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Author Topic: Neumann U67 Reissue: Complete Tear Down and Analysis  (Read 28220 times)

uwe ret

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #105 on: April 27, 2020, 03:09:02 pm »

Suitable adapter cables - DIN (Tuchel or Binder) to XLR are available.
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klaus

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #106 on: April 27, 2020, 03:33:15 pm »

Yes, forgot to mention: you can always fabricate or purchase a pigtail that translates from one connector standard to the other.
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Klaus Heyne
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Mannix

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #107 on: April 27, 2020, 03:44:05 pm »

This morning I received a 15ft cannon-ended length of what I think is the old Belden cable. (Gray rigid, corkscrew shielding coming through jacket, with a neat old smell I haven't smelled in years.) Anyway, I hooked it up to the output of a 251 clone power supply and did several A/Bs with two different mic pres, comparing it to Mogami and Canare cable. You could certainly hear a difference. More definition in the lows and smoother highs. Level seemed the same. This was a vocal test of the same repeated musical phrase and counting down from 10. Next I will try acoustic. Quite impressed.
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klaus

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #108 on: April 27, 2020, 04:35:09 pm »

What you report and what I experienced, then wrote about at length, is yet another argument for listening over applying "objective" but theoretical considerations.

From the standpoint of cable technology, the Belden cable is inferior in a few aspects to "state-of-the-art" cables: inadequate shielding design, stiff, low strand-count conductors, other mechanical problems...nothing points to such a cable "sounding" preferable, in certain applications to highly-engineered products like the original Swiss EMT material, or its sibling, the Dörfler-made GAC7.

I have experienced a similar phenomenon with U47 cables: the original, thick, first-generation rubber cable with its four course, lamp-cord conductors and atrociously tinned, braided shield somehow sounds more resolved and musical with a U47 than whatever I sometimes need to replace it with (often, the rubber crumbles, and conductor jacket bits dry up and fall off).

I wish someone could reasonably well explain the relation between level of engineering and audible outcome in cables, especially where the audible outcome seems almost impossible, considering the low level of engineering. 
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Klaus Heyne
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Mannix

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #109 on: April 27, 2020, 08:13:06 pm »

I'm no expert, but maybe it's the quality of the copper. 
Don't know where Mogami or others get their wire from, but there are lots of Chinese copper wire manufacturers and very few US anymore.

I can relate an issue I had with Chinese steel vs. US steel. I had a 1964 Chevrolet that had a hood problem, being that it wouldn't stay up right or hold fast at its detents. The person I bought it from had installed reproduction hood hinges and springs. I called the company that he bought them from and they sent me new ones. I installed them. Same problem. I searched for NOS hinges and springs and found a set. These were GM-made US steel. I installed the first one of two. It's all it needed for the hood to obey my commands. Just one, mind you.

Long story short: the Chinese steel flexes just enough to not hold the hood. The US was solid. Same thickness, same weight (I weighed them) same exact appearance. Any copper experts here?
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Derek Samuel Reese

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #110 on: April 28, 2020, 10:21:03 am »

Suitable adapter cables - DIN (Tuchel or Binder) to XLR are available.
This sounds great, I've been searching for a suitable cable for the output stage like a Tuchel to Xlr but haven't had any luck ?
but i did find a picture of a cable that looks like it would fit, but it is advertised as for a Beyer microphone.
would you happen to have a link handy ?
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Derek Samuel Reese

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #111 on: April 28, 2020, 10:38:06 am »

This morning I received a 15ft cannon-ended length of what I think is the old Belden cable. (Gray rigid, corkscrew shielding coming through jacket, with a neat old smell I haven't smelled in years.) Anyway, I hooked it up to the output of a 251 clone power supply and did several A/Bs with two different mic pres, comparing it to Mogami and Canare cable. You could certainly hear a difference. More definition in the lows and smoother highs. Level seemed the same. This was a vocal test of the same repeated musical phrase and counting down from 10. Next I will try acoustic. Quite impressed.
You said you hooked it up to the “output” of your 251 clone power supply ?
I think Klaus was speaking of connecting the Belden cable from the microphone to the “input” stage of the power supply ?
I am asking because if you hear a significant difference on the output stage, then that tells me that both input and output cables are equally important?
Klaus any thoughts ?
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Mannix

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #112 on: April 28, 2020, 12:53:31 pm »

I bought the last one off a guy on Ebay. Sorry. Good luck.
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klaus

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #113 on: April 28, 2020, 01:18:17 pm »

You said you hooked it up to the “output” of your 251 clone power supply ?
I think Klaus was speaking of connecting the Belden cable from the microphone to the “input” stage of the power supply ?

