Microfone failure

[FLUKE]

Hey,

I'm new here and I'm trying to find my way....
I got a question tough:
Recently I noticed something strange was going on with a few mics (Sony c48, U67) in our studio. They seem to be working fine but when the volume you produce goes up, the mic collapses. It's like a compressor working the wrong way.
Does anyone know what might be the problem???
Thanks,

F.

[DrDeltaM]

Welcome, always nice to see other Belgians

Maybe the Geekslutz know, moved this thread to the techy guys forum

[FLUKE]

Thanks!
Didn't really know where to put the post...
Cheers.

[gyraf]

Try not to breathe on the mics when you test them - condenser capsules don't like that at all.

Use a good pop filter, or test with something else than your voice.

Jakob E.

[FLUKE]

That's not the problem. No sound comes out of them anymore after that , unless I cut the 48v or the powersupply. When I put it on again, they work again until a certain level of soundpresure. I
I'm not really technical at all, but it seems like a capacitor unloads and doesn't reload... I don't know. All mics got the same problem at one point. Before they worked ok.
Thanks.

[rodabod]

It sounds like the diaphragm is maybe collapsing onto the backplate....

[FLUKE]

Any idea how this is possible?
Some people ask me if there has been alot of humidity in the studio but I don't think there was.
What worries me is that all the mics got the same problem. Could there been a peakcurrence while they were connected?
Cheers.

[gyraf]

Double-check the phantom supply?

[rodabod]

Try putting them in a dry airing-cupboard over night, or put them in sealed bags with Silica gel sachets to dry them out.

As Gyraf says, check your phantom power.

It could also be that all of your mics have very dirty diaphragms.

[FLUKE]

Thanks.
Phantom power is okay.
They've been in a closed (dry) closet for a few weeks now but no result....
I'll try the silica gel.
I'll keep you guys informed when I get any sollution.
Cheers.

F.

[lento]

I'm having the same problem also with Sony C48's.

I've just bought a couple secondhand and immediately noticed a drop in volume after the first word !
Also there is a background whoosh ( like the sea ) that is present.

I have a good working one to compare with so I know how they should sound.

Lyn

[lento]

After posting on the Sound on Sound forum, I received these useful comments.
Hope they may also be of use to you.


""They could well be old enough to have a capacitor problem - either in the internal circuitry or possibly the capsule itself. Your description sounds to me like a capacitor that's breaking down and failing to hold charge. I've had this with very old C451s (an internal capacitor breaking down), and a Neumann U77, a couple of AKG C12s and a C24 (capsules dying). They all went "wooshy" and their outputs fell away a few seconds after stabilising on power up. switching them off and giving them a minuite or two to settle before powering up again causes them to do the same thing. I've also had it happen with valve mics when the valve is giving up but they normally go noisy/thin for quite a while before the output vanishes completely.

Equally, as Wonky says, condensation/moisture and/or dirt on the capsule can produce similar effects if they lead to the capsule failing to hold charge. If the output isn't dying completely I'd suspect that the fault isn't completely shorting/discharging the capsule but causing the charge to leak away to an unworkably low level. Age/dirt/tarnishing or corrosive loss of the diaphragm plating rather than any specific mistreatment would be my guess (rather than moisture).

Another thought would be a faulty transistor in the internal circuitry. I've had this probem with some older European condensor mics where certain types of transistors develop hairline fractures which, in humid conditions, allow tiny amounts of moisture into the component causing it to drift out of tolerance becoming noisy or failing completely. These transistors often get worse as they warm up. Japanese mics seem to suffer this a lot less (I've never seen one with this problem).

I still think it's capacitor related though. Try Wonky's suggestion of letting them warm up and acclimatise for a while and if that doesn't work, refer them to a good tech (or back to Sony) for an overhaul. One slight problem might be, I don't know, but might be, that finding the parts could be rather difficult - worth trying though as they're nice mics. ""

Lyn

[Fleaman]

I have a similar problem with my AT4047.

I used it outside of a kick drum (about 6" from the hole) with triple (3!) pop filters and got a killer tone....for about 3 takes, then it loses about 20db and the tone goes to blah for the remainder of the day.

The next day I checked the mic and it seemed fine. Tried again on the kick, again it has a killer tone, then in about 2-3 takes, blah...out of gas for the rest of the day.

I was using the mics pad and the specs say the mic can handle 150db...but that is at 1khz.

I'm thinking the diaphragm was bottoming out on the backplate. 150db handling at 1khz seems like a lot, but I'm sure 100db at 50hz is moving the diaphragm more.

It still doesn't explain why the mic stayed 20db down for hrs later (after I took it off the kick drum).

Anyone have large diaphragm condensers poop out like this on a kick drum?

Anyone?

[FLUKE]

Wow,

Lento, it's definatly the same problem, I hear the sea too....
Moisture; could be, but ours have been in the closet for a month and still got the same problem.
Age/dirt; don't think so. All the mics got the same problem at the same time.
Capacitors; my guess too. We'll propably sent them to a good tech.

To be continued.......