repairing a dynamic mic (a guide)

[12afael]

I'm repairing an old MUST UD-402 rare japanese microphone that I bought in a flee market.  I thought I could do a post to share some ideas.

The capsule was crushed, I repaired the membrane with some hot glue time ago. if you put a very small drop gently on the membrane and retire quickly the gluegun you will end with a very fine glue string that you can use to pull the membrane. To remove the glue you can twist the glue drop near the membrane it should come off smoothly.

This technique work well but can't repair the wrinkles on the membrane, maybe a hot gun could release the tension on the membrane. I haven't tried and it could be dangerous for the membrane.
maybe it could be used to repair speakers domes too.

I did this on this mic a year ago ,I took some pictures but I don't know where are now...

anyway... today I'm repairing the coil. it was split as can be seen on the picture.

I did a small ring of paper to pull the coil down I have steady hand but this is a very delicated process and the paper ring will produce a less strong force over the coil and also can reduce the variations of pressure of my hand.

I did use super glue to re bond the coil and I needed a small brush. I didn't had one near so I built one with my own hair.  the super glue dry fast on it but it was a very quick aplication.  you don't want to drop a big drop on the mebrane so the brush is essential.

here is a picture of the pressing process after the glue aplication

some masking tape is good to clean the capsule from dust or metal in the magnet.

the mic is now working it sound very vintage, I could have some use of it but not on everything.

cheers
Rafael

 

[LOmmPA]

Hello!

Finally I found a topic in this!

I have a BEAG D5 dynamic microphone, it is a Hungarian AKG D12 clone from the early '60. Its coil is broken but the membrane is fine. I tried to solder the connecting wires but it didn't help. Could you write me some tips/tricks? How can I measure the coil wire diameter and the coil diameter precisely?  Which method can be used for pick off the coil from the membrane and put the new one back on it?

Thanks!

Peter

(Attached a picture about the membrane and the coil)

 

[12afael]

I don´t have a definitive answer to this.  I´m far from an expert. I would try to measure the number of turns to determine the thickness of the cooper wire.  you willl need a lot of magnification.

I would try to use some kind of solvent to remove the coil but I would do some experimentation because some solvents could damage the the membrane.

how to put a new coil in the centre. I have no ideas at the moment. Maybe create a rig to hold the membrane in position while doing some acoustic test.

I have never done a coil for a mic. maybe I would try with a core of caramel to dissolve it later in water.  take out the coil from the form can be tricky.

I hope it help.