MD441 Repair Help

[Sredna]

@Rossi:  PMd!

 

[MicDaddy]

Rossi,

It sounds like you are removing the entire faceplate/resonator & coil diaphragm from the magnet structure?  The small black plastic piece looks like a pole piece on top of a magnet.

I've managed to remove the resonator from the top of the element as well as the coil diaphragm from the faceplate assembly and finally the faceplate assembly from the magnet structure.  

When trying to reassemble the faceplate to the magnet structure it's hard for me to align both without the faceplate pulling towards and making contact with the magnet structure (pinching the gap).  If the coil is still in place while attempting to do this I would expect to cause physical damage as the gap is only so wide and you need a strong pair of hands to keep the two parts from squishing the coil.  

Good news the element structure feels very robust and it may be possible to build a new coil diaphragm assembly and rework similar to how one would re-cone a speaker.  The diaphragm looks to be made of mylar with a coat of some type of substance, similar to what they dampen coated drum heads with only much thinner.

The humbucking coil measures 1-Ohm, the voice coil looks to be ~160ishOhms but I haven't verified.

I need to count the flutes on the diaphragm take weight of coil diaphragm and try to reverse the turn count on the voice coil.  The magnet wire looks to be copper of a very light gauge I'm guessing 40 or lighter.

Should be doable to take gap measurements, fab a mandrel, and with proper material/assembly to reconstruct a coil to adhere to an intact diaphragm.  Reassemble the elements and start taking measurements.

One issue I do see is there looks to be some damping cloth under the faceplate between the magnet structure (damping chamber) and faceplate.  Could cause issues if those values have changed with tinkering.  Debris, moisture, etc can over dampen and throw air resistance values all out of wack.

Also I'm not sure if the diaphragm is adhered to the faceplate, there appears to be a pink substance around the outer edge of the diaphragm as well as a washer of sort, but this diaphragm came right off with little effort....The diaphragm does stay nice and centered when just dry fitting, so it may be that the resonator keeps it in place.  I may at some point after winding up some coils try to adhere the diaphragm and then adjust the resonator to taste and see how that affects the high end.

fun fun,

 

[Henrizzle]

..another view of the broken pcb, you can see the tantalum that fell apart.

Hey MicDaddy,

I have a dead MD441U, I took it apart with the help of this thread, very nice thanks. So my board inside the can is not broken. I used a logic probe and the red wire from the capsule is connected to the red cable end at the hi-pass switch. The blue is connected from the capsule to the PCB but not through to the hi-pass switch. Is this normal or is the blue connection broken in the PCB?

 

[panman]

The blue wire measures open through the PCB, because there are capacitors between. Did you measure the capsule from the terminations (before going to the PCB)? Did you get c. 200ohms? If not, the voice-coil wire(s) is/are shot. Since you have it open, you can now also measure from the PCB. That`s the first thing to do and and the next is to check if the bass roll-off/XLR- connections are there. You were lucky if the PCB did nor break, when you opened it. It usually does, if you don`t know to do it right. And normally it is glued too to make it more difficult.
Let us know!

 

[David König]

I'll take pictues when I open the element again.

It is kind of weird: when you take it apart the way I described, you look at the diaphragm and coil *from below*. The other part is a kind of dome that fits below the center dome of the diaphragm and is very magnetic, of course.

If you still have faulty 441 (or generally ANY old vintage mic) you may sell it to me for reasonable price and I will fix it myself. Problem solved!