Sennheiser MD441 lost frequencies

[saint gillis]

Hi I'm trying to fix this microphone.
Here's the schematic :

  Here's my problem, sometimes it sounds like a huge high pass filter, very thin voice, no low end, like those old cheap telephones.
  And then 1 hour later, it sounds good again. And then another day, big high pass filter again. I try to find a logic, to move the components inside the circuit to see if it changes something, but I can find any logic routine...
  I was suspecting the 100n capacitor, in fact I've changed them all, but it didn't help.
  Any idea?

 

[saint gillis]

I must say, when we change the switch position during the issue, the problem persists, so it couldn't be this 100n cap anyway...

 

[Khron]

I assume you might've already come across this?

https://www.gearslutz.com/board/geekslutz-forum/607724-md441-repair-help.html

 

[saint gillis]

Yes, so groupdiy is now the place to be to get the schematic. And BTW the cap the guy is talking about is 0.33µ, not 33µ. But the thread didn't help for my specific problem...

 

[abbey road d enfer]

I assume you might've already come across this?

https://www.gearslutz.com/board/geekslutz-forum/607724-md441-repair-help.html

Ah! Gearslutz! I can't believe how this guy is pontificating about not using phantom power on a dynamic mic without an isolation xfmr.

 

[pucho812]

Ah! Gearslutz! I can't believe how this guy is pontificating about not using phantom power on a dynamic mic without an isolation xfmr.

from the first post of the slutz thread.

Saw an 'As-Is' non-working MD441 on ebay for too low of a price to stay away heh

Sure enough it showed up dead, no audio at the XLR, dc resistance between pins 2 and 3 showed open.

it sounds like he is surprised that it showed up dead, I guess non working as is means something else? ;D

 

[gyraf]

..actually, "no dc resistance" is a good sign, as it points towards xlr wires broken off, not capsule discontinuity (because lowcut electronicas also shows up as dc resistance path)..

On the other hand, loosing low-end intermittently could be a bad sign, if it comes from contamination of the magnetic gap or coil assembly getting stuck/loose..

 

[abbey road d enfer]

from the first post of the slutz thread.

What do you mean? You know a properly designed balanced dynamic mic can't be harmed by phantom...?

 

[saint gillis]

So it looks like the problem was that the roll-off switch was dirty and was making some unwanted capacitance between the tracks. I've cleaned it and it solved the issue.
But now there is another problem, the mic works fine with a soft voice, but is distorting  with loud signals like a snare drum for instance, is that a capsule problem?

 

[telewulf]

Hello Saint Gilles, hello everybody,

I know it´s been five years and maybe nobody cares anymore, but I dug deep into a 441 over the last days myself and made a drawing of the Hi-Filter. It is similar to your drawing but not quite the same. I´m pretty confident though, that mine is correct, especially concerning what is a transformer (Ü) and what is a tunable inductor (Dr). But although I´ve checked several times and couldn´t find any mistake, I have to confess, that don´t realls understand it

best wishes from Bremen,
Wulf

 

[Whoops]

Don't know if you guys ever saw this document,
but here you can find a very nice report on how to fix an MD441 microphone:

http://www.bymm.de/documents/11/Reparaturbericht_MD441_V0_3 English Translation V2_3.pdf

 

[Whoops]

and here the Service Manual, although there's no schematic there:

https://cdn.imagearchive.com/groupd...15a7ffff4663d3a64b0ac3a4e5c04530cd20c5c9a13eb