Telefunken U47 noise issue

[lunatic_ash]

I bought a brand new Telefunken U47 from the official dealer in April 2024.

As you know, it’s a super expensive mic, so I’ve used it with extra care. There is no damage at all, and the moisture levels are perfectly controlled with the moisture control cabinet.

I used it without any problem, but today I could hear a slight but noticable noise. (It’s not a popping noise. It’s steady)

I turned the power supply unit off and on, and it disappeared. However, after few hours of recording, it occured again.



You can see the noise around 120hz

I have an important recording schedule and I’m waiting after sending an email to Telefunken now, but wanna hear your cases before I get a reply from Telefunken.

If I had bought used one, I could think it’s time to replace the vacuum tube.
However, I bought a brand new one in April!

If you wanna listen to how it sounds, I will upload it too.

Really need your helps!

 

[thomasdf]

probably 60hz power supply harmonics hum.
Considering the price of such a microphone, don’t think twice and get in touch with Telefunken or your reseller before attempting anything, it feels like you are not the best person to fix it, no offense.
I also think / hope that with such premium price you can get a replacement mic while yours is being fixed.
Considering dropping by the presentation section, too, if you want to get involved in the forum life
Cheers

 

[Khron]

You can see the noise around 120hz

At about -87dBFS?

 

[lunatic_ash]

probably 60hz power supply harmonics hum.
Considering the price of such a microphone, don’t think twice and get in touch with Telefunken or your reseller before attempting anything, it feels like you are not the best person to fix it, no offense.
I also think / hope that with such premium price you can get a replacement mic while yours is being fixed.
Considering dropping by the presentation section, too, if you want to get involved in the forum life
Cheers

Thanks for your reply As you told me, I won’t do anything to fix it
The question is that I had used it with no problem for 4 months, but why it happened suddenly?

 

[lunatic_ash]

At about -87dBFS?

Yeah originally there is no noise like that.

 

[pasarski]

Could it be some other PSU nearby causing it?

 

[RuudNL]

Do you have a sound sample? That would probably give an idea of the origin of the disturbance.

 

[lunatic_ash]

probably 60hz power supply harmonics hum.
Considering the price of such a microphone, don’t think twice and get in touch with Telefunken or your reseller before attempting anything, it feels like you are not the best person to fix it, no offense.
I also think / hope that with such premium price you can get a replacement mic while yours is being fixed.
Considering dropping by the presentation section, too, if you want to get involved in the forum life
Cheers

https://repforums.prosoundweb.com/index.php?topic=23670.0

I googled a lot and found the post about the same issue. They said it is probably Electrolytic caps problem.

However, I will do nothing until I get a reply from Telefunken if it’s just a tiny problem, I will visit audio repair shop to replace capacitors.

 

[lunatic_ash]

Could it be some other PSU nearby causing it?

Maybe not. I also check the whole things around, but thanks for your opinion!

 

[lunatic_ash]

Do you have a sound sample? That would probably give an idea of the origin of the disturbance.

I will upload it soon! But before that, if you wanna read about the same issue, plz check this link below

https://repforums.prosoundweb.com/index.php?topic=23670.0

I just found it.

 

[RuudNL]

A defective capacitor is not the first thing I think of, especially after such a short time. In addition, today's electrolytic capacitors are considerably more reliable than the capacitors in the 1960s, when the U47 just came onto the market.

 

[lunatic_ash]

A defective capacitor is not the first thing I think of, especially after such a short time. In addition, today's electrolytic capacitors are considerably more reliable than the capacitors in the 1960s, when the U47 just came onto the market.

Anyway, I wanna let you hear the noise, but it works perfectly now. I can’t record it
So embarrassing.

 

[Khron]

Wonky ground contact somewhere?

 

[Spencerleehorton]

Yeah or something plugged into the same power source or extension lead

 

[Biula]

Wonky ground contact somewhere?

No, if is 120Hz is generated internally after the bridge rectifier... definitively a filtering condenser related issue, an external induced ground issue would be 60Hz (50Hz in Europe). The best method to check it is to switch off momentarily the power supply: for some seconds the microfone still continues working, due to the long capacitors discharging time, and the issue might be gone if the problem is an internal component. Eventually it come back switching on again.

 

[Cqwet Dbdfte]

EMI/RFI, shielding, decoupling, ground loops, contact issues, faulty or "weak" equipment downstream?
Old equipment designed in the pre-cellphone era have the potential of RF susceptibility.
Possibilities abound.

 

[lunatic_ash]

No, if is 120Hz is generated internally after the bridge rectifier... definitively a filtering condenser related issue, an external induced ground issue would be 60Hz (50Hz in Europe). The best method to check it is to switch off momentarily the power supply: for some seconds the microfone still continues working, due to the long capacitors discharging time, and the issue might be gone if the problem is an internal component. Eventually it come back switching on again.

Yes, you are right. Following the method you told me, it’s gone after turning off the power supply while the mic is still working for 2-3 seconds.

As I posted before, someone said the problem is electrolytic capacitor on the similar case(124hz hum noise)

https://repforums.prosoundweb.com/index.php?topic=23670.0

I’m still waiting for a reply from Telefunken, and I’m gonna visit an audio repair shop next week, but If I show you the inside of the power supply, can you recognize what the filter capacitors are?

Actually I bought a brand new mic, and I’ve been using with great care. I totally don’t why this kinda thing happen.

I also wanna know why it works perfectly fine now, but sometimes that hum noise occurs again.

 

[Cqwet Dbdfte]

The orginal U47 did not have much in the way of RFI mitigation like some later mikes had.
How good is the intermetallic connection between the head basket and the mike body? The multiconductor cable did not have any RF chokes at either end, etc.
I doubt the design would pass any recent EMI specs.
Even if the tube circuit is not very efficient at RF, it may be sufficiently "good" at passing along annoyance levels.
The powersupply has three cords attached, that should be the first place to fit with RFI suppression.

 

[Khron]

Actually I bought a brand new mic, and I’ve been using with great care. I totally don’t why this kinda thing happen.

Just because it's new and expensive, doesn't mean there were no corners cut anywhere. Company profits gotta come from SOMEwhere ..

 

[Cqwet Dbdfte]

Old designs may have their charm but interfacing new realities may incur new "corners".