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Author Topic: AKG 414COMB - CK12 Oxidation?  (Read 2468 times)

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
German Masterworks
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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
German Masterworks
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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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