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Author Topic: Neumann KM76 and KM86  (Read 10465 times)

ryan streber

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Neumann KM76 and KM86
« on: April 27, 2004, 09:56:06 PM »

I'm having a hard time finding info about the KM76, and I'm wondering if anyone can remark on this mic, differences between it and the 86 (pros and cons), etc.  
Thanks!
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Oliver Archut

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Re: Neumann KM76 and KM86
« Reply #1 on: April 27, 2004, 11:33:09 PM »

The Neumann 7X series is the wire feed (a-b powering) version developed by the IRT, their opinion was that +48V is a sub-standard powering. Some mics like the U77 is the A-B version of the U87 but some mics have minor differences to their 80s series counterparts. Aside higher headroom/better dynamic range, those mics are great for outdoor recording due to the fact that they are running on +12V, so every car battery is a good power source.
Before TLM mics the 7x series was the first transformer less mic and works via a split load, quite nice in my view the best transistor mics ever made...
Sadly so many are converted to 48V...

Neumann doesn't have to much info on their web-page if you need the IRT data comperission 48V A-B let me know it is in german...

Regards,

Oliver
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Oliver Archut
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We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

David Satz

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Re: Neumann KM76 and KM86
« Reply #2 on: April 27, 2004, 11:43:02 PM »

The KM 76 was the parallel-powered predecessor of the phantom-powered KM 86. It used the same capsule head and generally had generally the same specifications and sound quality.

The big disadvantage of the KM 76 is the special power supply which it requires. And if you accidentally plug a dynamic or ribbon microphone into that supply, the damage could be expensive; parallel powering isn't compatible with dynamic microphones!

This microphone is a nice variation on the KM 84 sound in the cardioid setting, but its figure-8 setting is a disappointment. It has rather nasty off-axis peaks at high frequencies. This is visible in the published polar diagrams and easily audible if you record, say, an energetic soprano voice in a live room.

--best regards
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David Satz

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Re: Neumann KM76 and KM86
« Reply #3 on: April 27, 2004, 11:51:57 PM »

Hello, Oliver--

Sorry to quibble, but Neumann's published specifications for the KM 86 actually give a slightly higher maximum SPL for the KM 86 than for the KM 76 (121 dB SPL vs. 120), and a slightly lower equivalent noise level (26 dB SPL unweighted vs. 27).

So it would seem that the dynamic range of the KM 86 is supposed to be about 2 dB greater than that of the KM 76.  That's not very much, but it isn't the other way around.

--best regards
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ryan streber

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Re: Neumann KM76 and KM86
« Reply #4 on: April 28, 2004, 12:38:53 AM »

Thanks for the replies - extremely helpful and informative!  Perhaps I'm misundertanding something, but I'm unclear about the power supply.  Was the original system configured with an independant powersupply or was it simply an a/b box that converted 48v (from an external source) to 12v for the mic?  
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David Satz

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Re: Neumann KM76 and KM86
« Reply #5 on: April 28, 2004, 04:02:44 AM »

Ryan, yes, there were (and still are) special 9 - 12 Volt parallel power supplies. One of the most common uses of parallel-powered microphones for many years was location sound for film, since Nagra portable recorders implemented this powering system long before they had preamps with phantom powering. Sennheiser parallel-powered shotgun microphones and Nagra recorders were and still are a common combination. Schoeps has made parallel-powered microphones in both the CMT and the "Colette" series--the CMC 441 is still a standard for film and video recording.

The system is not well-suited to studio use, however, since it is in no way compatible with any other type of microphone and can damage many kinds of microphone severely.

It's interesting to note that Neumann's T-powered microphones had transformerless output circuits.  However, it doesn't seem to have helped them much, since the maximum undistorted output level of the KM 76 is certainly no higher, and is actually a tiny bit lower (SPL-wise), than that of the KM 86.

--best regards
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ryan streber

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Re: Neumann KM76 and KM86
« Reply #6 on: April 28, 2004, 08:16:56 AM »

Thanks David so much for your help, and sorry for my misunderstanding of the ps issue!  I'm thinkning of picking up a used KM76 that has the "little box" (converts from phantom to t-power) but I'm feeling woefully ignorant of what may or may not have been done to the thing in terms of mods or conversions.  It does sound like an interesting mic, though.
Thanks again!
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Oliver Archut

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Re: Neumann KM76 and KM86
« Reply #7 on: April 28, 2004, 11:32:41 AM »

Hello David,

hey you are right, my finger slipped in the wrong place while looking. Thanks for pointing it out...

Best regards,

Oliver

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Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

David Satz

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Re: Neumann KM76 and KM86
« Reply #8 on: April 28, 2004, 11:45:56 AM »

Oliver, I'm relieved to find out that we're not in any disagreement. Thanks for your note.
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analog Tom

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Re: Neumann KM76 and KM86
« Reply #9 on: May 05, 2004, 01:12:55 AM »

Ryan,  

If you are looking at one of these mics, be aware that the pattern selector switch, just under the head, is very delicate, and that Neumann no longer supports it (if it's broken, there are no replacement parts).  

My understanding is that there was only a tiny number (around 50?) of the 76s made before the 86 came out.  

