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Author Topic: U87i & U87ai....Differences?  (Read 15664 times)

Working Musician

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U87i & U87ai....Differences?
« on: May 21, 2004, 03:15:13 pm »

I was able to purchase a u87i in great condition which after checking the seriel number, found out was made in 1974. Was curious to know what the major differences were between the "i" and the "ai" which took its place in 1987.

The battery for internal power and its meter in the "i" series was the only real physical difference I noticed. I heard through other sources that the "ai" had a raised output level.

Any information appreciated.


Mark Baker
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Regards
MJB

Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #1 on: May 22, 2004, 03:56:33 pm »

I am sure David Satz could execute a precise, all encompassing narrative of the differences.
In the meantime I try a Klutz version:

The central difference between the U87 and its successor U87A was the introduction of a DC-DC converter in the new model (the 'i'-suffix identifies an XLR connector, which all U87A and most U87 have anyway.)

What is a DC-converter?  It is a circuitry ,situated in the space where the battery compartment of the old U87 was, that increases the phantom power's available 48VDC to 60 VDC, and thereby polarizes the capsule voltage with 12 more volts than in the U87.
The extra volts available at the capsule increase the output of the mic by about 10dB. The side effect of the output improvement is a slight reduction in headroom (distortion from very loud sound sources) by 5-6 dB.

All other audio and EQ parameters of the two mics remain the same.

One other advantage of the DC converter is that now the U67 capsules and the (identically constructed) U87A capsules, known as K870, are interchangeable.  

The old U87 capsule required an isolation washer between the capsule halves, to generate three patterns out of 48V, which made the U67 and U87 capsules not interchangeable.

Kind regards,
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Klaus Heyne
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Henrik Vogel

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Re: U87i & U87ai....Differences?
« Reply #2 on: May 23, 2004, 08:29:51 am »

Klaus Heyne wrote on Sat, 22 May 2004 21:56


All other audio and EQ parameters of the two mics remain the same.



They do? I have never been in the position to compare a U87 and a U87ai side by side, but what I hear from others is that the ai is brighter which many people seem to dislike. Are you saying this isn't so?

Best,
Henrik Vogel
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David Bock

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Re: U87i & U87ai....Differences?
« Reply #3 on: May 23, 2004, 02:47:17 pm »

It's true the amount of HF rolloff is reduced in the more recent U87.
regards,
DB

Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #4 on: May 24, 2004, 03:30:15 pm »

The Neumann frequency plots of U87 and U87A show a difference of high frequency peak in the 7-10k region of less than 1dB between the two models (facilitated by a change of the HF Eq cap from 220pf to 160pf.)

I am not sure whether less than one dB difference qualifies as "the same" or "brighter".  "Harder" may be a better term, caused by the significantly "stiffer" polarization voltage.

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Klaus Heyne
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Loco

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Re: U87i & U87ai....Differences?
« Reply #5 on: May 24, 2004, 05:11:36 pm »

Henrik Vogel wrote on Sun, 23 May 2004 08:29

I have never been in the position to compare a U87 and a U87ai side by side, but what I hear from others is that the ai is brighter which many people seem to dislike. Are you saying this isn't so?


As the Ai is louder, people may say it is "clearer" or bright. It could be confusing. However, as it is easy to overload internally, it is easy to overload preamps as well with it.

And they seem to load differently the preamp or something. You cannot make one sound like the other simply by changing the gain on your Pre. Your vocals will get a different edge between both models, none of them my favorite flavor of U87. My choice is the U87Ki.
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Carlos "El Loco" Bedoya

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David Satz

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Re: U87i & U87ai....Differences?
« Reply #6 on: May 24, 2004, 06:29:37 pm »

Hello, loco--

Pray tell, what is a U 87Ki?  Is that a U 87i with potassium added?

(or by chance might it be a "highly Klausified" U 87i ?)

--best regards
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Loco

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Re: U87i & U87ai....Differences?
« Reply #7 on: May 25, 2004, 11:33:34 am »

Is potassium what Klaus adds to the U87?

Klausified, indeed. The desert-island Mic. I have yet to find a vocalist that won't suits this beauty.
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Carlos "El Loco" Bedoya

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Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #8 on: December 10, 2010, 06:52:49 pm »

Update:
This thread was started in 2004, and since then, in addition to surface finish changes, two additional things have been incorporated in the U87A:

1. The discrete FET has been replaced with a sub-circuit board containing several surface mounted solid state components: Neumann could not find a decently quiet and reliable single J-FET anymore on the market, and substituted it with a new circuit.

2. The K870/67 capsule performance has changed. There are several threads where this is discussed (someone with a bit more time than me may want to help and link these threads.)
To summarise: The low end is tighter now, most likely due to higher tension of the two diaphragms, and most likely to reign in manufacturing tolerances/reduce rejects/save money.
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Klaus Heyne
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kats

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Re: U87i & U87ai....Differences?
« Reply #9 on: December 11, 2010, 12:06:15 am »

Klaus, when were these new changes ushered in?
Thank you.
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Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #10 on: December 11, 2010, 02:25:00 am »

Around serial number 85000 the new sub-board was introduced in the U87Ai. This would have been ca. 2005/6.

Around the same time, or maybe a year later, the K870 capsules started to sound noticeably drier in the bass (not ALL capsules, but many.)
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Klaus Heyne
German Masterworks
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Donn Halliburton

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Re: U87i & U87ai....Differences?
« Reply #11 on: December 12, 2010, 01:35:54 am »

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

Donn
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radiovinheta

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Re: U87i & U87ai....Differences?
« Reply #12 on: December 13, 2010, 08:47:29 am »

"Several surface mounted solid state components" on "newest" u87Ai?... OH MY GOD!!!!!  Mad  Mad  Mad
That's why i DON'T LIKE any new NeumannHeiser mic.

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MagnetoSound

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Re: U87i & U87ai....Differences?
« Reply #13 on: December 13, 2010, 09:32:46 am »

Klaus Heyne wrote on Fri, 10 December 2010 23:52

Neumann could not find a decently quiet and reliable single J-FET anymore on the market




Really? What happened?


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Klaus Heyne

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Re: U87i & U87ai....Differences?
« Reply #14 on: December 13, 2010, 01:41:30 pm »

If you remember, demand for high-quality discrete FETs, especially of the Texas Instrument-pioneered 2N3819 variety, dried up in the 1990s. Who needed them anymore? Everything went to SMT technology, so discrete solid state components were no longer in demand, and high-quality samples of these discretes were no longer manufactured. With other words, except for some off-shore junk, that model FET was dead.

This has now changed. Fairchild has just reintroduced their version of the 2N3819. I am about to test them (Andreas Grosser sent me some), and have high hopes. This does not mean that Neumann will re-tool. We will have to see. The extra step of biasing each FET individually (as it was done with discrete FETs) may be too much of a cost factor for Sennheiser to green-light it.
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Klaus Heyne
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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
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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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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
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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
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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
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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
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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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