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Author Topic: AKG 414COMB - CK12 Oxidation?  (Read 5368 times)

mutterd

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AKG 414COMB - CK12 Oxidation?
« on: June 09, 2016, 12:47:30 am »

Hey everyone - could you please have a look at this and tell me what you think it it?

I just bought the mic, there was some damage in shipping and I'm trying to decide weather to ask for a partial refund or to send it back.

A friend said it was the gold scraped off from a bad cleaning, another friend said its the gold starting to flake off the mylar.

I tried it out on an acoustic cello and it sounded good, had lots of low end but wasn't as bright as I expected. I have used CK12 EB's and it seemed a little duller than id expected...

Next I tried it as a floor tom side drum mic in Glynn John and again - loads of lowed but maybe not the air...

anybody seen anything like this before?

I will post photos and can provide audio files if anyone is interested.

thanks so much guys,
Timothy

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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #1 on: June 09, 2016, 12:57:43 am »

Here are some shots of the other side of the capsule - has a little dab of something with some fibers stuck in it....
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klaus

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #2 on: June 09, 2016, 01:05:28 am »

Aside of a small area of reduced sputtering density, the front diaphragm surface looks fine. Such small amount of sputtering loss will not affect the performance of this capsule. I cannot comment on the "dabs" (most likely indentations) on the rear diaphragm, as your pictures are not close enough and too low in resolution.

The frequency imbalance of the mic in cardioid is unrelated to the sputtering loss, and may have the following causes:

1. Diaphragm tension loss

2. Wrong spacer thickness between diaphragm and backplate

3. A CK12 on one end of a very wide spectrum of "acceptable"  frequency performance

I would try to reverse this capsule, to determine what options you may have:

First, remove the red wire from the rear diaphragm, then listen to the mic in cardioid. Then remove the front wire (green) and mount it to where the rear diaphragm wire (red )was mounted. This will give you an objective comparison between to nominally identical cardioids. You will find that they most likely will sound different. If you like the sound of the rear side, have an expert mic tech reverse mount the capsule, and use that side from then on as front (cardioid) side. If the rear also sounds muffled in your listening test, return the mic to the seller.

Best of luck!
KH
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Klaus Heyne
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #3 on: June 09, 2016, 02:27:24 am »

Wow - thanks so much Klaus - I will try swapping capsule sides out tomorrow - thanks so much for that.

sorry for the photos - I will post some better ones.

the "dab" almost looks like a drop of water or spit or something - much bigger than the spray residue on Neumann's...

here is a higher res version of the side with the sputtering density issue.
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #4 on: June 09, 2016, 02:29:12 am »

and the other side with the "dab"

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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #5 on: June 09, 2016, 01:21:49 pm »

Klaus-

In testing the sides of the capsule - is it safe to loosen the screw and remove the lug?

Or is it better to resolder...

Thanks so much!
Timothy

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klaus

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #6 on: June 09, 2016, 02:28:54 pm »

Removing the screw is preferable to unsodering the wire from the eyelet: soldering would take place too close to the diaphragm, and hot rosin may splash onto the diaphragm plastic and burn holes in it.
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Klaus Heyne
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Kai

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #7 on: June 09, 2016, 06:59:31 pm »

...soldering would take place too close to the diaphragm, and hot rosin may splash onto the diaphragm plastic and burn holes in it.
The little drop you can see in the picture is very likely one of those.
I always build a little pocket from paper to protect the diaphragm when soldering.

Even then I absolutely avoid soldering the center tap on Neumann (luckily not in this case) style capsules.
The tap would need to be unscrewed and refited which is a delicate job.
Soldering this one in place would very likely overheat the diaphragm.
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #8 on: June 09, 2016, 11:15:50 pm »

yeah - the thought of a soldering iron in that proximity to the capsule was slightly panic attack inducing...

thanks guys - will let you know how it goes.

T.

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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #9 on: June 12, 2016, 11:49:29 am »

Ok - so heres a quick update.

I took the mic into the workshop last night with the intention of trying out the individual Cardioid sides as Klaus recommended.

I set it up to do some listening tests - was the first time i ever really set it up for any sort of vocal's aside from just talking thru it when i first got it. I did some tests above a drum kit comparing it to my '71 u87 and I used it for a session on a cello - both sounded ok, with good bass and low mids but slightly dull...

