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Author Topic: Original AKG CK12 Capsules: Sound, Lifespan and Repair  (Read 26539 times)

klaus

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #15 on: February 17, 2013, 02:34:26 PM »

Motorboating CAN be a sign of capsule deterioration- most often it's moisture discharges, due to diaphragm contamination.
Injuries to diaphragms can also cause momentary shorting to the backplate, with the same symptom of motor boating.

Unfortunately, electronic component deterioration sometimes also shows up through motorboating discharges.

Signs of capsule deterioration always include audible artifacts to the signal. So I would not be concerned if the sound of the mic is as it normally would be.

Here are some of the audible signs of capsule deterioration:

* excess distortion,
* gross frequency response aberration (on CK12 usually a severe drop-off in low frequencies, or, worse, telephone-like response 
   with pronounced mids and not much else), and, most often,
* discharge noises, like background thundering, slow farting sounds and other odd, irregular discharge sounds

In all of the above cases, the cause for the noise may also be an electric or electronic one, so additional steps of confirmation (f. ex. can the noise be triggered or altered through close breathing onto the capsule?) need to be done.
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Klaus Heyne
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mike zietsman

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #16 on: February 17, 2013, 07:15:32 PM »

As always, thanks for your help Klaus.

Strangely enough mine sounds fine (I think it sounds quite good and definitely emits a full frequency response that is free of obvious distortion) Breathing on the capsule gives maybe half a second of static, sending a short sharp plosive into the capsule gives a short sharp click (no doubt the sound of the capsule bottoming out?) but the mic recovers immediately in all patterns. (I don't do any of these tests often! Only after the motorboating became evident)

However tapping the side of the mic makes the motor boating become worse, as does tipping the mic on it's side.
(this happened in two locations and it is not just the mic picking up stray mechanical noises)
If i recall correctly it is worst in figure 8.

The only solution that I could find online to the motorboating was to change the tantalums. My tech changed the tantulum capacitors which made it much better (and made the mic usable again) but it is still slightly intermittent (whereas before it was constantly present and intermittently got worse).

I found one suggestion online (on another forum - to someone else with a similar problem) to replace the three diodes on the dc converter board but my electronics knowledge is insufficient to know if this is a good idea and my tech said that they were unlikely to go bad or cause motorboating. (aside from the fact that I am not a huge fan of just replacing parts in things "just incase" because of an anonymous message on the internet).


In the next couple of weeks a friend in a different part of the country is giving me a 414eb with a broken capsule and (as far as he knows) functioning electronics. changing the capsule into this mic should be a revealing process.

In the meantime I am going to use the mic in non-critical applications to discern if it is actually giving real world problems.

If anybody has anything that might point me in the right direction it would be greatly appreciated - I fear that I have a capsule arriving at the beggining of it's end (though reading Klaus's last post eases my fears a great deal).

failing that I will report back on anything that I find out.

Thanks,
Mike
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klaus

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #17 on: February 17, 2013, 08:18:13 PM »

I agree with your tech: the diodes are unlikely culprits.

But you seem to have something that is repeatable: positioning or mechanical pressure on one side of the mic.

Do this: remove the square housing and then plug the mic back in. With a fiddlestick (a non-conductive stalk) poke around the area that triggered the motorboating while the housing was still on. Despite the increased hum, due to the lack of shielding from the missing housing, you should be able to hear any changes in motorboating.

Likewise, if all motorboating has stopped with the housing off, maybe there was intermittent contact between an electronic component or wiring and the (conductive) housing? Probe around for possible tight spaces in the amp compartment, and possible contact/shorting between components and housing.
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Klaus Heyne
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GYMusic

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #18 on: February 18, 2013, 07:16:31 PM »

The three main issues that I have had with them are:

1: Almost universally I found myself having to apply quite heavy cuts in the 120 - 230hz region to compensate for a very obvious resonance there that would otherwise act to blur a lot of higher frequencies and make voices sound obviously muddy.

2: Sibilance (when present) was often 'smeary' and difficult to isolate as it would occur at several harmonics making harshness a problem - it almost seams counterintuitive but this harshness often made it difficult to bring 'airiness' and 'detail' into voices. You would almost expect a harsh mic to have detail but I often found myself thinking that vocals sounded harsh and lacking detail.

3: I found the midrange difficult to sculpt.

I have a 414 B-ULS and a Tl-II.  I have noticed the same issues when using as a vocal mics.  I recently tried recording with the filter engaged for 150 Hz.  That really helped with the bottom end sitting better in the mix with little other post EQ.  I also use a Shure KSM-44 for vocals and they seem to exhibit the same tendencies as you point out (around 200-500 Hz), but I like the top end a bit more with the 44.  I couldn't help but chime in when I read of the issues we shared.

