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Author Topic: AKG 414EB Picking Up Radio  (Read 576 times)

sonicdogg

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Re: AKG 414EB Picking Up Radio
« Reply #15 on: November 11, 2017, 04:53:09 am »

Sorry if I wasn't clear. Of course the connector !     My test cable is the UP OCC cable built by Charles @ Cathedral Pipes. I believe it is 2 conductor with a braided shield. Sorry if I didn't answer your question properly. Not my intention to cause frustration.  The problem, however, does not lie within the cabling. I have several condensers that would exhibit at least a proportional amount of noise attributed to their sensitivity, and none have ANY noise with ANY cable I use. 
 
Thanks for your help. I appreciate it and the effort. It is somewhere within the mic and its components. I'm scientific enough to test things completely and rule out things that are not cause for failure or problems. 35 years as a class A electrician taught me a lot about finding causes. I was hoping for an insight by asking my question here.
 
The post by Mr. Kai is the right course of action for me at this time. Thanks very very much.
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Jim Williams

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Re: AKG 414EB Picking Up Radio
« Reply #16 on: November 11, 2017, 01:35:55 pm »

Beginning to suspect a broken FET. Although the mic does work and without the RF would be an excellent addition to the collection. 

Keep in mind a jfet transistor does not rectify a signal like the base of a bipolar transistor can. It's very unlikey the jfet is rectifing rf unless the leads or solder connections are suspect. Was it replaced? If so, solder flux or remaining dirt may be a cause.

Or maybe the ^Russians^?
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klaus

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Re: AKG 414EB Picking Up Radio
« Reply #17 on: November 11, 2017, 02:24:46 pm »

No, it's not in the wiring. No, it's not the cable, it is this mic and ONLY this mic. I have a lot of mics and NONE pick up radio in my room. 
 

Do you get the same amount of RF when you plug in the mic at someone else's place, in another building, another part of town with someone else's cable?
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Klaus Heyne
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sonicdogg

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Re: AKG 414EB Picking Up Radio
« Reply #18 on: November 11, 2017, 02:33:50 pm »

Do you get the same amount of RF when you plug in the mic at someone else's place, in another building, another part of town with some one else's cable?

 Yes. Simply.
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sonicdogg

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Re: AKG 414EB Picking Up Radio
« Reply #19 on: November 11, 2017, 04:50:02 pm »

Keep in mind a jfet transistor does not rectify a signal like the base of a bipolar transistor can. It's very unlikey the jfet is rectifing rf unless the leads or solder connections are suspect. Was it replaced? If so, solder flux or remaining dirt may be a cause.

Or maybe the ^Russians^?

 It's the government spying on me through my Austrian equipment....
 
 As to addressing this....I don't know what they replaced or repaired. I'm still looking for the paperwork. I talked with the tech who's name was 'Bob' (I think) and he was the one person who the repair department sent this mic to since he was the only one who had stockpiled parts for the EB and earlier 414's. I'm thinking he was going to retire around this time so reconnecting with his department might not be possible. It WAS AKG of some sort in the USA and if I could find the papers I would remember it better. This would have been in 2015.....I think. 
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Kai

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Re: AKG 414EB Picking Up Radio
« Reply #20 on: November 11, 2017, 07:19:10 pm »

The radio station is an FM station....strange.
Are you sure it's an FM station?
It's almost impossible to decode FM into something other then noise, with the few electronic parts that live inside a mic, even if one tried on purpose.
You need, basicly, a stable oszillator at about 100 MHz, tuned to the station, and more.
Decoding AM is simple, can be done with almost any single active device that has nonlinearity.
This is why the often very hot CB signals tended to creap into audio mixers.
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uwe ret

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Re: AKG 414EB Picking Up Radio
« Reply #21 on: November 11, 2017, 09:29:51 pm »

The interferance not changing with the microphone shielded by a metal can or when touching its housing to the connector shell leads me to believe the cable to be acting as an antenna for the offending radio signal, which then enters either the microphone, or the input pre-amplifier stages. Use of the Neutric EMC-series connectors should ameliorate or eliminate this problem. Additional RF-filter components (ferrite beads, choke coils, capacitors) at the microphone's output and/or the pre-amplifier's input are an alternative possible solution.
 
