Author Topic: AKG D12 repair attempt...  (Read 28602 times)

SSLtech

  • Member
  • Posts: 5351
  • Florida (Formerly UK)
AKG D12 repair attempt...
« 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
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.


rodabod

  • Member
  • Posts: 2900
  • London
Re: AKG D12 repair attempt...
« Reply #1 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.
Quote from: tv
punchy fat bastard chip

MagnetoSound

  • Member
  • Posts: 1122
  • Southern England
    • Magneto Sound
Re: AKG D12 repair attempt...
« Reply #2 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!
« Last Edit: June 27, 2009, 01:36:07 PM by MagnetoSound »
Dan

I don't think people realize what an embarrassment of riches this place is. - Paul Gold

Rob Flinn

  • Member
  • Posts: 3083
  • Sussex, UK
Re: AKG D12 repair attempt...
« Reply #3 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.
regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........

SSLtech

  • Member
  • Posts: 5351
  • Florida (Formerly UK)
Re: AKG D12 repair attempt...
« Reply #4 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
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

SSLtech

  • Member
  • Posts: 5351
  • Florida (Formerly UK)
Re: AKG D12 repair attempt...
« Reply #5 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
« Last Edit: May 26, 2009, 04:28:09 PM by SSLtech »
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

SSLtech

  • Member
  • Posts: 5351
  • Florida (Formerly UK)
Re: AKG D12 repair attempt...
« Reply #6 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
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

Rob Flinn

  • Member
  • Posts: 3083
  • Sussex, UK
Re: AKG D12 repair attempt...
« Reply #7 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.
regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........

Sredna

  • Member
  • Posts: 872
  • Berlin, Germany
Re: AKG D12 repair attempt...
« Reply #8 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
Hmm... in which direction do the electrons actually go?

craptical

  • Member
  • Posts: 360
  • Malmo, Sweden
    • http://www.gulastudion.com
Re: AKG D12 repair attempt...
« Reply #9 on: May 27, 2009, 09:06:40 AM »
Suddenly it feels good to have kept the old capsules from our D12´s :)


rodabod

  • Member
  • Posts: 2900
  • London
Re: AKG D12 repair attempt...
« Reply #10 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.
Quote from: tv
punchy fat bastard chip

rodabod

  • Member
  • Posts: 2900
  • London
Re: AKG D12 repair attempt...
« Reply #11 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.
Quote from: tv
punchy fat bastard chip

SSLtech

  • Member
  • Posts: 5351
  • Florida (Formerly UK)
Re: AKG D12 repair attempt...
« Reply #12 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
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

Rob Flinn

  • Member
  • Posts: 3083
  • Sussex, UK
Re: AKG D12 repair attempt...
« Reply #13 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.
regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........

strangeandbouncy

  • Member
  • Posts: 2115
  • West Sussex. UK
Re: AKG D12 repair attempt...
« Reply #14 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
. . . . RUH ROH . . . . .

strangeandbouncy

  • Member
  • Posts: 2115
  • West Sussex. UK
Re: AKG D12 repair attempt...
« Reply #15 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
. . . . RUH ROH . . . . .

SSLtech

  • Member
  • Posts: 5351
  • Florida (Formerly UK)
Re: AKG D12 repair attempt...
« Reply #16 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
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

Rob Flinn

  • Member
  • Posts: 3083
  • Sussex, UK
Re: AKG D12 repair attempt...
« Reply #17 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
regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........

rodabod

  • Member
  • Posts: 2900
  • London
Re: AKG D12 repair attempt...
« Reply #18 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.
Quote from: tv
punchy fat bastard chip

eskimo

  • Member
  • Posts: 542
  • Sweden
Re: AKG D12 repair attempt...
« Reply #19 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?


 

Related Topics

  Subject / Started by Replies Last post
19 Replies
3915 Views
Last post June 18, 2006, 06:44:54 PM
by matta
8 Replies
2308 Views
Last post October 21, 2005, 08:59:08 PM
by bcarso
24 Replies
5351 Views
Last post April 24, 2006, 03:10:45 PM
by CJ
22 Replies
1911 Views
Last post October 13, 2009, 07:31:26 AM
by volker
14 Replies
2317 Views
Last post April 25, 2012, 09:31:30 AM
by etheory