I was pretty immediately taken aback at the mics sensitivity to plosives - it pretty much thumps out in all patterns as close 30cm/1' away.

Is this normal?

I took the head basket off and noticed a slight bit of wrinkling around the edge by that weird "dab" but i wasn't able to really get a photo of it...

after that i inspected the leads to the solder tabs that attach to the capsule and there is no way i could get the green tab around to the other side - its a short lead to one pole of the mic pattern switch and I'm not sure if its been modified, but its no more than 30mm/1.25"...

so tell me guys - am I beating a dead horse here?

thanks so much for the help/advice.
Timothy

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klaus

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #10 on: June 12, 2016, 12:24:12 pm »

The low end collapse could indicate a fatal capsule condition.
Rather than have you pull on a wire to make it reach to the other side, make the blow test which will indicate whether your capsule suffers from low diaphragm tension:

Set the mic to figure eight. Blow a strong, steady stream of air from your mouth onto the front diaphragm, after setting up a bright light that reflects in the diaphragm. Now observe how soon the diaphragm returns to its resting position after being pressed against the backplate by the air pressure.

While you blow, you will observe the rough outline of the backplate through the thin skin of the diaphragm. That outline should disappear within less than a second after you stop blowing. If not, the capsule's diaphragm is shot and cannot be restored to factory spec performance.  Confirmation of very low diaphragm tension is when the stuck diaphragm section immediate spreads to the whole surface area within milliseconds.

Repeat the test on the rear side. If you have low tension on just one side, return the mic to the seller.
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Klaus Heyne
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #11 on: June 18, 2016, 02:47:59 pm »

Update #2.

Just set the mic up on a stand with a flash light in hand, mic switched to figure 8, and against better judgment, blew on the capsule.

I was fully expecting to see some action, but I saw nothing - moved the light all-around and kept going at it - all i saw was 1 tiny dimple on each side, like i was pushing the capsule down with a pin, and that was only when i was really blowing...

turned it around and same thing - no bottoming out... just 1 tiny dimple. no wrinkles on the edges, no outline of the backplane...

if i monitor it of course its goes nuts - but without sound i observed very little...

I confirmed again the popping "p's" and indeed, its thumps right out, but not visually...

good news? or bad news?

thanks so much Klaus.
T.

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klaus

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #12 on: June 18, 2016, 03:11:54 pm »

If your observation was correct, the diaphragms are fine. When applying air to the diaphragms, they should indeed bottom out for a split second, but recover fully immediately.
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Klaus Heyne
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #13 on: June 18, 2016, 05:55:48 pm »

So possibly an electronic overload? Is that something you see?

I have yet to open the shielded box...

Thanks so much.
T.
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klaus

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #14 on: June 18, 2016, 09:33:37 pm »

I am still unsure what exactly may be wrong with this mic.

You wrote earlier "it pretty much thumps out in all patterns as close as 30cm/1' away".
What does "thumping out" exactly mean? Did you ever compare it to any other C414 with CK12 capsules? Are you maybe not familiar with the rich low end these capsules produce, compared to similar Neumann products?

Bottom line: If you found something wrong with the mic, it may need further clarification as to the exact phenomenon you experience.

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Klaus Heyne
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Kai

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #15 on: June 19, 2016, 01:27:41 pm »

So possibly an electronic overload? ... I have yet to open the shielded box...
Once you measure the amp like a proposed you will know.  Before I wouldn't open or unsolder anything.
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klaus

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #16 on: June 19, 2016, 01:38:06 pm »

Kai,
In this thread, I cannot find your proposal to measure the electronics of this mic. Can you please (re) post it?
Thanks,
KH
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Klaus Heyne
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Kai

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #17 on: June 19, 2016, 05:06:31 pm »

...I cannot find your proposal to measure the electronics of this mic..
How to measure the electrical frequency response of a condenser mic's amplifier:
Feed in a sine wave generator's signal where the capsule is connected, via a ca. 1nF cap (exact value not critical, no elco, use a foil or ceramic)
Capsule can stay in place, no soldering necessary.
Level should be about 40mV.
Connect the mic to it's usual record path and use whatever meter is availabe, while tuning the generator frequency from 20Hz-20kHz.
If:
- the response is within a few dB from 40Hz to 15kHz,
- no audible distortion is present (most mic's can take up to 200-800mV without distortion, check specs),
- the output level is about what you get from a very loud voice from 20 cm distance from a known working microphone,
the amplifier is likely not broken.
Most condenser mic's amps have a gain of about 1, this means what goes in comes out.
So if you have the possibility to measure mV voltage you can check for that.
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mike zietsman

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #18 on: December 09, 2016, 06:02:38 pm »

My experience with brass capsule 414s is that they are generally quite sensitive to plosives.

