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Author Topic: U87Ai Sub-Board: How Bad Is It?  (Read 4294 times)

Offline FoxFoxFox

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U87Ai Sub-Board: How Bad Is It?
« on: July 18, 2017, 03:54:12 am »
Okay I see you do not like this circuit board  ;D (Sub board, also called "daughter board, as used in U87Ai with circuit # 04 and #05. K.H.) the mic sounds really full, fuller than I expected on the other hand! Anyway to get rid of that daughterboard and make it as stock as the ones without the daughterboard... ?
« Last Edit: July 25, 2017, 03:00:32 pm by klaus »

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #1 on: July 18, 2017, 11:27:24 am »
In circuit revision # 4 and #5, the 'daughter board' replaced the previous discrete FET circuitry on U87Ai circuits.
It can easily be removed, and a few missing passive components and a new 2N3819 FET (properly biased) installed. Once the FET is properly biased, you would be back to the simpler, better-sounding circuitries # 2 and #6.
« Last Edit: July 25, 2017, 03:00:52 pm by klaus »
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline FoxFoxFox

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #2 on: July 18, 2017, 11:41:17 am »
Okay which one is mine then because I thought the daughter board was the floating tray, because mine is circuit 5, and it def has that "floating tray" on top of the regular board
« Last Edit: July 21, 2017, 09:31:06 am by FoxFoxFox »

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #3 on: July 18, 2017, 12:12:00 pm »
Yours has the daughter board. I forgot to include circuit #5 as the other revision that used the daughter board (previous post now corrected).
« Last Edit: July 18, 2017, 06:12:59 pm by klaus »
Klaus Heyne
German Masterworks®
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Offline FoxFoxFox

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #4 on: July 18, 2017, 07:53:05 pm »
Thanks Klaus!! I want to do the mod to get it back to #2 and #6, who do you recommend in NYC? also how much do you think this job typically cost

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #5 on: July 18, 2017, 11:53:16 pm »
You can try Tom Onofrio in Connecticut. He used to work at Neumann/Sennheiser in Old Lyme.
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline soapfoot

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #6 on: July 19, 2017, 08:47:00 am »
Second the recommendation for Tom O.

Offline FoxFoxFox

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #7 on: July 19, 2017, 10:43:09 pm »
i want to, but its quite expensive
« Last Edit: July 19, 2017, 10:45:31 pm by FoxFoxFox »

Offline FoxFoxFox

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #8 on: July 21, 2017, 09:31:23 am »
does 300-500$ sound a little high for this job?

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #9 on: July 21, 2017, 11:30:03 am »
I am questioning the wide range of the estimate. Unless there are other issues your mic has*, FET conversion should be a well defined, straight job.

*For that reason I avoid giving estimates before I see a mic. But there are rare cases, where the scope of work is clearly defined, because other problems the mic may have can be safely excluded (capsule cleaning, cable manufacturing, etc.)
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline FoxFoxFox

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #10 on: July 21, 2017, 11:46:08 am »
Strange, respectfully this is a quote from Tom O. He also doesn't do it either but that was the range he gave me. The mic is rock solid, the signal to noise ratio sounds astonishingly good
« Last Edit: July 22, 2017, 02:01:10 am by klaus »

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #11 on: July 22, 2017, 02:04:30 am »
He also doesn't do it either but that was the range he gave me.

Maybe I misunderstand this sentence, but shouldn't an estimate be somehow connected to its service provider?
« Last Edit: July 22, 2017, 09:51:17 pm by klaus »
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline FoxFoxFox

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #12 on: July 22, 2017, 09:20:11 am »
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

Offline uwe ret

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #13 on: July 23, 2017, 11:25:39 pm »
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!

Offline Jim Williams

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #14 on: July 24, 2017, 12:26:08 pm »
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.

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #15 on: July 24, 2017, 01:21:39 pm »
(...) 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?
« Last Edit: July 24, 2017, 04:41:39 pm by klaus »
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline Kai

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #16 on: July 24, 2017, 02:43:33 pm »
... 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?
« Last Edit: July 24, 2017, 04:43:50 pm by klaus »

Offline uwe ret

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #17 on: July 24, 2017, 04:11:57 pm »
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?

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #18 on: July 24, 2017, 04:58:15 pm »
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.
« Last Edit: July 24, 2017, 05:13:31 pm by klaus »
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline uwe ret

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #19 on: July 24, 2017, 07:11:27 pm »
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:

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #20 on: July 25, 2017, 01:12:22 am »
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.
« Last Edit: July 25, 2017, 03:07:11 pm by klaus »
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline uwe ret

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #21 on: July 27, 2017, 04:20:31 pm »
The latest schematic I have available is still for circuit diagram 04 (with the daughter board) revision 07 from January 14, 2004. To the best of my knowledge, this still does reflect the current production. Please see the ID at the lower right corner of the schematic diagram.
« Last Edit: July 27, 2017, 11:22:52 pm by uwe ret »

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #22 on: July 28, 2017, 01:32:41 am »
See arrows, and get confirmation from Berlin. I'll post a photo as soon as the next 06 arrives here. Worked on about a dozen so far.
« Last Edit: July 28, 2017, 01:34:37 am by klaus »
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline uwe ret

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #23 on: August 29, 2017, 04:25:24 pm »
To end the apparent confusion over this subject, I did contact Neumann's engineering department in Berlin, and received the following clarification about the various versions of U 87A circuits:

Circuit Diagrams:
02:         Standard-U87A Neumann (FET: 2SK10x selected)
03:         DC/DC-converter board without those components only required for U89 (from ~1995)
04:         with additional PCB 4 in place of discontinued FET (from 2002 to 08/2013)
05:         2 values of components on DC/DC-converter board changed (2011)
06:         return to single FET in place of daughter board PCB 4; same as Circ.Diag.03, plus changes from 05. (since 08/2013)

My apologies to Klaus for the confusion originating from the various definitions between Circuit Diagram # and release #.

« Last Edit: August 30, 2017, 08:57:13 pm by uwe ret »

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #24 on: August 30, 2017, 01:41:06 am »
...and, as promised, here is a photo of the current edition U87Ai (circuit #06) which shows the re-introduced discrete FET on the lower right, below the silver attachment screw.
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Offline Jim Williams

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #25 on: August 30, 2017, 12:03:20 pm »
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?

Besides the fet and transistors, there are also low quality surface mount passives used. The mono ceramic coupling caps are especially troublesome, the sonics are awful compared to a quality polystyrene cap. A better jfet will not benefit from using a ceramic signal capacitor.

"Two steps forward and one step back"  ~ Johnny Winter

Offline klaus

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Re: U87Ai Sub-Board: How Bad Is It?
« Reply #26 on: August 30, 2017, 02:49:36 pm »
Since discontinuing Tantalums (mid 1980s), Neumann uses polarized electrolytic coupling capacitors, not ceramics.

So if you want to keep the mic stock, you can keep the coupling cap but you may want to throw out the daughter board of versions #03 though #05 and replace with discrete FET, 47kΩ drain resistor, source cap and resistor (which needs to be biased) and add a 1 gig Ω shut at the FET gate.

All this is fairly easy to do (at least for a mic tech).
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com