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 1 
 on: Today at 09:27:31 am 
Started by Joe_caithness - Last post by cook90
Cool! I liked that. Seems like it took much effort to write this topic. But it was worth it!
research papers help

 2 
 on: Yesterday at 01:12:22 am 
Started by FoxFoxFox - Last post by klaus
I am sorry to contradict, but that drawing is from January 2004, with "Circ. Diag. 04" marked on the right side. To my knowledge there is no rev. 7 out yet.

Current U87Ai (circuit #06) do no longer use the daughter board, as I have confirmed by inspecting new U87Ai over the last two years. Please check with Martin Schneider to confirm what date the transition occurred.

In addition, I will post a picture of a current mic amp layout, next time I purchase a new U87Ai.

 3 
 on: July 24, 2017, 07:11:27 pm 
Started by FoxFoxFox - Last post by uwe ret
Since 2002 (rev. 05) the FET daughter board has been used to replace the specially selected 2N3819 or equivalent. The board is still used, as evidenced in the latest schematic for rev.07:

 4 
 on: July 24, 2017, 04:58:15 pm 
Started by FoxFoxFox - Last post by klaus
The daughter board was introduced with circuit revision 04 in 2002 (ca. 8x.xxx ser. number) and discontinued with circuit revision 06, ca. 2014/15 with serial numbers in the low 120000.

To the best of my knowledge the U87A is NOT available with the 2N3819.
Starting with rev. 06 Neumann uses a discrete Fairchild 2N3819 FET in all U87Ai. That FET is also used in the high impedance stage of the recent U47fet reissue.

 5 
 on: July 24, 2017, 04:11:57 pm 
Started by FoxFoxFox - Last post by uwe ret
To the best of my knowledge the U87A is NOT available with the 2N3819. If anyone cares to compare the datasheets for the 2N3819 and the SST309 (used in the FET replacement daughter board) you will find improved noise specifications and tighter tolerances for the SST309. Then add consideration for the added optimization circuit and ask yourself why take a backward step to the previous, albeit simpler circuit?

 6 
 on: July 24, 2017, 02:43:33 pm 
Started by FoxFoxFox - Last post by Kai
... why would Neumann have dropped the daughter board?
So the current production U87 microphones are back to single 3819 FET again?
If yes, is it possible to identify those from the outside?

 7 
 on: July 24, 2017, 01:21:39 pm 
Started by FoxFoxFox - Last post by klaus
(...) Compared to the original single FET circuit the result is lower noise, slightly better dynamic range and/or lower distortion due to the automatically optimized and more stable operating point.
It was my understanding that Neumann was unable to source a high-quality discrete 3819 FET, therefore designed the "work-around" daughter board. Once they found a quality 2N3819 (Fairchild), they dropped the daughter board again.

But assuming your contention is correct that the mics with the daughter board have better specs, I am sure you already anticipated the next question: why would Neumann have dropped the daughter board?

 8 
 on: July 24, 2017, 12:26:08 pm 
Started by FoxFoxFox - Last post by Jim Williams
It's not the SOIC semiconductors, it's the SOIC passives. You do not want to run a $3000+ microphone into a mono ceramic coupling capacitor in place of a polystyrene film.

If one wants to investigate why those are a poor choice, read up on the Marsh-Jung papers in the AES journals.

 9 
 on: July 23, 2017, 11:25:39 pm 
Started by FoxFoxFox - Last post by uwe ret
If it isn't broke, don't try to 'fix' it! Contrary to what may be expressed here and elsewhere, the single FET substitution with the daughter board is actually a real improvement. There is still effectively only one active FET (selected for minimal noise) in the signal path, the other seemingly cascaded one in conjunction with a dual PNP-pair automatically optimizes the operating point, and the single NPN forms the load resistance for the FET. Compared to the original sindle FET circuit the result is lower noise, slightly better dynamic range and/or lower distortion due to the automatically optimized and more stable operating point. Going out on a limb, I would argue to replace to replace any (defective) FET in the older U87A models with this daughter board!

 10 
 on: July 22, 2017, 09:20:11 am 
Started by FoxFoxFox - Last post by FoxFoxFox
Thats what I thought too... All i need is the mod, and I was quoted 300-500$ by Tom O. That doesn't sound right. Anymore recommendations in the area would be great! thanks

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