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Author Topic: U87i & U87ai....Differences?  (Read 16140 times)

David Bock

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Re: U87i & U87ai....Differences?
« Reply #15 on: December 13, 2010, 06:35:05 pm »

(on further differences between the U87 and U87A):
that DC-DC converter for polarization volts also assures that the 60V polarization doesn't vary with P48 phantom voltage the same way the old system did (due to different and varying loads on the phantom supply)

Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #16 on: December 13, 2010, 11:45:26 pm »

Donn Halliburton wrote on Sat, 11 December 2010 22:35

Would it be possible to see a picture of the difference between circuit boards, like an A/B pre/post sub circuit board?

I only have a picture of the current configuration, with sub-chip (mic serial number 952xx.)

The older version U87A had one discrete FET right underneath where the sub-chip is now mounted, and  the original slots for the drain and source resistors, as well as the source cap, are still there but empty.

index.php/fa/15988/0/
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Klaus Heyne
German Masterworks
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J.J. Blair

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Re: U87i & U87ai....Differences?
« Reply #17 on: December 14, 2010, 12:51:12 am »

SMD daughter card.  Kinky!
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studio info

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David Bock

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Re: U87i & U87ai....Differences?
« Reply #18 on: December 14, 2010, 01:17:41 am »

so now, 3 or four transistors in place of one.

Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #19 on: December 14, 2010, 02:22:40 am »

The original, discrete FET set-up is easily restored by a good technician or conscientious lay person.
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com

radiovinheta

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Re: U87i & U87ai....Differences?
« Reply #20 on: December 14, 2010, 10:09:24 am »

What about sonic differences between U87A "discrete" and U87A "SMD"?
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MI

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Re: U87i & U87ai....Differences?
« Reply #21 on: December 14, 2010, 10:17:38 am »

Klaus Heyne wrote on Tue, 14 December 2010 02:22

The original, discrete FET set-up is easily restored by a good technician or conscientious lay person.


Good to know.

Otherwise the 90's ai will soon be "Vintage" on ebay.... Confused

Mario
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Jim Williams

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Re: U87i & U87ai....Differences?
« Reply #22 on: December 14, 2010, 11:44:46 am »

I have one of these newer models in now, it has a problem with cut out as the jfet is not biased properly. That daughter pcb is a real mess. Besides the fact it's completely coated in non conformal dope, the surface mount ceramic caps and metal oxide resistors sound like crap and can't be removed for adjustment.

Given the choice of ordering an expensive replacement made out of the same crap, I elected to remove it completely. The main audio PCB is still the same, I just reinstalled high quality through hole components and now I can tune the jfet, which is several db less noise than whatever Sennheiser selected.

As I have done several mods to these new daughter pcb versions of 87's, I will no longer deal with that, that daughter pcb will be removed and the proven quality through hole parts will be used. The other benefit is I can now lower the self noise of the mic to around 6 db as I'm no longer stuck using Sennheiser's mystery jfet.
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Jim Williams
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zebra50

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Re: U87i & U87ai....Differences?
« Reply #23 on: December 14, 2010, 12:36:54 pm »

Here's an older U87ai, with discrete FET.

http://www.xaudia.com/omnip/Mics/Neumann/U87a_2.jpg

Stewart
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Stewart Tavener
Xaudia - studio, ribbon mic repairs
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Sauly

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Re: U87i & U87ai....Differences?
« Reply #24 on: December 19, 2010, 12:19:30 am »

So how closely can a current production U87ai be modded to sound/be constructed like an original U87?
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Jim Williams

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Re: U87i & U87ai....Differences?
« Reply #25 on: December 19, 2010, 12:35:43 pm »

Depends on what you call close. Yes, you can remove the rear oscillator pcb, then you need to "arrange" the phantom to polarize the capsule. That requires mucho rework as the entire polarization design is different.

So, yes you can rework the electronics to resemble the earlier designs. What you can't do is recreate the single back plate design of the older capsule.
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Jim Williams
Audio Upgrades

Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #26 on: December 19, 2010, 01:30:46 pm »

Jim Williams wrote on Sun, 19 December 2010 09:35

(...) What you can't do is recreate the single back plate design of the older capsule.


The older U87 capsule was never a single backplate design. Neither is the new one. The acoustic design of the current capsule is unchanged from even the earliest version of the capsule (1960.)  All that has changed is the spacer material dividing the two back plates.

Can you explain what you mean?


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Klaus Heyne
German Masterworks
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David Bock

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Re: U87i & U87ai....Differences?
« Reply #27 on: December 19, 2010, 02:00:18 pm »

Right, the original 87 used 48v for polarization, had two backplates insulated from each other and switched various combinations of Vp to backplates & membranes to achieve patterns. The new one with the backplates electrically connected uses variation of rear membrane voltage to achieve pattern control. Always dual backplate design.
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