Telefunken U47 noise issue

[Biula]

Back in the 40's and 50's many German/Austrian/Swiss mic manufacturers used rectifiers that consisted of coated metal(steel?) squares stacked up. in their power supplies. These rectifiers worked well and were in some of the finest tube mics ever made, but, it would not take much moisture to make them corrode and fail(short). While it may be worthwhile to preserve totally original mics, in the interest of reliability, it is probably better to replace the whole power supply with an aftermarket supply, or at least have a spare one on hand. When you have session with 85 musicians coming in at union scale in NYC and have no spare M50's they probably need to work. Amazingly, as an emergency move, a high voltage modern diode will do in a pinch. The circuit design of these power supplies are pretty simple and conventional. Easy to understand and repair. Especially compared to modern switching supplies. (just throw it away and get a new one)but, original parts are almost impossible to find, like the V-14 tube. As a practical matter, modern components can successfully replace them. But, not all changes should be considered progress,

Maybe you are referring to selenium rectifiers... Well, as stated earlier:

I've serviced many original U47 and never had any issues with the NG PSUs. Even the selenium rectifiers seem to work forever.

So, better a well mainteined original power supply than an "aftermarket" one (BTW, Telefunken Elektroakustik crap power supply IS considered NG47 aftermarket substitute!!!), especially if you are dealing with such important events... if you do not trust an original NG47 how can you trust the venerable 1940 VF14? It was meant to work flawlessly for 10.000 to 20.000 hours, and so does its power supply.

 

[Biula]

And just to be clear, Telefunken Elektroakustik has nothing to do with the historical German brand: is an USA based company ( South Windsor, CT) which in 2001 aquired the right to use the name and logo (in North America) of the 1903 founded Telefunken AG, the real one (from 1967 acquired by AEG). Is interesting to know that in USA after the WWII Neumann brand was banned from the market due to suspect to have had Nazi connections; so Gotham, the American distributor, rebranded all their products as "Telefunken" (hence the "Telly" Sinatra mike...).

 

[Biula]

Don't be like that. Not everything Telefunken makes is bad, and expensive. It is just that everything is based on 120 years old heritage, German, American, Irish, who cares as long as it says 120 years old....

That's another company... Telefunken AG is part of the German industrial giant AEG since 1967, they surely make great home appliances and TV sets... no more expensive tube microfones!

 

[rock soderstrom]

Is interesting to know that in USA after the WWII Neumann brand was banned from the market due to suspect to have had Nazi connections; so Gotham, the American distributor, rebranded all their products as "Telefunken" (hence the "Telly" Sinatra mike...).

I'm not sure if that's true. Do you have any evidence for this statement?
I would be very interested in that. Like all companies in Germany during the second world war, Neumann was part of the system. There was almost no "non-war important" production during the “Totalen Krieg”, all economic enterprises were committed to the “Endsieg”.

But Neumann was a very, very small light, Telefunken was a zillion times bigger and way more important. If Neumann had been blacklisted after the war, why not Telefunken? Telefunken had countless divisions and sold pretty much everything for money.

I think that was simply a distribution issue, Neumann did not have the name, infrastructure and money for worldwide distribution at that time, Telefunken was much better positioned in that respect. Telefunken simply ordered microphones from Neumann to sell them worldwide for profit, classic OEM business as it is still practiced today.

That's another company... Telefunken AG is part of the German industrial giant AEG since 1967, they surely make great home appliances and TV sets... no more expensive tube microfones!

They are all gone - Telefunken, AEG and so on. The company posted by kingkorg has just as little to do with the original Telefunken AG as Telefunken USA. They have only licensed the name, too. There is actually a company here in Germany that specializes in sub-licensing well-known brand names from German history for money.

 

[Mihobro]

Harmonic elements may indicate excessive current draw, either due to short, in wiring or silicon, or supply cap that is leaking.

 

[Bonnie1]

And just to be clear, Telefunken Elektroakustik has nothing to do with the historical German brand: is an USA based company ( South Windsor, CT) which in 2001 aquired the right to use the name and logo (in North America) of the 1903 founded Telefunken AG, the real one (from 1967 acquired by AEG). Is interesting to know that in USA after the WWII Neumann brand was banned from the market due to suspect to have had Nazi connections; so Gotham, the American distributor, rebranded all their products as "Telefunken" (hence the "Telly" Sinatra mike...).

The Telefunken brand including diamond logo certainly has a storied history. In the late 80's AEG let the "Trademark" expire, and Oliver Archut applied for and received ownership of the "Trademark" in the USA. In 2001 Toni Fishman (RIP) purchased the "Trademark" from Oliver and that was the beginning of Telefunken Elektroakustik. The is a lot more to this story..... my attention is needed elsewhere.

