AKG D320B repair

[f0m3]

Hey,
ich have a good conditioned AKG D320B with this problem:
It basically works but it sound as if there is a very high highpass and it has low volume.
There is a nice schematic to the mic here: http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/AKG%20D-320B%20Hypercardioid%20Dynamic%20Microphone.pdf

I already checked the built in bass rolloff switch by removing it from the mic and i bypassed the hum bucking coil with two crocos wich didnt have any effect. What leads me to the conclusion there might be something wrong with  that coil. Maybe a shorty?
When i measure the pure capsule without the humbucking coil i get 300 ohms, when i measure the humbucking coil i get about 10 ohms.

Any suggestions? it might be possible to handrewind the humbucking coil because its outside of the capsule...

 

[PRR]

> the pure capsule without the humbucking coil i get 300 ohms, when i measure the humbucking coil i get about 10 ohms.

With Bass switch FLAT?

With Bass in Cut1 or Cut2 you are measuring the bass-cut coil in parallel with the capsule. The bass-cut coil is likely to be 10 Ohms at zero frequency rising to >300 ohms by mid-bass.

Could the Bass Cut switch be busted inside so it always bass-cuts? (Does this part disconnect?)

 

[f0m3]

No,
i disconnected the bass-rolloff from the capsule. Its just the 3 solder pads 1,2,3 where is connected:
1: capsule internal coil +
2: capsule internal coil - AND humbucking coil +
3: humbucking coil -

between 1 and 2 i measured 300ohms
between 2 and 3 i get about 10 ohms
between 1 and 3 i get about 300+ ohms (both resistances in series)

When i bridge pin 2 and 3 and test the microphone without the bass rolloff-filter connected i get the same sound result as without the bridge. That made me suggest the humbucking coil might be shortet somehow.

 

[abbey road d enfer]

No,
i disconnected the bass-rolloff from the capsule. Its just the 3 solder pads 1,2,3 where is connected:
1: capsule internal coil +
2: capsule internal coil - AND humbucking coil +
3: humbucking coil -

between 1 and 2 i measured 300ohms
between 2 and 3 i get about 10 ohms
between 1 and 3 i get about 300+ ohms (both resistances in series)

When i bridge pin 2 and 3 and test the microphone without the bass rolloff-filter connected i get the same sound result as without the bridge. That made me suggest the humbucking coil might be shortet somehow.

Wrong conclusion IMO. All this seems correct to me.
Sounds like a dead capsule. I would not think they're available after all theses years, particularly with the Samsung acquisition and shut-down of the Austrian factory. However, you may find a suitable replacement capsule from Alibaba.
I recently bought a set of 4 SM57 replacement capsules for about $11, and they're almost undistinguishable from the real McCoy.

 

[f0m3]

So... you would say that the humbucking coil doesn't usually affect sound or volume? I only know humbuckers from electric guitar pickups and the sound and volume difference in this is huge!

 

[abbey road d enfer]

So... you would say that the humbucking coil doesn't usually affect sound or volume? I only know humbuckers from electric guitar pickups and the sound and volume difference in this is huge!

The humbucking effect in gtr p/u is based on two coils helping each other to deliver signal but fighting each other for unwanted signals.
In a mic, the humbucking coil delivers no signal, but fights hum.
So yes, the humbucking coil does not make a difference in terms of sensitivity.

 

[f0m3]

The humbucking effect in gtr p/u is based on two coils helping each other to deliver signal but fighting each other for unwanted signals.
In a mic, the humbucking coil delivers no signal, but fights hum.
So yes, the humbucking coil does not make a difference in terms of sensitivity.

Ok, i understand, sounds logically to me as i know that the humbucker in a guitar is part of the "pickup".

My other question is: Is it to expect that the humbucking coil has such a different resistance? I would have thought that a humbucking coil should have the same number of windings/impedance and so an equal or at least approximately equal amount of DC resistance.

 

[abbey road d enfer]

Ok, i understand, sounds logically to me as i know that the humbucker in a guitar is part of the "pickup".

My other question is: Is it to expect that the humbucking coil has such a different resistance? I would have thought that a humbucking coil should have the same number of windings/impedance and so an equal or at least approximately equal amount of DC resistance.

It's the surface that counts: the humbucking coil uses the full housing diameter, when the moving coil is about a half-inch. Also it is made of much thicker wire.

 

[panman]

It`s been really a long time since I have repaired D300-series mics. Not D320 though, but if i remember correct, they were D330.s.
The capsule is most likely the same in all D300-series mics and that is the standard capsule used in many others too. The problem with your mic is clearly the capsule. Either the coil is jamming and /or the diaphragm is dented and wrinkled, perhaps because someone tested it by blowing or whatever the reason. It may be repairable, but only by a person, who knows exactly what to do and how.

 

[f0m3]

Well, the mic is not good enough to engage a skilled person but maybe id try some by myself. The first point would be to remove the "hood" of the capsule to see if the membrane is damaged. It seems to be glued on would applying carefull heat be a way to remove the cap above the membrane?

 

[abbey road d enfer]

Well, the mic is not good enough to engage a skilled person but maybe id try some by myself. The first point would be to remove the "hood" of the capsule to see if the membrane is damaged. It seems to be glued on would applying carefull heat be a way to remove the cap above the membrane?

Thorouhly avoid heat at proximity of a dynamic capsule; the diaphragm may not survive and the body may warp.

 

[moamps]

Most probably the membrane in the capsule is jammed, from the top with small metallic/magnetic particles or from behind from unglued magnet pole piece. Sometimes the magnet itself falls apart.  Your chances to fix it are very slim. Good luck.
Btw,  you can test it by applying an audio signal to microphone from  headphone output of a smartphone or line out from a tuner or such source. You should hear a quiet sound from mike clear and in a full bandwidth.

 

[Whoops]

The capsule is shot! sorry