AKG C414 XLS pulsating pop noize

[saint gillis]

I have a new C414 (XLS), it has a little pulsating popping noize, random, something like 1Hz or a bit less. Sometimes it stops, but not for very long.
When we switch from cardioid to super-cardioid or "8" the frequency becomes faster for 3s then it becomes ~1Hz again.

Anyone familiar with this problem?


Looks like I'm not the only one : https://gearspace.com/board/so-much...elp-akg-c414-xls-heartbeat-noise-problem.html
I cleaned all the headers contacts, reworked few parts, didn't help, I'd like to avoid stupidly replacing all the electrolytics, but without a schematic it's not easy.

 

[saint gillis]

There's is one electrolytic filtering capacitor (positif lead grounded) that is supposed to receive a negative voltage and has about +2.5V, this is not normal, but without the schematic of the XLS version that will not be easy to fix, and AKG support seems uneasy to reach..

 

[Tubetec]

Put the mic in a warm place for a few days , you can also place the mic in a zip locked bag with silica gel sachets ,
these mics run more or less cold to the touch , that means your breath can condense on the capsule .

 

[saint gillis]

Put the mic in a warm place for a few days , you can also place the mic in a zip locked bag with silica gel sachets ,
these mics run more or less cold to the touch , that means your breath can condense on the capsule .

Are you sure? the description of the issue doesn't sound like capsule related

 

[Tubetec]

Any random noise that comes and goes could be the capsule ,
either way drying or warming the mic costs nothing and doesnt risk any damage ,If pulling and hauling out components randomly seems like a better idea to you , off you go .

 

[saint gillis]

Of course not, but a positive voltage on a capacitor pin that is supposed to receive a negative one doesn't look like something that will be solved by drying the mic..

 

[saint gillis]

So drying the mic didn't help.
And trying to reach AKG support was a nightmare, AKG tells to contact Harmann, and Harmann says you need to get in touch with AKG, in circles...

 

[Glenn Wardle]

This is a long shot, but have you measured the phantom power feed. Is it stable, and does the issue happen on more than one make of preamp?
My reason to ask is that although the official spec for phantom power is 48 Volts via 6.8k, many inputs now 'simulate' this and drop the voltage as the current load increases as this makes the phantom power feed more energy efficient, but it could be the loading characteristics of the mic don't like the dynamic phantom power voltage modulation. Am I right in thinking the XLS has LEDs on it? If this is the case, then the mic itself might also use a small switch mode PSU to derive the feed voltage for the LEDs (and I assume a small micro) and I could well see an opportunity for compatibility issues when a dynamically servo controlled phantom power supply is feeding a dynamically variable load.

 

[saint gillis]

The phantom seemed sturdy..

The capacitor located just below the trimmer was receiving about 2.5V but in reverse polarity :


As it is almost impossible to retro-engineer this mic (4 layers pcbs), and as it was impossible to reach AKG support, I just decided to replace it and to reverse it..

Then I've read on another forum someone having the same kind of issue on a previous C414 version, he solved it bu replacing two 1µ tantalum caps.

Here are two yellow 1µ tantalum caps :


I've replaced them :




I'm still running tests over a long period of time, but it seems to work..

 

[saint gillis]

I forgot to mention, but the 220µ capacitor, the one below the trimmer, that was receiving a reverse voltage.
I've replaced it, put it upside down. The voltage over it takes ~5-10min to slowly rise to about 3V

 

[kags]

I’ve had similar wrestling matches with 414s and is a cleaning or connection/solder touch up didn’t solve the problem, I contacted Richard Land at Land Audio Services in Tennessee for advice and/or service. He is extremely knowledgeable in the 414s and probably a lot more…

 

[TLK]

One of my 414XLS mic had a frying and lo frequency rumbling that would appear after mic was powered up for a while. I had sent it to Harmon for repair, and although they did say the replaced a "wire" related to the capsule it did not fix the problem and it did not make sense that a wire would cause such an issue. Sending to them was a waste of time and money.. Since in these mics the various circuitry is connected together with header type pins and sockets, I took it apart and carefully cleaned all the pins & sockets with De-Oxit contact cleaner, put it back together and have never had the issue come back. If I recall, the capsule and pattern select switch board connects thru these header pins. With such a high impedance, anything related to connections for the capsule, capsule voltage biasing and first stages of circuitry, any oxidation could cause such a problem in my opinion.

 

[saint gillis]

Re-tried it today, problem re-appeared..
I did clean the pins and headers, I'm gonna do it again

 

[saint gillis]

Same pbm again after a deep cleaning
Especially when I switch from cardioid to hyper-cardioid or 8-fig, the "pop-pop" gets quicker for a while "pop-pop-pop-pop-popopopopop"

 

[TLK]

Have you tried testing the main board all by itself itself without the capsule and pattern selector connected simply by plugging in the XLR to your mixer and giving it a listen ? See if you still hear what you describe. Perhaps it's indeed a problem on the main circuit board you are chasing down..