Depends what voltage you are referring to: the power supply's INPUT receives the audio from the mic, its OUTPUT powers the mic. 
As the cable between mic and power supply serves both functions, and electrons flow in both directions, it's best to refer to that  cable as the "microphone cable", in difference to the power supply's "audio-out" cable
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Klaus Heyne
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DanDan

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #114 on: May 01, 2020, 06:57:04 pm »

Quote
So, a question-- using a mic preamp with a transformer-coupled input, is it better to aim for matched impedance with the microphone, rather than bridged impedance?

Many traffo output devices were designed with a match in mind. When a modern mismatch is in play, I have seen recommendations to strap a 600 Ohm resistor across say an 1176.

Klause, tx for a very interesting thread and for all the work that went into it.
I have two 67's. One ancient, the other the earlier reissue, in the 90's I think. The FR looks identical but I always find myself preferring the older one. Capsule tension?
Can the newer cap be detensioned?
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Dan FitzGerald  MIOA MAES
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klaus

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #115 on: May 01, 2020, 07:33:24 pm »

Any capsule in the K47/67/870/87 design family can be tension-adjusted. But I doubt very much that you have a tension problem with a 1992 K67. Those were good years, in general.

Please contact me privately if you have specific concerns you wish me to address.
I'd like to keep the forum uncontaminated from business inquires and solicitations.

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Klaus Heyne
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David Satz

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #116 on: May 02, 2020, 09:51:22 am »

DanDan, I'd just like to warn against the risk of over-generalization. Your recent message touches on two such risks that I see:

>> using a mic preamp with a transformer-coupled input, is it better to aim for matched impedance with the microphone, rather than bridged impedance?

I don't immediately see who here asked that question in that way, but anyone who tries to answer it should be a bit careful. To my mind the only valid, neutral answer is "it depends on the operating conditions that the preamp was designed for"--in other words, it depends mainly on the microphones that you're going to use. But microphones designed to be loaded by the equivalent of their own output impedance haven't been made in an extremely long time--so long that they aren't merely "vintage"; they're antique. If you're interested in breaking one of those out of a museum somewhere and trying it, then by all means get yourself an appropriate preamp for the experiment; those microphones won't sound as they were meant to do unless they are loaded as designed. But otherwise, keep away.

To look only at whether a preamp has an input transformer or not, and to assume that this must be the determining factor, is the "streetlight effect" in action. The history of studio practice in the United States, and the loss of Bell Telephone / Western Electric's early dominance over it, are more to the point. 19th-century telegraph systems are where impedance matching comes from; telephone systems were then built onto that infrastructure, which combined balanced signaling with impedance matching. But those two circuit characteristics are really two distinct items.

The only reason anyone gets interested in impedance matching in audio today is that it's been dead so long, hardly anyone alive was there when it died. So the forgetting process has become nearly complete--and those who don't know history start doing what they are proverbially doomed to do.


> The FR looks identical but I always find myself preferring the older one. Capsule tension?

If you change the capsule tension, perhaps you will like the tone better (and perhaps not), but the frequency response and impulse response of the microphone will change as well. Sensitivity, distortion, maximum sound pressure level could all be affected.

A capsule is a complex system with multiple, interdependent parameters. You can't just tweak one and have only one aspect of the system's behavior change, while all its other aspects kindly hold still.

--best regards
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afterlifestudios

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #117 on: May 02, 2020, 11:30:01 am »


Klause, tx for a very interesting thread and for all the work that went into it.
I have two 67's. One ancient, the other the earlier reissue, in the 90's I think. The FR looks identical but I always find myself preferring the older one. Capsule tension?
Can the newer cap be detensioned?

Could you swap the two head assemblies to see if your “preference” follows the amp or capsule?  Or are there physical (or electrical) differences in the 90’s reissues that prevent that?
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klaus

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #118 on: May 02, 2020, 12:58:51 pm »

You can swap without consequences.
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Klaus Heyne
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DanDan

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Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Reply #119 on: May 02, 2020, 07:11:34 pm »

Thanks Klaus, that is reassuring.

Tx David, regarding the impedance matching. I might be suffering a little cabin fever and replied in the wrong thread, but somebody did ask about matching vs bridging. 
I note some if not all of my Neuman have adjustable output impedances.
They are probably all set at 150Ω. This seems to work fine with trafoless GML preamps etc. but  I wonder should I drop to 50Ω for my V76 and V78s?
I do strap to 600Ω on the output of my 1176s.
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Dan FitzGerald  MIOA MAES
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