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sonicdogg

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Re: AKG 414EB Picking Up Radio
« Reply #22 on: November 12, 2017, 02:02:01 am »

Are you sure it's an FM station?
It's almost impossible to decode FM into something other then noise, with the few electronic parts that live inside a mic, even if one tried on purpose.
You need, basicly, a stable oszillator at about 100 MHz, tuned to the station, and more.
Decoding AM is simple, can be done with almost any single active device that has nonlinearity.
This is why the often very hot CB signals tended to creap into audio mixers.
 
I wasn't sure until a couple of days ago when I heard the call letters.
The interferance not changing with the microphone shielded by a metal can or when touching its housing to the connector shell leads me to believe the cable to be acting as an antenna for the offending radio signal, which then enters either the microphone, or the input pre-amplifier stages. Use of the Neutric EMC-series connectors should ameliorate or eliminate this problem. Additional RF-filter components (ferrite beads, choke coils, capacitors) at the microphone's output and/or the pre-amplifier's input are an alternative possible solution.
 
Thats one of the connector types in use here.

 
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Kai

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Re: AKG 414EB Picking Up Radio
« Reply #23 on: November 12, 2017, 10:49:14 am »

I still wouldn't bet that it's an FM station, but anyway:
- Make sure there are proper ground connections everywhere.
- Check all wire interconnects if nothing is loose.
- Test the switches, does the radio station go away with certain setting?
If yes, clean the switches.
On the audio board:
- Start by replacing all electrolytic and tantal caps, this should be done anyway.
- Next candidate is the FET, then the 2 bipolar transistors.
- While they're out you can check all the resistors for proper value.
- Replace ceramic caps.
- Check the film caps if you have a cap meter, specially those that are permanently in the audio path.


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sonicdogg

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Re: AKG 414EB Picking Up Radio
« Reply #24 on: November 12, 2017, 12:01:54 pm »

I still wouldn't bet that it's an FM station, but anyway:
- Make sure there are proper ground connections everywhere.
- Check all wire interconnects if nothing is loose.
- Test the switches, does the radio station go away with certain setting?
If yes, clean the switches.
On the audio board:
- Start by replacing all electrolytic and tantal caps, this should be done anyway.
- Next candidate is the FET, then the 2 bipolar transistors.
- While they're out you can check all the resistors for proper value.
- Replace ceramic caps.
- Check the film caps if you have a cap meter, specially those that are permanently in the audio path.

 I thought it was weird to be picking up FM radio too, but the fact is, it is a station I regularly listen to....101.7 KINK in Portland where I live. I had not heard the call letters until a couple of days ago. The fact that the interference is strong enough to make out this makes the mic unusable.
 
 I truly believe there is a ground lifted somewhere in this mic. When it came back from repair and started this nonsense I opened it up and the grounding strap was basically unscrewed. This cut the signal problem in half and now I'm looking for the other half.
 
 I haven't found a loose connections other than that one at this time.....that doesn't mean there isn't one.

 No difference in switch settings.
 
 I'm taking it to a friends bench where there are the proper testing devices and we'll go from there.
 
Thanks.
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klaus

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Re: AKG 414EB Picking Up Radio
« Reply #25 on: November 12, 2017, 12:14:24 pm »

If you cannot get this resolved, and as you live close by and I also can receive KINK over the airwaves, I am willing to take a look at it (no, not a paid job, just curiosity).
KH
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Klaus Heyne
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sonicdogg

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Re: AKG 414EB Picking Up Radio
« Reply #26 on: November 12, 2017, 08:11:21 pm »

If you cannot get this resolved, and as you live close by and I also can receive KINK over the airwaves, I am willing to take a look at it (no, not a paid job, just curiosity).
KH

 Thanks Klaus.
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Jim Williams

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Re: AKG 414EB Picking Up Radio
« Reply #27 on: November 13, 2017, 01:08:21 pm »

One band-aid approach is to use a couple of those snap on ferrite bead cores in the plastic box and place them over the mic cable as it exits the XLR connector. That should remove the cable/contacts from the equation.
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klaus

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Re: AKG 414EB Picking Up Radio
« Reply #28 on: November 13, 2017, 01:39:36 pm »

Band aid, indeed. I am always more intrigued by removing the cause, rather than add layers of gauze.
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Klaus Heyne
German Masterworks
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