The PSC "universal" supply (also offered with the Sennheiser label) is ideal for T powered mics like the 76.  It runs on a 9v battery, and can be used for both T power (76) and phantom power (86) mics (and others by Sennheiser, Schoeps, etc.)  Very small, very convenient, very easy to walk off on a busy location.

Cordially,
Tom
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David Satz

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Re: Neumann KM76 and KM86
« Reply #10 on: May 18, 2004, 07:58:04 PM »

Now that I've learned how to use the forum's graphics upload software, maybe I can illustrate the problem that I was referring to in the KM 86's off-axis high frequency response.  Here is a clip (slightly rearranged to save space) from the set of response graphs which Neumann published for the FET 80 series in Oct. 1973:

index.php/fa/766/0/

Everything's copacetic up through 4 kHz, as shown on the right half of the polar graph.  But the response in the two octaves above that, as shown on the left side, has large response variations which are highly "angle-specific," starting from about 30 degrees on around to the nulls at the sides.

If you plot these variations onto the on-axis response shown, you'll see that at 8 kHz, for example, the microphone has a 6 or 7 dB response elevation at 45 degrees off-axis.  And that's exactly the part of the mike which you would aim at the center of the sound source in a Blumlein setup!  It's also the part of the mike that would be aimed at center left or center right in an M/S configuration.

I made the mistake of trying to record a very lively soprano voice with a pair of these microphones in a bright, live room once; I won't make that particular mistake soon again, especially given the talent I have for inventing fresh, new kinds of mistakes.

--best regards
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Klaus Heyne

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Re: Neumann KM76 and KM86
« Reply #11 on: May 19, 2004, 02:38:55 AM »

I would not at all be surprised if the off-axis weirdness of this mic was emphasized, if not wholly created, by the unusual mesh-layering in front of the two capsules inside the dome: you are dealing with not one, but four(!) layers of super-fine, fine, in-between, and course wire mesh in front of each capsule.

The reflections, particularly from the super-fine mesh which is right in front of the capsule in a completely parallel arrangement with the diaphragm, could be the cause of all this. The wave lengths are about right, if I look at the polar diagram - 8k and 12.5k - to account for the off-axis artifacts.

Kind regards,
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Klaus Heyne
German Masterworks
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David Satz

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Re: Neumann KM76 and KM86
« Reply #12 on: July 31, 2004, 03:15:18 PM »

Klaus, have you ever tested a KM 86 with its wire grille removed? If the off-axis weirdness were caused by the wire mesh, why is hardly any such weirdness apparent in the cardioid setting of the microphone? The sound arriving at both sides of the front diaphragm still has to go through the screened capsule head.
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Klaus Heyne

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Re: Neumann KM76 and KM86
« Reply #13 on: August 02, 2004, 01:51:05 AM »

David Satz wrote on Sat, 31 July 2004 12:15

Klaus,
Have you ever tested a KM 86 with its wire grille removed? If the off-axis weirdness were caused by the wire mesh, why is hardly any such weirdness apparent in the cardioid setting of the microphone?


David,
You cannot remove the outer grille from a KM86 because of stray hum. You would have to test the mic inside a Faraday cage that would need to have room for the listener and the mic and the sound source.

But you can, and this is part of my KM86 modification, remove the tightly woven mesh in front of the KK84-type capsules in that mic. This mesh is completely useless and without any function in the KM86. This is not a do-it yourself job, as the capacitance of the capsule systems has to be recalibrated after removal of the mesh and reinstallation of the diaphragm plate!

Please do not remove the mesh from a KM84 capsule when used in a KM84 mic! The mesh is very much needed to protect the capsule's diaphragm from particles and air movement;

As mentioned earlier in another thread regarding some of the shortcomings of the KM86, the removal of this mesh which forms a sound barrier, opens the mic's sound up considerably.

Regarding the off axis weirdness (which in this mic I find just as phasey and weird in cardioid as in all other patterns): You are of course right that a screen at close proximity to, and parallel with, the diaphragm would not have an effect on the off-axis performance, as measured with a sine wave sweep.

What the four screens in the KM86 introduce, and which a lay person could describe as a "phasing" effect , is actually generated by cumulative comb filtering and standing waves: the comb filtering comes from the wire meshes of varying thickness which are frequency discriminating; the standing waves come from the circular grille surrounding the capsule heads and the two parallel surfaces of tight-screen KK84 mesh and diaphragm.)

The phasing is not discriminating per se to angle of arrival, but is maybe more noticeable off axis, when certain frequencies are more or less prominent, through resonance or filtering, as described above.

Long story short: Even without any additional electronic improvements, the KM86 mic is a more useful, lively, musical tool once the innermost screens from the two capsule heads have been removed.

Kind regards,
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Bob Schwenkler

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Re: Neumann KM76 and KM86
« Reply #14 on: March 03, 2006, 01:28:08 PM »

Hi,

I was searching around for certain bits of information on the KM86 and came across this post, which suggests removal of the innermost mesh screen. Klaus, in parentheses you state that this is not a DIY job, but I am unsure if you are referring only to the KM84 when you make this statement. Does this warning apply to both the KM84 and the KM86?
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