buschfsu

faulty m7
« on: April 14, 2008, 11:21:05 PM »
Hello all
I have a microtek geffel m692 with 2 capsules.  I sent the 692 for the 12 to 48 mod  and the small diaphram and they checked out ok.  Th m71 large diaphram with the m7 capsule  has a really low output and distorts with a lot of gain.  Anyone know how these capsules go bad or if they are repairable
PRR said...
OHM'S LAW. Not as an abstract thing: you should be able to glance at a small circuit and "instantly" know I and V, the way a soccer player glances at the ball and knows the angle and kick


pucho812

faulty m7
« Reply #1 on: April 15, 2008, 12:06:16 AM »
There is not much to a capsule so from what has been said around here, capsules can go bad and are repairable.
usual symptoms
1.dirty
2.take on moisture sometimes causing the membrane to lift or wrinkle
3.starting to loose the gold sputter


I am sure they are some more but can't seem to think of any

there is a good lessons on how to proper clean a capsule. thanks senor SSL tech.

as for moisture use a silica pack on the capsule and it will eventually dry out. Although I am suspect on how long it takes. I had a capsule with condensation on it and it took longer then was suggested for it to dry out.



last one is left for the experts....

edit the M71 is cardioid only correct? If so and the capsule is sputtered on both sides you can use the back and see if that helps out. It's a nice way to test the capsule as well.

Look up my thread on the 147 mic that I recently serviced. lot of good info  in it.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

rodabod

faulty m7
« Reply #2 on: April 15, 2008, 05:08:27 AM »
What polarisation voltage is your MV692 set to provide?

It's a consideration when using the M71 as far as I remember.
Quote from: tv
punchy fat bastard chip

Sredna

faulty m7
« Reply #3 on: April 15, 2008, 06:13:59 AM »
If the MV692 wasn't tampered with, the polarisation voltage should be ok for a M71. If the voltage would be higher, it'll likely be the smaller capsule to have problem with that.

Try to watch the membranes through the mesh with a bright light.
They sometimes collapse and you could see it as a quite large wrinkle.

Mikrotech Gefell does repair that. It's not cheap but well worth it.
Hmm... in which direction do the electrons actually go?

faulty m7
« Reply #4 on: April 15, 2008, 09:50:16 AM »
If its an old M7 capsule, the glued edge sometimes separates in small
sections along edge where the membrane meets the outer ring of M7
causing your problem and giving it a cleaning will make it worse in most cases.
Does it have the notorious cracking in the membrane ? PVC or Mylar ......

Send it to Gefell in Germany there currently making the best M7 available,
but they charge up to 600 euro for services per capsule.
at Gefell contact : M.Militzer(at)microtechgefell(dot)de

Theirsch will re-skin capsules
repair/ reskining of sound transformer Mylar red line:       90EUR
repair/ reskining of sound transformer PVC blue line:     160EUR
 , but it may not sound exactly like a factory Gefell job.
Contact Theirsch : post(at)thiersch-mic(dot)de


Peluso Labs
http://www.pelusomicrophonelab.com/capsndiaph.html

I'm wondering if Dale Ulan (forum member) could be a repair source now or in the future ?
curiousaudioparts at  gmail  dot  com
https://sites.google.com/site/diypartsstore/

Gus

faulty m7
« Reply #5 on: April 15, 2008, 09:59:46 AM »
I don't know about the M71 but the um70 head has two plugs that you can remove and then unscrew two screws and take the head apart.  Maybe the capsule needs to be cleaned?

buschfsu

faulty m7
« Reply #6 on: April 15, 2008, 11:17:46 AM »
ill take some pics tonight and post.  its an older m71 with silver front screen and black back screen.

thanks
PRR said...
OHM'S LAW. Not as an abstract thing: you should be able to glance at a small circuit and "instantly" know I and V, the way a soccer player glances at the ball and knows the angle and kick

buschfsu

faulty m7
« Reply #7 on: April 16, 2008, 08:27:57 AM »
ok ill post the pics tomorrow, but the short of it is the capsule looked to be in good shape just a little dusty.( nothing like keiths barnancle encrusted hockey puck of a u87)  i did notice a little wavyness in the mylar at the top of the capsule and since there are no screws on the edge (only a black plastic ring) i applied sligt pressure by pinching the top and that seemed to strech the mylar back in place no more waviness and the capsule sounds great.  i wiped the capsule of with lens paper very gently.  thanks guys.
PRR said...
OHM'S LAW. Not as an abstract thing: you should be able to glance at a small circuit and "instantly" know I and V, the way a soccer player glances at the ball and knows the angle and kick

faulty m7
« Reply #8 on: April 16, 2008, 03:31:24 PM »
wavy membrane , which capsule are you referring to ? 71 or 692 ?

no screws , sounds like your talking about the M7 , yes ?

did it lift from the ring in a small section causing wavyness in membrane ?

hopefully your snapping pics of before and after image to show us ?
curiousaudioparts at  gmail  dot  com
https://sites.google.com/site/diypartsstore/

 

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