Original U67 and 62Hz noise

[jandoste]

Hi Guys,
I have an original U67 and I'm getting a hum noise with this baby! All mike V values are good but I'm not sure if its PSU is ok... Do you have any idea on this issue? this noise is on prox 62 Hz....

Thank you

Jan

 

[PRR]

62 is so strange.

Strange for 60Hz lands, and even stranger if you are in a 50Hz land.

If it really IS 62Hz, I would look at PC monitors and such which might run on odd rates.

 

[jandoste]

Thanks PRR.
I'm checking the PSU and it might an issue on PSU's trax.... I have 117V which is good and 220V is 0( wrong) and 127V is 107 V( must be 127V)
and I see everywhere 32V.... so Do you think Tranx is dead or just a resistor makes things strange?

Thank you

Jandoste

 

[radardoug]

Do you know what you are doing? Doesn't sound like it.
If the voltages out to the mike are correct then your problem is not the supply.
How is the grounding arranged? The Neumann supply has options for the internal grounding.
Get hold of a circuit, there are plenty on the web.

 

[Pip]

Do you know what you are doing? Doesn't sound like it.
If the voltages out to the mike are correct then your problem is not the supply.
How is the grounding arranged? The Neumann supply has options for the internal grounding.
Get hold of a circuit, there are plenty on the web.

Ouch! IMO the first part of your reply is not helpful in trouble shooting but maybe I'm wrong. If you can be helpful please help this person as they are obviously trying to learn more than they know. I agree that the frequency you put forward to be the problem sounds like some sort of inductive thing not a failed circuit issue.

 

[Whoops]

Do you know what you are doing? Doesn't sound like it.
If the voltages out to the mike are correct then your problem is not the supply.
How is the grounding arranged? The Neumann supply has options for the internal grounding.
Get hold of a circuit, there are plenty on the web.

Ouch! IMO the first part of your reply is not helpful in trouble shooting but maybe I'm wrong. If you can be helpful please help this person as they are obviously trying to learn more than they know. I agree that the frequency you put forward to be the problem sounds like some sort of inductive thing not a failed circuit issue.

Hi
I dont think the first part of the reply was meant in a bad way , it was an honest and worried question by Radardoug  because we are talking about some dangerous voltages inside the U67 PSU, and we are talking about a really expensive microphone that it's not produced for a long time.
It's not a work that should be done by a beginner, there's other projects to learn, grow and gain more experience.
Not that I'm saying Jandoste is a beginner, I don't know, but like Radardoug by the type of questions and comments I also had the same feeling.

Jandoste here is the best help I think I can give you,
you have an amazing microphone with you, it's value is quite high, and even higher if well maintained and repaired properly, so it's  convenient to take it to someone experienced in repairing Neumann microphones.
Please take it to a qualified tech, you will not be sorry and it will be worth every penny for you.

 

[jandoste]

Honestly his response doesn't help! I know what I'm doing but I'm asking what I don't know...  That's it!
Ok I don't need any help guys! I just want to say Thanks PRR for trying helping me.

Jnadoste

Do you know what you are doing? Doesn't sound like it.
If the voltages out to the mike are correct then your problem is not the supply.
How is the grounding arranged? The Neumann supply has options for the internal grounding.
Get hold of a circuit, there are plenty on the web.

Ouch! IMO the first part of your reply is not helpful in trouble shooting but maybe I'm wrong. If you can be helpful please help this person as they are obviously trying to learn more than they know. I agree that the frequency you put forward to be the problem sounds like some sort of inductive thing not a failed circuit issue.

Hi
I dont think the first part of the reply was meant in a bad way , it was an honest and worried question by Radardoug  because we are talking about some dangerous voltages inside the U67 PSU, and we are talking about a really expensive microphone that it's not produced for a long time.
It's not a work that should be done by a beginner, there's other projects to learn, grow and gain more experience.
Not that I'm saying Jandoste is a beginner, I don't know, but like Radardoug by the type of questions and comments I also had the same feeling.

Jandoste here is the best help I think I can give you,
you have an amazing microphone with you, it's value is quite high, and even higher if well maintained and repaired properly, so it's  convenient to take it to someone experienced in repairing Neumann microphones.
Please take it to a qualified tech, you will not be sorry and it will be worth every penny for you.

 

[Whoops]

Honestly his response doesn't help! I know what I'm doing but I'm asking what I don't know...  That's it!
Ok I don't need any help guys! I just want to say Thanks PRR for trying helping me.

Jnadoste

Hi Jandoste,
we are all trying to help you, and being humble is the best way to learn and receive help.

If you are experienced then you know that if you measure voltages probably is not a transformer fault (probably!),
and also that voltages in this PSU have to be measured with the Microphone connected to the PSU and with the Tube in place, because you need the proper load from the microphone otherwise voltages can be way off.
Also there's a input voltage switch on this PSU, and it should be set for your country mains, if you are in Europe should be set to 240v.
Hum in audio could also be related to bad filtering in the PSU, and bad filtering in the PSU could be related to bad Electrolytic capacitors.  If the PSU has the original caps they probably need to be replaced for new ones.

The search function on this forum and google is also your friend, there's a lot of different valuable threads on the subject, and the U67 Mic and PSU schematic is easily available on the net.

But really the best help, if you're not familiar with any of this is to take the Neumann U67 Microphone and PSU to a qualified Technician. It's always a great decision.

 

[radardoug]

The NU67 does not have a mains selector switch. It has screws and a link on the pcb. It also has links that allow the grounding to be re-arranged. Working on this supply is dangerous, lots of exposed high voltage. The OP said he had 62 Hz hum. Mains frequency is normally 50 or 60 Hz. So if it is mains related it should be one of these frequencies, or harmonics. Power supply hum is normally at the 2nd harmonic, as most supplies use full wave rectification.
This is a valuable microphone. If you are not qualified to repair it, dont try! You may wreck the microphone.

 

[Whoops]

The NU67 does not have a mains selector switch. It has screws and a link on the pcb. It also has links that allow the grounding to be re-arranged. Working on this supply is dangerous, lots of exposed high voltage. The OP said he had 62 Hz hum. Mains frequency is normally 50 or 60 Hz. So if it is mains related it should be one of these frequencies, or harmonics. Power supply hum is normally at the 2nd harmonic, as most supplies use full wave rectification.
This is a valuable microphone. If you are not qualified to repair it, dont try! You may wreck the microphone.

Thanks Radardoug, for "main selector switch" I  wanted to say "It has screws and a link on the pcb" to select the input voltage.

"This is a valuable microphone. If you are not qualified to repair it, dont try! You may wreck the microphone."

 

[moamps]

Thanks PRR.
I'm checking the PSU and it might an issue on PSU's trax.... I have 117V which is good and 220V is 0( wrong) and 127V is 107 V( must be 127V)
and I see everywhere 32V.... so Do you think Tranx is dead or just a resistor makes things strange?
Jandoste

You are obviously measuring transformer primary windings voltages versus ground with flipped mains connector. The readings are OK.
Please use NU67 schematic and measure +210V(pin 5) and 6,3V (pin4) points to GND (pin 7) while microphone is connected to PSU.
Measure those using DVM set to DC and AC, so we can decide are the voltages correct.
You are working with high voltages on expensive microphone (cca 10000USD) so be very very careful.