AKG D550 - no sound
- Thread starter Nelson Paschoal
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Help Support GroupDIY Audio Forum:
Check visually with a magnifier glass to see if any coil wire is broken, there should be 2 of them coming out of the diaphragm.
Try to see also if you get a sound straight from the capsule solder tabs instead of from the XLR connector, be careful not to break the thin coil wires that are connected to the solder tabs.
Try to see also if you get a sound straight from the capsule solder tabs instead of from the XLR connector, be careful not to break the thin coil wires that are connected to the solder tabs.
Nelson Paschoal
Active member
Hello friend, I´ve tested directly in the tabs with a scope, but not a single wave came out, and if there are a broken coil maybe the resistence should be infinite, right?
panman
Well-known member
No, not in the case you only have measured the humbucking-coil and not the voice-coil.
Nelson Paschoal
Active member
I don´t get it, there are two coils in this mic? What I have to do to know if this mic is working?
There could be yes.
panman
Well-known member
No offence, but if you don`t even know what a "humbucking coil" is, how do you expect to be able to fix that microphone? I mean, you should have some basic knowledge of dynamic microphones to start with. The voice coil is attached to the diaphragm and moves with it. Many Dynamic mics have a humbucking coil, but not all. It is the second coil wound the opposite direction from the voice coil meant to do what the name says. It does not move. It can be around the capsule or after the capsule or on top of it. Usually a lot less windings from the voice coil. So it would only measure a few ohms. It is connected in series with the voice coil.
To start with, you already know the mic does not work (no sound). I have a very good idea how the dynamic mics work (and don`t), but I don`t know this mic in question. Nevertheless, the first thing to check is if the XLR has proper connections. You can measure between pins 2 and 3 and there should be a reading. If no reading, take out the XLR and check that the wires are not broken or loose. Often the mics have a step-up trafo and then it only reads the secondary winding, which is mayby 50-60ohms. If no trafo, then it should read 200+something ohms(the voice coil is then ok). However, if there is a trafo, and you measure from the primary-side, you only get something like you did get(12.6 ohms), because the voice-coil-(humbucking-coil) is parallel with the primary. This may be the case here. There is also a chance, that the voice-coil is open, but you somehow managed to measure the HB-coil and get that reading. Normally the HB-coil reads les than 10 ohms though. To measure the voice-coil properly you need to disconnect one end from the primary. Then the VC should read 10-60 ohms and without a trafo it should read c. 200 ohms.
Sorry to write a long explanation, but writing is not my best virtue. So, at least in theory, your voice-coil may be ok, if you measured 12,6 ohms, but you better know how the wiring goes. This is what I can say without having the mic taken apart in front of me or seeing the schematics.
Hope this helps!
To start with, you already know the mic does not work (no sound). I have a very good idea how the dynamic mics work (and don`t), but I don`t know this mic in question. Nevertheless, the first thing to check is if the XLR has proper connections. You can measure between pins 2 and 3 and there should be a reading. If no reading, take out the XLR and check that the wires are not broken or loose. Often the mics have a step-up trafo and then it only reads the secondary winding, which is mayby 50-60ohms. If no trafo, then it should read 200+something ohms(the voice coil is then ok). However, if there is a trafo, and you measure from the primary-side, you only get something like you did get(12.6 ohms), because the voice-coil-(humbucking-coil) is parallel with the primary. This may be the case here. There is also a chance, that the voice-coil is open, but you somehow managed to measure the HB-coil and get that reading. Normally the HB-coil reads les than 10 ohms though. To measure the voice-coil properly you need to disconnect one end from the primary. Then the VC should read 10-60 ohms and without a trafo it should read c. 200 ohms.
Sorry to write a long explanation, but writing is not my best virtue. So, at least in theory, your voice-coil may be ok, if you measured 12,6 ohms, but you better know how the wiring goes. This is what I can say without having the mic taken apart in front of me or seeing the schematics.
Hope this helps!
Nelson Paschoal
Active member
No offence at all, and you right I really know nothing about dynamic mics but I really want to fix it, your explanation opens my mind, I will study more about dynamic mics and everything you wrote. I´ll check if this mic have a transformer, I suspect that don´t, it´s a light mic, but I do it. Thanks!!!
Also to study also what is the hum-bucking coil, search pictures of the sennheiser MD421 mics capsule, the humbucking coil is the coild on top, on top of the diaphragm in this specific mic and its really easy to see
Nelson Paschoal
Active member
Yesterday I checked again the mic, it doesn´t have a transformer, but I noticed that there are 3 pads, one without any connection and two connected to the coil (I can´t say which) visible in the 3rd pic I posted, this pad have no measure with the the other two pads, but I know that there´s something about it.
panman
Well-known member
The third pic shows the humbucking coil on top of the capsule. So, that`s what you have been measuring. It seems the voice coil is shot and I cannot see any way that you would be able to fix it, because that would require removing the diaphragm. That may not even be possible without destroying it. As I said before, I don`t know this mic, but you can try anyway, because as the mic is now, it is not likely to have any value and you don`t have much to loose. Whatever the outcome, you end up knowing a bit more about dynamic mics.