GY 

usattler

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #19 on: February 19, 2013, 04:29:12 PM »

What ever happened to the simplest and reliable method to determine whether crackling is caused by the capsule or a component in the electronic interface (amplifier)? Disconnect the capsule and substitute with a quality (styrene, mica or good ceramic) capacitor of aproximately the same capacitance value and listen to the microphone output after placing it back into its housing to avoid masking by hum.

For dual diaphragm microphones this may require two capacitors, and using this substitution one side at the time even allows to identfy which side may be the cause.
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Uwe Sattler
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klaus

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #20 on: February 19, 2013, 05:38:15 PM »

Still a good testing method.

But some mic owners get nervous when their shaky fingers get close to a 6µ thin membrane that costs several hundred dollars to replace if they slip. So the breath test is a decent fallback.
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Klaus Heyne
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usattler

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #21 on: February 20, 2013, 08:44:43 AM »

The breath test does provide for a quick check without disassembly of the microphone, but is often limited value beyond revealing more than the presence of rogue static bias discharge through hygroscopic contamination. Working on and inside a valuable studio microphone should not be for anyone with shaky hands to begin with. No reasonable technician should attempt soldering at the leads close to the diaphragm, but rather at their far end...
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Jim Williams

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #22 on: February 20, 2013, 11:51:50 AM »

Use that pad to determine where the problems lie. If the problems are attenuated by the use of the pad switch, (-20 db in a B-ULS) then it's located in the head amp before the filter section. That does locate the problem on one of the two pcb's.

My experience with these mics is the most likely components to fail are the tantalum caps in the power supply circuits. Always check the power rails first on these mics first or you may be following a false trail.
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mike zietsman

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #23 on: February 28, 2013, 10:14:28 AM »


My experience with these mics is the most likely components to fail are the tantalum caps in the power supply circuits. Always check the power rails first on these mics first or you may be following a false trail.


After replacing all of the tantalum capacitors in my eb I am still getting a reduced voltage to the capsule (I think it was about 40v instead of 60v) which my tech suspects might be because of his multi meter not being able to measure accurately in the part of the circuit that has such a high impedance - does that sound logical?

Also - I am getting a lower output from my eb than I am from a friends eb p48 - about 6 or so db and I would have thought it would be the other way around because of the relatively lower voltages being fed to the capsule on the eb p48. Is that normal?


Thanks,
Mike
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Jim Williams

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #24 on: February 28, 2013, 10:48:16 AM »

Measure the oscillator output before the series resistors, those are large values and will attenuate the voltage from a high impedance. Most DVM's are 20 meg ohms or less input impedance so they will show a lower reading if you measure after those series resistors on the output of the oscillator.
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klaus

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #25 on: February 28, 2013, 01:52:24 PM »

Measure the oscillator output before the series resistors, those are large values and will attenuate the voltage from a high impedance. Most DVM's are 20 meg ohms or less input impedance so they will show a lower reading if you measure after those series resistors on the output of the oscillator.
This is good advice for measuring polarization voltage in high impedance sections of ALL condenser mics, not just this model.

These super-high-value resistors (up to 1gig or more) rarely fail, so measuring at their input, i.e. right before them, is a reasonably good way to ascertain that the proper polarization voltage gets into the section.
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Klaus Heyne
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J.J. Blair

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #26 on: March 04, 2013, 12:49:25 PM »

I would like to report that Harman/AKG does indeed do legacy repairs on 414EBs at their Northridge, CA location.  I just had two of mine of them fixed there (bad switches and one blown preamp), and they did a fantastic job.  They do not do capsule work, but options for that have already been discussed in this thread.
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Jim Williams

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #27 on: March 05, 2013, 11:52:52 AM »


I am getting a lower output from my eb than I am from a friends eb p48 - about 6 or so db and I would have thought it would be the other way around because of the relatively lower voltages being fed to the capsule on the eb p48. Is that normal?


Thanks,
Mike

No, that suggests a reduced polarization voltage. The P-48 model has no oscillator, it's like an original U-87 taking the phantom voltage to the capsule, at a reduced level. Usually it's around 42 volts or so after all the series resistors and such. That is why the P-48 414 is about 5 db less output than an older 414 EB. Those use the internal oscillator to raise the polarization voltage to 60~62 volts.
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mike zietsman

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #28 on: March 13, 2013, 05:39:33 PM »

No, that suggests a reduced polarization voltage. The P-48 model has no oscillator, it's like an original U-87 taking the phantom voltage to the capsule, at a reduced level. Usually it's around 42 volts or so after all the series resistors and such. That is why the P-48 414 is about 5 db less output than an older 414 EB. Those use the internal oscillator to raise the polarization voltage to 60~62 volts.

Hmmm.... after replacing every tantalum cap in the mic I am still getting a reduced voltage in my older eb (about 46volts measured just before the resistors before the capsule). Any other ideas about where I might look?

as always - thank you so much!

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klaus

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Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #29 on: March 13, 2013, 06:50:19 PM »

Do you get the same voltage (as a minus voltage) for the rear side (Figure eight)?
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Klaus Heyne
German Masterworks®
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