never damaged a diaphragm using this method but there is always a risk in doing so, so be careful.
Title: Re: AKG D12 repair attempt...
Post by: panman on May 01, 2019, 08:32:37 PM
As someone who has repaired several old AKG's, I can confirm that changing the position of the paper shims helps in some cases. I have seen the geometry of the diaphragm change in some cases (it sinks down, pulled under by its own weight). So, moving a shim helps to lift up the voice coil. Not recommended unless something is notably wrong simply because of how fragile the wiring is. Another trick I learned is to clean the diaphragm with a small magnet (an alnico guitar pickup magnet works great) if there are any magnetic particles caught on the diaphragm.

First of all, the diaphragm does not "sink down,pulled under by it`s own weight". It becomes concave because of the iron dust and debris gathering around the dome. Due to the size of the magnet, it has a bigger than normal a pull and attracts the iron particles from the surroundings, but also from the mic itself, because of the corrosion. So the more debris, the more bass is lost and the more deformation is taking place and in the end the voice coil cannot move freely. A jamming voice-coil is the result.
Once that happens, it is a case for an experienced professional.

Now, if there are only a few tiny iron particles around the dome and no deforming has taken place yet, then just cleaning them away might get you the original sound back. Unfortunately, this is most likely not the case. Why? The oldest D12:s are more than 60 years old and even the reissue capsules are 22 years old already. In most cases the iron dust/debris has been gathering on top of the diaphragm for decades and was never cleaned off. And those iron particles are never spread evenly around the dome and so the deforming also never is even.  So, lifting the diaphragm higher does very seldom help. It may give you some bass back, but it won`t sound correct in the mids and highs. It will sound "honky".

Cleaning the iron debris with a magnet is too dangerous. So, that is a no go. The capsule magnet has an enormous pull and would be amplified by the magnet brought close to it. One careless slip and you can say goodbye to the diaphragm. And unfortunately only a perfect diaphragm is going to sound right. A much safer way is to use a very thin and small-tipped screwdriver, that is magnetic, because there would be a weaker pull all in all, but yet enough pull to pick each tiny particle individually away. Even then, you need to be very carefull not to let the screwdriver slip and damage the diaphragm. Actually, that should only be done by a very experienced a person, but I do not wish to discourage anybody. After all, there is no other way of learning, than doing it. After some ten or fifteen spoiled diaphragms and broken coil ends, it tends to give somewhat a better outcome.

There are much more problems, that need to be addressed, if you want to get the sound to specs.  Some of those have been mentioned in the threads here, but too many are not, because earnestly, they can only be performed by an experienced professional(with D12:s!).





Title: Re: AKG D12 repair attempt...
Post by: 12afael on May 02, 2019, 07:14:13 AM
I have had success taking iron particles from a mic using masking tape. I´m not saying stick the tape to the diaphragm but lift the particles with a corner of the tape.  Of course it depend of how strong the magnet is. Trying to move those particles with a screwdriver or something that will be attracted is not a good idea.

masking tape is used to clean magnet in speakers before reconing.
Title: Re: AKG D12 repair attempt...
Post by: panman on May 02, 2019, 05:33:54 PM
I have had success taking iron particles from a mic using masking tape. I´m not saying stick the tape to the diaphragm but lift the particles with a corner of the tape.  Of course it depend of how strong the magnet is. Trying to move those particles with a screwdriver or something that will be attracted is not a good idea.

masking tape is used to clean magnet in speakers before reconing.

Sure you can use masking tape or even gaffa. Just, that in most cases it does not work too good for me. The iron dust often is sticking and don`t forget, that there is the magnet pull to overcome.  Now, I use the small-tipped screwdriver method, but if you read what I wrote, it should be clear, that I did not recommend it to anybody else, except a professional, who has lots of experience repairing D12-family mics. Hope its more clear now. Besides, in most cases, cleaning the diaphragm or/and lifting it higher will not bring you the original sound back. Neither will that frequency sweep do that. Much more is needed and that is skills and experience earned with years of hard work and devotion. Trying to repair a D12 is full of traps, that you need to know,
but cannot know doing it the first time. Maybe not even the following few times. So it is easy to destroy your mic beyond repair, but learning by doing is the only way, if that is what you want. Do it by all means, but be realistic about the outcome!



Title: Re: AKG D12 repair attempt...
Post by: alhe on May 03, 2019, 05:58:50 AM
First of all, the diaphragm does not "sink down,pulled under by it`s own weight". It becomes concave because of the iron dust and debris gathering around the dome.

I do not disagree with you. We are essentially saying the same thing.

I think it's wise to not encourage forum members to attempt a potentially unsuccessful repair. Then again, there are not many professional techs with lots of experience on working on these old AKG’s. If you can get in touch with one locally, then great. I am only sharing my experiences as it has helped me in the past, on the assumption that people here might have some experience with working on old dynamics and fine electronics in general. I'll reinstate that it requires great care to work on old AKG’s. I have saved a handful of these if we also count the D19 and the D119, which all uses the same diaphragm.
Title: Re: AKG D12 repair attempt...
Post by: panman on May 06, 2019, 05:53:26 AM
if we also count the D19 and the D119, which all uses the same diaphragm.

A little correction needs to be added here. Yes, D19C, D19E, D24 and D119 use the same transparent diaphragm, but D19B models have a differend diaphragm blue or blueish in color. Just to avoid any confusion, it needs to be added that D12 family mics do not have any of those. Well ok, as it so often is the case(with AKG), there is an exception, if we include the D17 into the D12-family. D17 also has the "same" blue diaphragm as the D19B. "Same" here too is somewhat debatable, but I`ll leave it at that, because this thread is about D12.
Title: Re: AKG D12 repair attempt...
Post by: jordan s on May 16, 2019, 11:08:25 PM
I broke off the brittle leads coming off the diaphragm when I attempted to repair mine. Any way back from that?
Title: Re: AKG D12 repair attempt...
Post by: panman on May 17, 2019, 06:08:26 AM
I broke off the brittle leads coming off the diaphragm when I attempted to repair mine. Any way back from that?

Yes, a very experienced expert in fixing D12:s may still be able to repair it.