Neumann M49 trouble

Hiya,

I've got a problem with one of my M49's.
It has stopped producing sound.. in the recent past it did give some "elctrolytic-rumble" but now it has stopped working at all.
what i got so far:
- PSU is good (measures ok)
- output trannie measures 5 ohms on secondary side and 1k on the primary side
- swapped big 1uF cap, wasn't it.
- cable works, measures ok
- it's not the tube (i've swapped it for my spare AC701)

Could anybody help me with the next step...
I'm not that well on tube circuits, so if anybody could point me at the right direction i would be one happy chappy...

Thanks in advance!

Remco

have you tried Klaus Heyne's mic section in the Pro Sound Web forums? Oliver Archut over there knows his stuff about m49's.

not taking anything away from the guys here, but i dont know if thats a mic to be taken lightly.

sorry to be of no immediate help, i just wish i had a m49 and spare 701's to have the chance to break. :green:

goodluck.
t

Could be the capsule.

Did you check to see that all solder connections are good inside the mic? I had a dead KM-56 that turned out to be a resistor lead that had come loose.

Indeed. I had an M-49 do that. It made the "capsule is dirty" sound til it stopped. And it was the capsule being grounded by too much long-term spit between the capsule edge and the membrane.

Cleaning an old capsule can be a pain in the wallet. You need to think like an art restorer.

Is the capsule a M7 or a K47? The gold will lift from the PVC or PET if you let water sit to long on the surface. From the old capsules(>20years) I have cleaned it seems the PET has more of a problem with the gold falling off when the water gets behind it and lifts it away from the plastic.

What circuit is the amp fixed bias or Ver 3 cathode biased?

If cathode bias cheak the cathode cap with a good cap meter for leakage at about 5V the cap only has about 1.6V or so forming voltage this could maybe cause some problems if it is shorted.

I taught myself how to clean capsules with cheap china ones then Bad old real ones like a k67 gefell m7s.

The most important section is at the edge where the gold is not. Sometimes there can be a small bit of dirt or lint or fiber that bleeds the charge off. I use a optic brush with a very light touch to remove dust etc not "glued" with spit and smoke to the skin. This might be all you need.

Some capsules I don't even try to clean the middle area with water I just clean the edges because some gold will fall off no matter what you do and the added mass is still small compared to the mass of the enclosed air.

You could also have a capsule that is beyond repair.

A close up picture would help.

The problem with DIY cleaning is it is easy to destroy a capsule. Like I said I bought an old 67 that I tried different things untill I found the safest way to clean old capsules then I sent it to Doug Walker to get reskinned.

New capsules the gold sticks a lot better.

Seth did you ever strap the 56 to 200 ohms?

Gus - I could never identify the terminals on the transformer so I didn't mess with it. I looked around for a picture or something but I couldn't find anything that made it clear to me. I thought I had it at one point but it didn't work so I put it back and left it alone.

Hi guys,

thanks for the replies, i had 2 gigs so i was kinna late with a reply

The capsule has been replaced bij Neumann Germany 3 years ago, so i really hope it's not that. I've included a picture of it
www.beunhaas.biz/thelab/capsule.jpg

I will try tonight if it could be soldering or the grid-cap..

Thanks again!
Remco

back again..

And guess what.. i found it..
After measuring every component to check value i came to wiring.
What it turned out to be was a connection in the base of the mic on the connector came loose.
Right under the rubbersuspention..

And ofcourse that was the HT..

thanks for putting me in the right direction guys!

Greetz Remco