R/E/P > Klaus Heyne's Mic Lab

Neumann U67 Reissue: Complete Tear Down and Analysis

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Iím curious about 50ohm setting on these mics for v76 as well.  But as far as line level impedance bridging/matching goes, it really matters what kind load youíre output transformer expects, and what kind of load the input of the next piece of gear presents.
Instead of strapping loading resistors on the outputs of 1176ís and other outboard, I just put some on the patch bay. That way you can easily patch it independing on the signal chain are currently using.  Sometimes your 1176 output will already be seeing a 600ohm load (patched to tape machine for instance), and sometimes it will be seeing 10k ohm (a/d converters).  You donít want a 600ohm termination resistor as well as a 600 ohm input of the next device.  So having flexibility is key, which is why I put some loading resistors on the patch bay, not on the unit.

(Sorry if this thread is drifting too far, Klaus.)

David Satz:
The 150-Ohm setting should be avoided in my opinion. It was meant to work around two defects of older preamps and mixers, but at a definite cost. Meanwhile those defects are far less prevalent today than they were in the late 1950s: [1] input overload (because the particular preamps or mixer inputs had been designed for ribbon and other dynamic microphones) and [2] input impedance below the 1 kHz minimum.

If either of those problems exists in a given case, it is far better to place a resistive pad directly at the input of the equipment that has the problem, rather than to hobble a perfectly good microphone for the sake of equipment that's not up to the demands of modern recording. If you pad the signal "after the cable" rather than "before" it, the microphone signals in the cable will be 6 to 10 dB higher in level depending on what comparison we're making exactly. That's a big advantage when RF interference or hum are a possible concern, e.g. for the type of live concert recording that I do, where there are never any retakes for the recording engineer's sake.

If you expect to use preamps with input transformers, especially if they have a large voltage step-up factor, the 200-Ohm setting may be preferable--but again, we are catering to design limitations here, because in the design of some such preamps, an assumption was made that the microphone's driving impedance would always be in the 150-200 Ohm range, and no allowance was made for a driving impedance as low as 50 Ohms. That's unfortunate in hindsight, but there are some otherwise very good preamps that follow it, unfortunately. They may deviate audibly from flat high-frequency response, and from clean impulse response, if driven by a source impedance much lower than about 150 Ohms. Sometimes this misbehavior can be cured with a benign modification of the preamp's input circuit, but that solution isn't always available.

Since my preamps don't have these restrictions, and are quiet at the gain levels I normally use, I prefer the 50-Ohm setting for my few remaining microphones that have output transformers. It has less chance of clipping the input of any preamp, and it protects the microphone's output stage better from the vagaries of cables--especially long ones which I occasionally have to work with, and/or cables with high capacitance.

--best regards

Derek Samuel Reese:
Cables do have a sound.
I tested three different cables for my U67.
I first started by listening to each cable over the course of a week by singing and talking.
Then i began recording my results so I can compare them.
This wasnít scientific i matched three different vocal takes with three different cables and matched the levels the best i could.
Repeating the same few phrases.

Microphone details-
I have a 1963 Neumann U67 with a 1978 K67 capsule which Klaus brought back to life, along with a vintage 1963 NU 67 psu that has been checked by a tech and given a clean bill of health.
I am using a 1968 Telefunken EF806s tube.
My S2 wire on my u67 is not connected.
The u67 was flat (HPF and pad switch Not engaged)

I used the internal mic preamp on an Apogee element 24 interface .
Recorded in Logic X at 24 bit 96 kHz.

Here are the results I heard-
1-Gotham GAC 7 was what came with my u67, rich low frequencies slightly congested midís and not enough high frequency presence, a dark sounding cable.

2-1992 reissue also had a rich low end and a nice mid frequency but also lacked in the upper frequencies but i also heard less dimension or width in this cable when compared to the belden and GAC 7

3-Belden was exactly everything Klaus said it was, a match made in heaven.
The low end was tight thick and round and the mid frequencies really had a beauty to them zero congestion,
while the high end frequencies were so silky without being overbearing and no sibilance at all.
Absolutely refreshing.
So I will be selling the GAC 7 and the 1992 reissue cables and most likely purchase another Belden for backup.
Thank you so very much Klaus, because of you I went ahead and bought the Belden and the reissue cable to test and thereís no turning back now.
It was worth my time and money.
Sure you can use eq to get whatever results you want, but for me i wanted the source to be as good as i could possible get it before cutting and boosting.
Ps- the only cable I couldnít get my hands on was the EMT cable, so I have no idea what that one sounds like.

How do you get dimension and width from a mono source? I find your conclusions extremely unscientific and unlikely.

Derek Samuel Reese:
When comparing all three cables, the reissue did not have the same width as the GAC 7 or Belden.
You can hear width on a mono source,
It doesnít have to be stereo in order to hear how narrow something sounds.
This was my opinion after a week of evaluation, the reissue was the only cable that sounded thinner than the rest.

I mentioned that my test wasnít scientific, but if you were here listening you would agree.
Iím also not out to try and convince anyone. I am simply reporting my findings and Iím very happy with the results and what I chose :-)
I was going to upload the audio tracks I did but your allowed Only 512kb so I would have to reduce the size which in turn affect quality so whatís the point really.


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