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Author Topic: AKG C-414 B-ULS - Noisy  (Read 6333 times)

GYMusic

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AKG C-414 B-ULS - Noisy
« on: February 06, 2013, 06:53:08 pm »

AKG C-414 B-ULS, gold grill.  It has a random popping noise which seems to settle down a bit after being powered up for a half hour or so. 

If I enable the low frequency roll-off filter, the popping is greatly reduced, but still there.  This tells me the problem is most likely upstream from the filter.  The noise is worse in the cardioid position, which makes me think it's a problem with the front capsule.  Would you agree?

THX, GY

radiovinhet

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Re: AKG C-414 B-ULS - Noisey
« Reply #1 on: February 11, 2013, 11:18:14 am »

Gold grill - it's a C414 Tl-II!

The problem can be the capsule. If the noise get more louder in cardioid mode, the front membrane is possible dirty, and will be more sensitive to moisture, that will make some noise.
You can: swap the capsule sides (front to back)... or try to clean the diafragm.
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klaus

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Re: AKG C-414 B-ULS - Noisy
« Reply #2 on: February 11, 2013, 12:01:23 pm »

An easy and quite reliable method to determine whether a noise problem in a condenser mic originates at the capsule or at the mic's electronics is this:

If you can trigger, exacerbate, or otherwise influence the noise by accessing the capsule with your mouth up close through breathing or popping or yelling into it, it is a capsule charge issue. Most often a diaphragm contamination and or moisture issue.

If the characteristics and volume of the noise is unaffected by your adding SPLs, no matter how loudly you speak or yell or how moist you breathe into the capsule, the cause is electronic, and not the capsule.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Jim Williams

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Re: AKG C-414 B-ULS - Noisy
« Reply #3 on: February 16, 2013, 12:24:33 pm »

Clean the pattern selector switch. This is a common problem with those mics.
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GYMusic

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Re: AKG C-414 B-ULS - Noisy
« Reply #4 on: February 16, 2013, 08:26:53 pm »

I appreciate the replies.  Yes, it is a Tl-II.  Yelling/breath up close did not make the noise any worse.  I have a link to a WAV file of the noise.  The recording level is set at a vocal recording level.  You might have to boost to the level.  I thought it would be more useful to post it at a typical level.  I will clean the switches, but I have rocked them quite a few times and that doesn't seem to help.  I'm suspecting a noisy cap or XTR.

There's a pretty nice "pop" @ 22 seconds into the clip.

http://www.gymusic.com/audio/AKG414_Noise.wav

klaus

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Re: AKG C-414 B-ULS - Noisy
« Reply #5 on: February 16, 2013, 09:07:06 pm »

That points to an electronic culprit.  Troubleshooting an 8 transistor mic (corrected by Jim Williams: it's actually 16, counting power supply and amp sections! K.H.), and many capacitors (which this discharge sound may point to can be a pain.

Speaking from experience, the tantalum filter caps are notorious for phantom spike damage/overvoltage intolerance. I would start substituting these before anything else.
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Klaus Heyne
German Masterworks®
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GYMusic

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Re: AKG C-414 B-ULS - Noisy
« Reply #6 on: February 17, 2013, 11:44:24 am »

Yes, I'll give it a go and start with the caps.  TNX

Jim Williams

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Re: AKG C-414 B-ULS - Noisy
« Reply #7 on: February 18, 2013, 12:02:12 pm »

There are 17 transistors in that circuit and a number of capacitors. The pcb's are very tiny and the tantalum caps small and very closely packed. They are mounted right up against the connectors so usually you need to remove those before the caps, in other words, these are a tiny PITA to de-solder successfully. You will need very narrow width desoldering tools to avoid damage to ajacent components and quite a bit of skill.

Rather than 'shotgun' out parts nilly-willy, use a scope and trace the signal and find exactly where this problem occurs. Otherwise there is a very good chance you will damage this mic with un-neccessary parts swaps.

If the head amp is the problem, usually it's not a transistor but one of the four 3 gig resistors that are soaked in conformal coating. Removing them usually means destroying them so better you have a set of spares, IF you find this is the section exhibiting the problems. The yellow WIMA polycarbonate capacitors used in the head amp are no longer manufactured and are not available. You will have to re-use those parts if they are not damaged or fit in some inferior MKS mylar caps. When I used to rebuild these I would fit in 470 pf WIMA FKP-2's at 1000 volt ratings, much better than the stock polycarbonate caps, but a tough fit.

You can also send it to Richard Land in Nashville if you have any doubts about your abilities and the availability of spare parts. He will swap the card.
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GYMusic

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Re: AKG C-414 B-ULS - Noisy
« Reply #8 on: February 18, 2013, 06:38:54 pm »

I had an RF transmitter apart the other day doing some mods on an SMI board.  My hands are still pretty steady!  I've got a nice soldering pencil with some tiny tips and a magnifying lamp.  Years of experience, but age is making me question my confidence these days.  I'm thinking... I use canned freeze spray on audio amps to find the bad component in cramped spaces.  I usually use it in this same circumstance where the component is displaying intermittent noise.  Freezing it makes it act up.   

GYMusic

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Re: AKG C-414 B-ULS - Noisy
« Reply #9 on: November 18, 2016, 09:01:56 pm »

It's been a while, but I thought I would post my find.  I replaced the 330 uF @ 50 v electrolytics that were the problem.  Easy fix.

klaus

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Re: AKG C-414 B-ULS - Noisy
« Reply #10 on: November 19, 2016, 12:22:25 pm »

Thanks for following up! That really improves the quality of the thread and, by extension, that of the forum.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com
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