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1
Klaus Heyne's Mic Lab / Re: Neumann U77 supply voltage for FET
« Last post by uwe ret on Today at 03:12:35 pm »
Expect around 13 to 15 V across C109.
2
Klaus Heyne's Mic Lab / Re: KK54 New Vs Old
« Last post by klaus on Yesterday at 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.
3
Klaus Heyne's Mic Lab / Neumann U77 supply voltage for FET
« Last post by RuudNL on Yesterday at 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?
4
Klaus Heyne's Mic Lab / KK54 New Vs Old
« Last post by Djembe on Yesterday at 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?
5
Klaus Heyne's Mic Lab / Re: So, What's That All About?
« Last post by mikezietsman on May 19, 2018, 01:13:02 am »
Having been in studio sessions with camera guys there is also a fairly good chance the engineers told the team they were off to lunch and the photographer set the shots up with absolutely no regard for the way the mics were setup.
6
Klaus Heyne's Mic Lab / Re: So, What's That All About?
« Last post by Dominick Costanzo on May 18, 2018, 09:39:27 pm »
FAME Studios in Muscle Shoals 1967, not Columbia NYC. By 1967 when this session occured, that shock mount had very likely seen lots of use. I've dealt with more than a few 47 shock mounts where the adhesive holding the felt to the ring gave out. Be that a diaper or foam, it didn't hurt the music.
7
Klaus Heyne's Mic Lab / Re: Neumann km54 faulty
« Last post by klaus on May 18, 2018, 08:41:31 pm »
Now that you confirmed that the mic is c-cathode biased, I am not liking that low plate voltage you reported.

A defective tube will have a plate voltage that low. The fact that the frying sound is fairly constant and never goes away also would support a defective tube, at least as a secondary if not primary cause for your noise.

8
Klaus Heyne's Mic Lab / Re: Neumann km54 faulty
« Last post by fffaustino on May 18, 2018, 06:06:07 pm »
Many thanks Kai, Uwe and Klaus,

my mic is a km54a model converted to "c" (at least there is a c stamped following the "a").

I will do the breath test carefully and see what happen with the noise, i hope it is just a dirty capsule and it is possible to clean it..letīs see

thanks and best regards!
9
Klaus Heyne's Mic Lab / Re: Neumann km54 faulty
« Last post by klaus on May 17, 2018, 12:44:44 pm »
Agree with Uwe, and let's get on with the show. It is not that complicated to troubleshoot at least the general area of a malfunction- capsule or amp.

By the way: your plate voltage at 33.5VDC is low, especially if it's the newer (cathode biased) version.

10
Klaus Heyne's Mic Lab / Re: Neumann km54 faulty
« Last post by uwe ret on May 17, 2018, 12:21:18 pm »
To confirm the capsule as your problem simply exhale gently a few times at close proximity and monitor the noise. If the humidity causes a significant increase/change in the noise you will have a defective capsule, or, if you are really lucky, just a capsule contaminated with dirt and spittle residue, which may be able to be cleaned by an experienced microphone specialist.
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