-dmax
AMI/TAB-Funkenwerk

 

[amplexus]

Back in the 40's and 50's many German/Austrian/Swiss mic manufacturers used rectifiers that consisted of coated metal(steel?) squares stacked up. in their power supplies. These rectifiers worked well and were in some of the finest tube mics ever made, but, it would not take much moisture to make them corrode and fail(short). While it may be worthwhile to preserve totally original mics, in the interest of reliability, it is probably better to replace the whole power supply with an aftermarket supply, or at least have a spare one on hand. When you have session with 85 musicians coming in at union scale in NYC and have no spare M50's they probably need to work. Amazingly, as an emergency move, a high voltage modern diode will do in a pinch. The circuit design of these power supplies are pretty simple and conventional. Easy to understand and repair. Especially compared to modern switching supplies. (just throw it away and get a new one)but, original parts are almost impossible to find, like the V-14 tube. As a practical matter, modern components can successfully replace them. But, not all changes should be considered progress,

Ahh yes. Those selenium rectifiers that would fill the room with toxic rotting horseradish smelling smoke when they failed and are now considered hazardous waste?

I’ll stick with silicon and a dropping resistor.

 

[lunatic_ash]

Hey buddies, I will tell you the result.
I sent the EQ pic and audio samples and talked with Telefunken a lot, and we concluded it was an issue related to the ground loop.
Yesterday, I visited my friend's studio and had a recording session with my mic
As Telefunken technicians had expected, the 120Hz noise was totally gone.
It's not an issue of the microphone system itself.

 

[RuudNL]

As was to be expected...

 

[Cqwet Dbdfte]

Hard grounding/bonding signal ground to cases is of questionable value.
Lifting ground temporarily for testing is ok but not permanently.
Using a 25A+ bridge rectifier (+- shorted) between power company safety ground and equipment ground can be used, bypassing the AC path with HF value cap and a megohm resistor.
This puts a couple of volts between signal ground and AC power ground.
The bridge rectifier should have enough capability to open the breaker.
Peak pulse current of rectifiers can be located in datasheet. Usually several hundred ampere.

Chasing ground loops is not fun. The effect would be line frequency "hum". "Noise" is usually referred to as random noise. Rectifier noise is twice line frequency, and have s lot of harmonics.
This would point more towards equipment issues.
Hum can also be induced magnetically, transformer to transformer, besides ground loops.
Just some things to keep in mind.

 

[Khron]

Well, especially since this is a tube mic, with its own (earthed) power supply, the ground connection to the preamp input is not necessary.

For example, the PSU of my Cad Trion 8000 actually has a "gnd lift" switch next to the output XLR, likely for just such scenarios.

 

[lunatic_ash]

Hard grounding/bonding signal ground to cases is of questionable value.
Lifting ground temporarily for testing is ok but not permanently.
Using a 25A+ bridge rectifier (+- shorted) between power company safety ground and equipment ground can be used, bypassing the AC path with HF value cap and a megohm resistor.
This puts a couple of volts between signal ground and AC power ground.
The bridge rectifier should have enough capability to open the breaker.
Peak pulse current of rectifiers can be located in datasheet. Usually several hundred ampere.

Chasing ground loops is not fun. The effect would be line frequency "hum". "Noise" is usually referred to as random noise. Rectifier noise is twice line frequency, and have s lot of harmonics.
This would point more towards equipment issues.
Hum can also be induced magnetically, transformer to transformer, besides ground loops.
Just some things to keep in mind.

Thanks, but sorry. I don’t read your comments..

When I asked you somethin’, you didn’t answer anything related to it and you just have talked about something that you wanna disgorge

Thanks for your time, but.. umm.. just for your time

 

[Cqwet Dbdfte]

Thanks, but sorry. I don’t read your comments..

When I asked you somethin’, you didn’t answer anything related to it and you just have talked about something that you wanna disgorge

Thanks for your time, but.. umm.. just for your time

That's OK. Glad you got help figuring out a most basic problem.
My answers could be useful to more (technical) people, and question like "Are there some cases that those capacitors have problems?" are impossible to answer.

 

[nielsk]

It is not unusual for mics with power supplies to introduce ground loops.
A simple pin 1 lift barrel to plug inline on the mic cable is useful here, as you really do not want to lift the power ground on the power supply.
There is no need for a pin 1 connection at the power supply audio output XLR if the power supply is properly grounded via it's power cord.
Some have installed a pin 1 lift switch in the power supply for this purpose.

 

[Khron]

There is no need for a pin 1 connection at the power supply audio output XLR if the power supply is properly grounded via it's power cord.
Some have installed a pin 1 lift switch in the power supply for this purpose.

Well, especially since this is a tube mic, with its own (earthed) power supply, the ground connection to the preamp input is not necessary.

For example, the PSU of my Cad Trion 8000 actually has a "gnd lift" switch next to the output XLR, likely for just such scenarios.

And what had I said?