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 91 
 on: November 13, 2017, 01:08:21 pm 
Started by sonicdogg - Last post by Jim Williams
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.

 92 
 on: November 12, 2017, 08:11:21 pm 
Started by sonicdogg - Last post by sonicdogg
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.

 93 
 on: November 12, 2017, 12:23:14 pm 
Started by SDVIG - Last post by klaus
I am dubious that the original electrolytic 0.5mfd cap is your problem. It never has, during all my years of attending to U67. But there could of course always be a first.

Did you measure it outside the circuit? Every half-decent meter these days has a capacitance tester built in. I want you to conform that it measures low before you move on.

As to voltages in a replacement: You can safely install a film & foil polypropylene capacitor with 0.5mfd capacitance and 200VDC rating, as long as it fits. I would not use inferior material in this position as it's decoupling DC from audio going into the transformer.

 94 
 on: November 12, 2017, 12:14:24 pm 
Started by sonicdogg - Last post by klaus
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

 95 
 on: November 12, 2017, 12:01:54 pm 
Started by sonicdogg - Last post by sonicdogg
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.

 96 
 on: November 12, 2017, 10:49:14 am 
Started by sonicdogg - Last post by Kai
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.



 97 
 on: November 12, 2017, 07:56:51 am 
Started by SDVIG - Last post by SDVIG
Dear Claus.

I am very grateful to you for your help.
Your advices help me a lot.

I want to ask you a question about the problem with my microphone U67. I'm familiar with a skilled craftsman. He is known as one of the best masters in musical audio equipment. For example, it can parse and compile SSL 4000. But he is not a specialist in microphones. Now to the point. I feel my microphone is losing the low end. The master tells me that the capacitor C9 is responsible for this. When we extracted it from the microphone, the capacity was normal(Capacitance is OK). But the master does not have a stand in order to test this capacitor. If we did not have a capacitor of a suitable size, we put two capacitors with a superior capacity of 4 times. These capacitors have a voltage of 200 volts. Master said that this is dangerous for the microphone. With the audio test, the microphone received a low end, but the sound turned out to be harsh. Please advise which film capacitor should be placed in the microphone?
At the second edition of U67, Neumann used film capacitors.


I see such suggestions on Ebay:

MKC 1860 250V 0.47uF 474 10% HV Non-polar Film Capacitor:
https://www.ebay.com/itm/1lot-6PCS-ERO-MKC-1860-250V-0-47uF-474-10-HV-Non-polar-Film-Capacitor/181834945143?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649


 CAP, FILM, PET, 470NF, 250V, AXIAL MKT1813447255G By VISHAY
https://www.ebay.com/itm/1-X-CAP-FILM-PET-470NF-250V-AXIAL-MKT1813447255G-By-VISHAY/192229054155?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649


1. Could you advise me how to act?
2. Why is the U67 Schematic talking about 250 volts, but in reality I saw in several microphones 350 volts?
3. Maybe it's not a condenser?


PS: Any advice is welcome.

Second edition of U67: & My capacitor:

 98 
 on: November 12, 2017, 03:14:40 am 
Started by klaus - Last post by klaus
(...) when we make a music recording we leave it to the brain of the unknown listener at home to do the interpreting.

In the field of analyzing any of the five senses, there is no reality outside subjective interpretation. So, objectively, nothing happens acoustically beyond and outside of sound reaching us and having an effect on us.

We continue to TRY correlating sound we hear to sound waves we measure, but that is only valid to the extent that it would allow us to identify specific measurable features of sound waves (like gross frequency anomalies) that we can correlate to dissatisfying sound and try to correct and improve it: listening is the corrective, nothing else.

The idea that certain idealized properties of measurements, like a ruler-flat frequency response, would get us closer to satisfying sound remains unprovable. So far, we can only verify by listening whether manipulating parameter x or y just got us closer to an aurally satisfying experience.

Quote
(...) we were discussing just the microphone as a transducer (and I guess the associated preamp) and its accuracy.

 'Accuracy' of a microphone can only be judged by hearing the musical event live, and comparing how close (accurate) the recording of that event comes to that experience. A determination of accuracy can therefore never be derived from any other (non-sensual) experience or method, see above.

Regarding the relatively primitive nature of microphones, even the best ones, compared to our hearing apparatus, I never get tired of citing this example:

Sitting in an auditorium, and listening to a quiet passage of the orchestra, I can tune out the noise of the person sitting next to me rustling her candy wrapper. If I were listening to a recording of this event with a microphone placed where my ear is, I would be royally annoyed by the disturbance.
The brain can analyze sound waves delivered from the ear's sophisticated pathways, and filter out unwanted noise. The relatively primitive rendering of reality by a microphone does not make this possible.

 99 
 on: November 12, 2017, 02:02:01 am 
Started by sonicdogg - Last post by sonicdogg
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.

 

 100 
 on: November 11, 2017, 09:29:51 pm 
Started by sonicdogg - Last post by uwe ret
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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