I've only used about five of them (none of which had any obvious tension issues) but they were all very very sensitive to plosives and benefitted from pop filters at just about any distance. More so than any of the u87's I have.

Lovely microphones though. The capsules do something that you absolutely can't get out of the LDC Neumanns I have used.

Has anybody else had any different experiences with them in terms of popping?
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klaus

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #19 on: December 09, 2016, 06:24:42 pm »

Any LD capsule that is not center-supported would have a higher propensity for popping, all else being equal.
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Klaus Heyne
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #20 on: December 16, 2016, 11:35:18 pm »

Kai - thanks so much - this is amazing - I totally missed this response till just now but actually had the mic open again today - I have a full Audio Precision test set up so benching and determining THD and frequency response should be fairly straight forward.

my one question is this - when inputting the 40mV - should that be across the 1GΩ resister labeled R2 on the schematic, which is from the output of the capsule to common?

I will post results as soon as I've had a chance to run the tests.

and thanks again.
Timothy


How to measure the electrical frequency response of a condenser mic's amplifier:
Feed in a sine wave generator's signal where the capsule is connected, via a ca. 1nF cap (exact value not critical, no elco, use a foil or ceramic)
Capsule can stay in place, no soldering necessary.
Level should be about 40mV.
Connect the mic to it's usual record path and use whatever meter is availabe, while tuning the generator frequency from 20Hz-20kHz.
If:
- the response is within a few dB from 40Hz to 15kHz,
- no audible distortion is present (most mic's can take up to 200-800mV without distortion, check specs),
- the output level is about what you get from a very loud voice from 20 cm distance from a known working microphone,
the amplifier is likely not broken.
Most condenser mic's amps have a gain of about 1, this means what goes in comes out.
So if you have the possibility to measure mV voltage you can check for that.
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Kai

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #21 on: December 17, 2016, 01:35:47 am »

I don't have the schematic of this specific version, feed in where the signal wire of the capsule is connected.
You don't break anything if you try which wire is the right one.
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #22 on: December 17, 2016, 11:00:55 am »

HA! thanks - attached is the schematic.

as an aside (since I'm posting this) - I just got another C414 COMB and the previous owner has said that the tantalums need to be replaced - I see a 10uF across the 9V zener and the output is a 33uf - I was wondering if anyone you knew off hand what voltage values those should be. I was thinking 16VDC across the zener - but the 33uf looks bigger - 35VDC? - it looks to be biased about 3/5's of the way down from B+.

thanks everyone.
T.


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Jim Williams

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #23 on: December 17, 2016, 11:48:39 am »

16 volts ought to be enough with the 9v zener clamp. The output will see around 1/2 the phantom voltage so use 35 volts. The BC413 is a bit noisy, a BC550 or Toshiba 2SC3329BL will lower that noise. Also check the 470 pf input cap, I've seen ceramics used there. It's best to swap that with a polystyrene film or in a pinch a WIMA 470 pf FKP-2 polyprop cap.
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Kai

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #24 on: December 17, 2016, 12:46:53 pm »

...16VDC across the zener - but the 33uf looks bigger - 35VDC? - it looks to be biased about 3/5's of the way down from B+
If the values in the schematic are correct B+ is about 10V, clamped down by R3-Zener-R2. Remember the phantom power combined source resistance is as high as 3.4 kOhms (2x6.8k ll).
So no larger value then e.g. 16V is needed.

 For the measurement, feed in across Rz (1 G Ohm).
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mutterd

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Re: AKG 414COMB - CK12 Oxidation?
« Reply #25 on: December 17, 2016, 01:38:21 pm »

Thanks Jim - and yes it does indeed have a Ceramic disc there which i thought a bit weird directly in the signal path...

im pretty sure I have some BC550's kicking around - maybe i'll try that as well.

Kai - thanks for that - I'll give it a shot tomorrow and let you know how it turns out.

Thanks guys!
T.


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