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Author Topic: KM84 damage worth repairing?  (Read 7848 times)

bricklayer

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KM84 damage worth repairing?
« on: March 21, 2015, 10:30:24 pm »

Hello, everyone. I received a KM84 from eBay that sounds pretty good, but as the pictures below show, when unscrewing the capsule, the capsule comes apart. Before returning the mic to the seller, I noticed another KM84 with the same issue selling at full price, so I contacted a microphone repair shop to confirm that the microphone I received is indeed damaged. They confirmed that it is but that it is a quick fix that the mic tech could talk me through. Apparently, the mic tech is swamped and hasn't gotten back to me, but based on this response I kept the mic rather than returning it.

What I'm wondering now is if it is worth sending in for repair and a full servicing, trying to repair it myself, or just accepting the microphone as is. Accepting it as is is hard to accept, because I'll never know if it could sound better. When I unscrewed the capsule I noticed a lot of dust on the curved white plastic portion in the body, so I assume that this mic hasn't been serviced in a very long time, perhaps never. How much better could it sound if I send it in for a cleaning and repair? I just don't know the answer, because I don't have another KM84 with which to compare it. Also, how much could full servicing with a repair like this cost me? Finally, I'd like to record with the mic fairly soon, so what are typical turnaround times for a service like this?

Thanks.
Jeff
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David Satz

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Re: KM84 damage worth repairing?
« Reply #1 on: March 21, 2015, 10:50:40 pm »

I bought a KM 84 on eBay about ten years ago with capsule in the same condition as this. Neumann USA told me that the capsule is a considered total loss if the pin has been removed; they don't consider it possible to reassemble the capsule properly without the tools, alignment jigs and post-assembly testing that are used at the factory when building new capsules.

Replacement capsules (or in this case "capsule heads") from Neumann USA cost about $600 each at that time as I recall; I haven't gotten a price quote recently.

When I complained to the seller, he refused to give me a refund. When I then complained to eBay, they were no help at all. They evidently have no clue what a capsule is, or how a microphone works. I ended up losing all the money. I hope this doesn't happen to you.

--best regards
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bricklayer

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Re: KM84 damage worth repairing?
« Reply #2 on: March 21, 2015, 10:59:40 pm »

That is terribly disappointing to read, but thank you for the response. I made what I thought was a good deal with the seller based on the mic tech's assurance that it could be repaired. But if Neumann doesn't think this is repairable? Oh boy.
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klaus

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Re: KM84 damage worth repairing?
« Reply #3 on: March 21, 2015, 11:36:24 pm »

As long as you don't mess with the backplate tensioning ring (the thin brass-colored ring in the first picture with the two indentations opposite each other, which determines the capsule's capacitance) you may be able to reinsert the contact needle, once you have reassembled the resonator and hand-tightened the needle. There would be no structural damage to the capsule, and it would continue to perform at the designated capacitance.

But you will need to find the second alignment pin! (One pin is showing at 5 o'clock of the resonator on the second picture.) The two pins properly align the backplate and resonator so that the cardioid of the capsule functions as intended.

It's really becoming a question of money and nebulous advice, and on both accounts you are a bit vague:

No one should have advised you that the damage is as quick fix over the phone (alignment pins are not available as spare parts from Neumann, though there are work-arounds). And you did not mention what"deal" was offered in consideration of the damage.

Put another way: If someone offered me a KM84 in this condition for $300.- I'd take it, and fix it, and donate it to our local Creative Music Guild. if the thing sets you back within reach of market price (anywhere from $900 and up) I'd pass.
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Klaus Heyne
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bricklayer

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Re: KM84 damage worth repairing?
« Reply #4 on: March 22, 2015, 12:49:04 am »

Thank you, Klaus. I don't mind sharing what I paid for it. I had assumed that it was perhaps tacky to do so on the forum. But after a long hassle, I agreed to pay $500 for it with the understanding that it would likely need to be sent in for that "quick" repair along with a standard cleaning/servicing to bring it up to snuff. That you now advise me that I should never have been told that I could be walked through the repair myself makes me wonder what I've committed to. I don't feel comfortable reopening the case with the overseas seller, so I'm left scrambling.

