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Author Topic: Noisy AKG C 414 EB  (Read 619 times)

NickL

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Noisy AKG C 414 EB
« on: June 13, 2017, 05:57:16 pm »

I'm looking for a little guidance. I have a vintage AKG C414 EB with the brass capsule. There is clearly something wrong with it as lately. Its output is very low volume and the high end is mostly gone.

I want to know if this microphone can be repaired. I don't mind spending some money as I know it's a valuable mic and it used to sound great. I just don't want to spend a lot of money on it and then end up with a teflon capsule.

I would appreciate anyone telling me their thoughts on the meaning of these symptoms, and getting a consensus on whether or not this is a repairable issue. If the capsule was blown would it be making any sound at all? Is it possibly just dirty? Thanks in advance for any light you can shed on this for me.

Best, Nick.
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klaus

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Re: AKG C 414 EB
« Reply #1 on: June 13, 2017, 09:19:55 pm »

Hello Nick,

You don't provide a ton of information about the defect you discovered in your mic:
Can you influence or change the bad sound by speaking loudly or popping into the capsule, or by switching patterns? Does it sound equally dull in the back (figure eight or omni)?

There is a reasonable chance that your CK12 has lost diaphragm tension, at least on one side, if not both.
If that is so, there are no solutions but to buy a used CK12 on the market. This is especially true if you want to retain the value of a C414EB, which, equipped with the CK12 brass is worth about four or five times as much as one equipped with the Nylon/Teflon CK12.

So, next step, confirm my suspicion: take off the four slot screws at the bottom of the mic, strip off the metal housing, flip off the two basket halves, and observe, under good lighting conditions, whether one or both diaphragms are sucked in when you apply phantom power, or when you switch patterns from cardioid to figure eight.
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com

NickL

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Re: AKG C 414 EB
« Reply #2 on: June 14, 2017, 10:09:15 am »

Thank you, Klaus. I will try this and get back to you with the results.
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NickL

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Re: AKG C 414 EB
« Reply #3 on: June 14, 2017, 11:40:10 am »

Hello Klaus,
Well, I did as you said but I cannot see any evidence of either side being sucked in. There was no indication of that - unless it's REALLY subtle.

I changed patterns and turned the phantom power on and off but saw no effect. I did this under good light and both sides look flat and uniform. I will say, however, that the front looks very dirty. (The mic used to belong to a large, commercial studio and was used quite a lot.) However, when I reassembled the mic, the sound was vastly improved. The front of the mic sounds very good.

There is an exceptional amount of "handling" noise (I don't know if that's common for this model) and very loud sounds when I change the patterns. I tried omni and figure eight. They both appear to be working but the sound in the rear is certainly duller than in the front of the mic. Again, I don't have a clear sense of what is to be expected so the result is difficult to gauge.

I have read very high recommendations of your work. Is it possible for me to have you go through the mic and see what's going on, clean it, correct any loose connections etc.? Can you give me an idea of what a routine cleaning and maintenance would cost? If it is the diaphragm tension, then I can make decisions from there but at the very least, I think it needs to be cleaned and serviced. Are the conditions I described consistent with the loss of diaphragm tension? Do the symptoms of that type of failure occur intermittently? Thanks again for all of your help.
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klaus

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Re: AKG C 414 EB
« Reply #4 on: June 14, 2017, 02:11:06 pm »

Hello Nick,
First and foremost, I try as hard as I can to avoid what others are often tempted to do, and what I dislike with a passion: self promotion on an informational forum. Contact me privately for any work-related issues.

Regarding your questions:

"Handling" noise is common on C414EB. The handling noise is due to insufficient damping of the capsule against its frame, against the frame's hard rubber mount on the amp chassis. This kind of noise is in the 50-200 Hz range and hard to tame, given the tiny body of this large-diaphragm mic.

Pattern-and attenuator-switch rumbling and discharge noise, when actuating the switches ,can be tamed to a degree, on this model: AKG used primitive plating on the contact surfaces, which needs to be cleaned and re-lubricated periodically with an anti-oxidization fluid.

It is quite possible that the dirt and dust accumulation on your mic's diaphragms and backplates could be the cause of attenuated top end response: When the dirt load gets high enough, the 6 membrane can no longer follow fast (high frequency) wave lengths.
When a mic sits openly over long periods of time, airborne dust will continually fly to the unprotected capsule form as far as 6 ft. away, due to the electrostatic charge on the backplate (polarization voltage and its residue, even after disconnecting the mic from power). Capsule restoration to factory stock is often possible, provided there is no other diaphragm deterioration (see below).

If your capsule suffers from diaphragm tension loss, there is no remedy, as the diaphragms are glued to the diaphragm rings and cannot be re-tensioned.


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Klaus Heyne
German Masterworks
www.GermanMasterworks.com
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