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1
Klaus Heyne's Mic Lab / Re: Neumann reissues the U67
« Last post by klaus on Today at 03:11:05 am »
I meant the voltage coming out of the wall.
2
Klaus Heyne's Mic Lab / Re: Neumann reissues the U67
« Last post by aremos on Yesterday at 05:18:47 pm »
...
Have you checked the AC at the plug where you connect the power supply?

Yes. Haven't had any problem with anything else plugged into it (including a C-800G & REDD mics).
3
Klaus Heyne's Mic Lab / Re: Neumann reissues the U67
« Last post by klaus on Yesterday at 01:58:30 pm »
When I will review the mic (as soon as VK has a spare to send me), I will look at this issue.

My suspicion: it's the same issue I had once with an M150 power supply of similar construction: A Chinese-made AC-DC converter is embedded in the supply, similar to what a wall wart does, and it shut down (a type of circuit breaker senses overheating or other maladies) until it recovered. I replaced the converter (a third-party item that can be found on eBay) and the problem never reoccured.

Have you checked the AC at the plug where you connect the power supply?
4
Klaus Heyne's Mic Lab / Re: Neumann reissues the U67
« Last post by aremos on Yesterday at 01:43:08 pm »
Now you have 2 power supplies and can switch to find out if the problem follows the microphone or the PSU -  if the problem reappears at all.
Does this problem show up when you plug the PSU into a certain wall outlet or use a certain power cable?

The same issue occurred one month apart, in the exact same way, with completely different units!
It's as if both mics (along with a different PS, different mic cable, different PS cable) had to go through some type of "settling in"?
All of a sudden, after powering up for the first time & 1.5-2 hours of working perfectly & sounding fine, the same hum started emitting & no signal being able to be recorded. After shut-off (1/2 hour) & then powering up again the mics have been working fine.

The odds of this happening only to me must be astronomical, unless it's something common. Hence why am asking & very curious if it's happened to anyone else.
5
Klaus Heyne's Mic Lab / Re: Neumann reissues the U67
« Last post by Kai on Yesterday at 12:53:52 pm »
Now you have 2 power supplies and can switch to find out if the problem follows the microphone or the PSU -  if the problem reappears at all.
Does this problem show up when you plug the PSU into a certain wall outlet or use a certain power cable?
6
Klaus Heyne's Mic Lab / Re: Neumann reissues the U67
« Last post by aremos on May 22, 2018, 06:53:50 pm »
I just received my second U67 reissue & the EXACT same thing as the first one (received 13 APR) happened!:
After 1+ hours of recording the mic started with a hum & no signal coming in! Turned it off for 1/2 hour then turned it back on & has been working so far.
The first one has been working fine since that happened.

Has anyone else had this problem?
7
Klaus Heyne's Mic Lab / Re: Neumann U77 supply voltage for FET
« Last post by uwe ret on May 21, 2018, 03:12:35 pm »
Expect around 13 to 15 V across C109.
8
Klaus Heyne's Mic Lab / Re: KK54 New Vs Old
« Last post by klaus on May 20, 2018, 01:05:55 pm »
There are no precise dates of transition and quantities available. The closest I can come to the truth:

After Neumann developed the K8x Mylar capsule family, the final few KM(2)54 were delivered with the new capsule. To link a capacitor capsule which is grounded on one side, these mics received a coupler ring between the amp body and the capsule head, to accommodate the circuitry of the KM54. This coupler was also retrofitted by the Neumann service center in Berlin to any earlier KM54 whose nickel capsule failed, and which were fitted with the new KK84.

In my chronology based on data I have collected over the years, only a very few KM54 were made after January 1964. These received the then new KK64/74/84 (Mylar capsule plus coupler ring).

Put simply: any of the few KM54 issued after 1964 would have the Mylar KM8x capsule system and the coupler ring.
9
Klaus Heyne's Mic Lab / Neumann U77 supply voltage for FET
« Last post by RuudNL on May 20, 2018, 07:11:51 am »
I would like to know (just to check) what the supply voltage for the FET stage in a Neumann U77 should be.
More specific: the voltage over C109.
This voltage is generated by the DC/DC converter.
Any thoughts?
10
Klaus Heyne's Mic Lab / KK54 New Vs Old
« Last post by Djembe on May 20, 2018, 06:19:11 am »
Did Neumann produce a later version of the KK54 that looked like a KK84?
If so, what is the difference in sound?
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