I was wondering about that alignment pin. It appears to be a tiny plastic dowel. Interestingly, exactly like mine, the second alignment pin was missing in that other eBay seller's current ad that I mentioned.
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bricklayer

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Re: KM84 damage worth repairing?
« Reply #5 on: March 22, 2015, 01:40:33 am »

Does the contact needle need to be reinserted in order for the microphone to work properly? What are the chances that, in its current condition, I'm hearing what a KM84 should sound like?
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klaus

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Re: KM84 damage worth repairing?
« Reply #6 on: March 22, 2015, 02:32:10 am »

The contact needle served two functions, both of which are disabled without it:

1. It makes the electrical contact between capsule (backplate) and mic amp (FET Gate), and

2. It affixes the resonator to the backplate

There is zero chance that you get any output out of the mic, let alone cardioid performance, without the contact needle. Therefore you cannot hear what this KM84 would sound like in the condition the capsule is currently in.

However, you could test the mic amp of this KM84 with a different capsule, if you had one available.
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Klaus Heyne
German Masterworks®
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bricklayer

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Re: KM84 damage worth repairing?
« Reply #7 on: March 22, 2015, 07:03:44 pm »

So I assume the contact needle is making some electrical contact even in its current state of disrepair? I recorded a little bit of my cedar top guitar through it, and I've attached a link to download the short 44k/16bit .wav file. The mic self noise is low, and the sound is focused, but I suppose I'm hearing an exaggerated nasal/honky/metallic sound which may or may not be characteristic of a KM84. Should it sound like this? The mic is running through a BG-1 mic preamp and Motu 828mkii interface and the file is uneffected except that I brought down the level of a couple peaks so as not to break listeners' eardrums.

https://www.dropbox.com/s/gi1jeizaeo1rrjd/KM84damaged%20test.wav?dl=0
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klaus

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Re: KM84 damage worth repairing?
« Reply #8 on: March 22, 2015, 10:10:43 pm »

This is all a Mickey Mouse operation and I am not particularly comfortable giving you advice which ultimately may not serve to restore the capsule to factory specs.

But here it goes:

You need to extract the resonator + needle from the mic body by pulling both straight out (don't lose the 6µ aluminum spacer at the center of the resonator, it's crucially important for the cardioid pattern!) If you just screw in the remaining capsule parts, as you seem to have done for your recording, you have no control over the contact needle's seat or torque, if any, to affix the resonator to the backplate. Therefore you have no control over the acoustic property of the whole capsule assembly, which likely will be off.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

bricklayer

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Re: KM84 damage worth repairing?
« Reply #9 on: March 22, 2015, 11:23:36 pm »

Thank you, Klaus. I certainly don't want to Mickey Mouse it. One last thing. Are you confident that someone experienced at microphone repair such as yourself could restore it to factory specs? I'm curious why you would choose to donate it after repair had you received one in this condition. Thanks.
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klaus

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Re: KM84 damage worth repairing?
« Reply #10 on: March 23, 2015, 12:28:44 am »

My hypothetical included a $300 max. price point- a nice gift for needy non-profits.

Please contact me privately if you need further advice or help.

Thanks
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

bricklayer

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Re: KM84 damage worth repairing?
« Reply #11 on: March 23, 2015, 05:49:07 am »

Okay, thanks. Just sent you an email.
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bricklayer

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Re: KM84 damage worth repairing?
« Reply #12 on: April 03, 2015, 01:31:42 pm »

I just wanted to mention to everyone that I ....sorry, rest of sentence deleted by moderator. No promotion (including promotion of moderator) allowed on this forum. See forum ground rules.

Thanks for understanding. KH
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David Satz

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Re: KM84 damage worth repairing?
« Reply #13 on: April 03, 2015, 08:53:27 pm »

But reading between the lines, is the microphone working OK now?
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bricklayer

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Re: KM84 damage worth repairing?
« Reply #14 on: April 04, 2015, 01:41:32 am »

But reading between the lines, is the microphone working OK now?

Yes. It sounds like a completely different microphone than before it was serviced. Very nice.
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soapfoot

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Re: KM84 damage worth repairing?
« Reply #15 on: April 04, 2015, 10:01:17 am »

glad to see a happy ending. I love a good KM84.
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