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Author Topic: Assembling an U87 "the right way"  (Read 3029 times)

Phantombox

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Assembling an U87 "the right way"
« on: December 21, 2009, 07:57:21 AM »

Hello Klaus.

A friend of mine has got several U87i's. One of them after disassembling presents the following problem: sound comes and goes as you move the XLR cable on the output of the mic, and I'm not even sure that its at the XLR connector itself. Also as far as I remember, the output should be much higher then it is right now. I think this is a typical problem on these mics if they are not reassembled correctly, but I just couldn't figure it out yet.
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compasspnt

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Re: Assembling an U87 "the right way"
« Reply #1 on: December 21, 2009, 09:07:58 AM »

What do you mean by "disassemble"?

How much was actually taken apart?
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Phantombox

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Re: Assembling an U87 "the right way"
« Reply #2 on: December 21, 2009, 12:37:19 PM »

The capsule was removed (not the capsules receiver) and the bottom part with the XLR male connector was removed by unscrewing the 4 tiny little screw (2 on each side of the frame). The bottom part was just removed to take a look at the wiring, no soldering in there was touched.
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Michael Brebes

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Re: Assembling an U87 "the right way"
« Reply #3 on: December 21, 2009, 02:40:27 PM »

Sounds like the switch in the XLR connector is going bad.  You can try cleaning it or just bypassing it.
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Klaus Heyne

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Re: Assembling an U87 "the right way"
« Reply #4 on: December 21, 2009, 04:26:25 PM »

Two more suggestions:

1. The battery/power switch is actuated by a stalk visible in the center of the XLR. When the bottom barrel is not carefully reassembled against the circular circuit board, the stalk can be misaligned, so that power will get to the mic only intermittently.

Carefully examine the mechanical function of the power switch for smooth operation when you press on the stalk's visible nipple in the center of the XLR.

2. At the other the end of the actuator stalk that penetrates into the XLR is mounted a primitive type of spring (a curved piece of brass) that is the actual connection to the electric on/off switch to the mic's power supply. The brass is bent easily with time, so that its force pressing against the momentary switch can sometimes decrease enough that it can no longer fully engage the switch.

Bend the curve of the spring to a slightly more open position. This will increase the pressure on the switch to trip it fully, once the actuator stalk is engaged by the XLR being plugged in.
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Phantombox

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Re: Assembling an U87 "the right way"
« Reply #5 on: December 21, 2009, 05:48:36 PM »

Just bypassed the switch. Problem is still present (sound comes and goes). Maybe its one of the 7 pin connectors at the capsule? When putting the shell over the mic and tightening the nut at the XLR connectors side, the capsule actually slides out a bit until nut and sleeve are completely tight.
By the way: are these pins really gold plated?
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Klaus Heyne

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Re: Assembling an U87 "the right way"
« Reply #6 on: December 21, 2009, 08:14:52 PM »

Yes, the pins are gold plated, and the head contacts never fail (at least until someone comes again and tells me he had 25 of them fail just last week.)


I am starting to think that you may have a capsule problem. Can you trigger the fade by breathing into the capsule, up close?
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Phantombox

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Re: Assembling an U87 "the right way"
« Reply #7 on: December 22, 2009, 12:51:28 PM »

OK. Now I switched the capsule with one of another U87. Problem is still there. After about ten seconds the sound goes away, then comes back, then leaves again and so on...
And , by the way: after these 10 secs it starts making a lot of noise that won't go away unless I disconnect the mic again and then the process starts all over.
Maybe its something with the capacitors? They are tantalum ones that usually don't need to be replaced. Or do they?

Also, a recording engineer told me some time ago that the shield of the XLR cable has to be connected to pin 1 to eliminate a kind of problem, I just don't remember which problem it was.
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Klaus Heyne

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Re: Assembling an U87 "the right way"
« Reply #8 on: December 22, 2009, 03:12:29 PM »

If the mic's shield were a problem, it would not fluctuate as you describe.

I would at this point engage a professional microphone technician (emphasis on 'professional'.) You just get confused with all these well-meant bits of advice, because you cannot filter their value, due to your lack of experience and their lack of access.

This is not unlike researching pain in your leg on the internet- without a road map, you get so deeply into it, you invariably end up thinking it's cancer...
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com
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