You are here

Half a U87...

Page 1 of 1

Half a U87...

PostPosted: Sun Sep 22, 2019 4:37 pm
by Ramirez
One of the old studio U87s (not Ai) has half-stopped working.

It seems that the front-facing diaphragm has died/disconnected. When set to omni mode, it seems to work like a cardioid (but obviously, the rear now being the sensitive side)

This happened while it was set-up and ready to go - I had checked the lines and the mic was fine. I then held it, and this happened.

I don't recall there being an obvious increase in noise between the normal cardioid mode and the new behaviour in omni mode. One thing I cannot remember is whether or not there was any signal present when set to cardioid. I shall check this when I'm back in tomorrow, as well as for any significant differnce in noise between the mic and the other (healthy) U87.

Does this point to a diaphragm failure (perhaps needing a rather expensive capsule replacement?!), or might it just have become disconnected / switch failure?

Aled

Re: Half a U87...

PostPosted: Sun Sep 22, 2019 5:41 pm
by Hugh Robjohns
Capsules don't normally just stop working unless the mic is dropped or seriously abused... but it is a possibility.

I'd like to think a more likely reason is corrosion of the capsule connector, or something else mechanical since you say it died when you handled the mic.

Which version of U87 do you have? The early ones (U87i and p) had electrically separate front and rear capsules, whereas the later Ai models have an electrically shared backplate, so the possible failure modes are different with the different models.

However, if the rear half of the capsule is still working, that suggests the biasing voltage supply is still working, as is the impedance converter electronics. So I'd check the capsule's plug-in socket first of all to see if that's become corroded or damaged in some way.

The other thing to check is that someone hasn't replaced the body backwards so that what you think is the rear is actually the front! :? It shouldn't be possible to do that with the switches and keyways... but never underestimate the obvious....

H

Re: Half a U87...

PostPosted: Sun Sep 22, 2019 7:10 pm
by Ramirez
Hugh Robjohns wrote:Capsules don't normally just stop working unless the mic is dropped or seriously abused... but it is a possibility.

I'd like to think a more likely reason is corrosion of the capsule connector, or something else mechanical since you say it died when you handled the mic.

Which version of U87 do you have? The early ones (U87i and p) had electrically separate front and rear capsules, whereas the later Ai models have an electrically shared backplate, so the possible failure modes are different with the different models.

However, if the rear half of the capsule is still working, that suggests the biasing voltage supply is still working, as is the impedance converter electronics. So I'd check the capsule's plug-in socket first of all to see if that's become corroded or damaged in some way.

The other thing to check is that someone hasn't replaced the body backwards so that what you think is the rear is actually the front! :? It shouldn't be possible to do that with the switches and keyways... but never underestimate the obvious....

H


Thanks Hugh

Its the older 'i' version I think, with the battery compartment. The two we have are quite old - it says 'Made in West Germany' anway, so I think it's at the latest an 80s model- perhaps around 1980, which is when the studio was built. I have a recollection that they were serviced a few years ago though.

I don't think the body is backwards, as the only person who would have done that is me... and it was working fine before! And as you say, I don't think the switches would allow it anyway. In any case, the 'front' is dead in omni.

Might it be wise for me to post a pic of the inside when I'm in the studio tomorrow?

Re: Half a U87...

PostPosted: Sun Sep 22, 2019 7:30 pm
by Hugh Robjohns
If it has the battery compartment it is a first generation model with the split capsule and 47V biasing (as opposed to the combined capsule and 60V boasting in the Ai model.

If you feel confident with a screwdriver it might be worth checking the capsule base connector, but if it's nothing obvious you'll need a good mic doctor...

Re: Half a U87...

PostPosted: Mon Sep 23, 2019 1:11 pm
by Ramirez
Thanks again Hugh


I'm comparing the faulty one side by side with the healthy one now.

Here's the behaviour:

Cardioid - No usable signal at all, BUT the DAW meters are responding very slightly to sound, so the mic is reacting in some way or another.

Omni - Front side dead, rear side OK. Proximity effect same as usual in omni mode (ie reduced compared to cardioid). Quite noisy (much noisier than the healthy one in omni), but constant, fairly benign pinkish noise.

Fig8 - Front side dead, rear side OK (polarity reversed as expected). VERY noisy, low frequency rumbling that's constantly changing, and some 'zipping' noise (perhaps suggesting a dirty capsule?)

I'll open them up to see if I can spot anything now.

Re: Half a U87...

PostPosted: Mon Sep 23, 2019 1:37 pm
by Ramirez
Nothing is obvious from a peek inside, but I'm not really sure what I'm looking for either. The soldering looks neater/shinier on the healthy one though...

Intriguingly, they don't seem to be wired exactly the same, and they have different capacitors despite the serial numbers being only 3 apart.

Speaking of the serial numbers, I think they are a bit older than I thought - I've emailed Neumann asking if they can date them, but going by other internet posts they are very early 70s if not even late 60s. I think perhaps the faulty one deserves a thorough inspection by Neumann themselves.

Re: Half a U87...

PostPosted: Mon Sep 23, 2019 1:43 pm
by Wonks
One may well have had its caps changed during a service.

Re: Half a U87...

PostPosted: Mon Sep 23, 2019 2:25 pm
by Ramirez
Wonks wrote:One may well have had its caps changed during a service.

That's the most likely explanation.

Further update - its now working... kind of.

I noticed the XLR connector was loose so I tightened that, and the front diaphragm periodically came to life. It seem that breath moisture cuts it off, and takes a few seconds to come back alive. I think this suggests a dirty capsule.
I had something very similar happen to my AT4050. They were reluctant to attemt to clean the capsule, and instead said that the capsule needed replacing (which cost almost as much as a new AT4050). I kept it as is, and I just don't use it on vocals any more.

A replacement U87 capsule is around £800 I think... and even then, would a new Ai capsule possibly devalue an old U87i? Capsule cleaning is the best option if Neumann would be willing - I shall contact them about that.

In the meantime I've chinagraphed 'No Vocals!' on it and ut it back in the drawer.

Re: Half a U87...

PostPosted: Mon Sep 23, 2019 2:29 pm
by Hugh Robjohns
Yes, it sounds like the failed one has been 'serviced' at some point in its life... I think a microphone doctor is called for.

H