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Author Topic: Neumann U48  (Read 40819 times)

piedpiper

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Re: Neumann U48
« Reply #30 on: December 06, 2009, 01:40:21 AM »

Are you interested in capturing, as accurately as possible in a new mic, the sound of the original or is this not a priority?

There are a number of contestants in the U47 clone race. I have only compared two of these, and only in an on-line shoot out. These two were the Wunder CM-7 and the BeezNeez T-1 limited edition from Australia.

I preferred the BeezNeez, the Wunder being surprisingly thin and edgy in comparison. The BeezNeez is also one of the least expensive of the serious contenders, probably due to being sold direct only. The build quality seems to be anything but cheap. IMHO, on-line shoot outs are not be taken as profoundly conclusive but they can at least point at contenders for a short list to audition or consider.
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Tim Britton

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J.J. Blair

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Re: Neumann U48
« Reply #31 on: December 06, 2009, 03:59:31 PM »

I am skeptical of online shootouts, unless I thoroughly trust the person who made it to be as diligent as I am.  If that shootout is posted at (another well-known forum), I'm especially skeptical.

My personal, first hand experience comparing the CM7 to a real Neumann U47 was very favorable, and I have no problem recommending the CM7 to anybody who does not want to spend the going price for a U47, but wants that flavor.  

The only thing that really sounds like a U47 is a U47, but the CM7 does an excellent job getting you in the ballpark.
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studio info

They say the heart of Rock & Roll is still beating, which is amazing if you consider all the blow it's done over the years.

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Klaus Heyne

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Re: Neumann U48
« Reply #32 on: December 06, 2009, 04:46:36 PM »

How big is the ballpark?
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Klaus Heyne
German Masterworks
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piedpiper

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Re: Neumann U48
« Reply #33 on: December 06, 2009, 08:13:33 PM »

Perhaps the "contenders" are in the ball park, and the real U47 hits it over the fence.

Re: the "shoot out" seemed to have been done pretty carefully but still...

My point, as I said, was not to draw undue conclusions, but to include the BeezNeez T-1 as a very interesting mic to consider. I have heard great things about the CM7, as well as having heard it in person, although not in comparison until this shoot out, but in this case, an older U87 and the BeezNeez T-1 easily bested it. In this shoot out, no real U47 was included, nor any of the other clones per se, such as the Flea, Wagner, etc..
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Tim Britton

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Greg Norman

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Re: Neumann U48 help?
« Reply #34 on: January 14, 2010, 06:37:08 PM »

We have a problem with our U48 that maybe be familiar to someone here..
Recently the output of our mic dropped considerably in level, and there is almost no low frequency response.  It sounds similar to when a wire breaks off pin 2 or 3 on a transformer balanced mic (low output, noisy, tinny sounding).
Some observations-
It has a VF 14 tube S/N 063
With the mic connected to the PSU, on for 20 minutes, I can measure-
105.5 V coming in,
Filament voltage seems correct at 36v and 1.1v (cathode side)
21.8v at the plate/g3/g2 (which I understand should be 34v).
At the junction of R7, R8, and C5, I measure 86v
With the mic off, and disconnected from PSU-
Using a BK Precision LCR meter, I measured an impedance of 1.6kΩ across the output (transformer strapped for "200Ω").  DC resistance there is about 160Ω.
 
The transformer appears to be the fat wire type.
The capacitors are new.  Someone replaced the originals with Illinois Capacitor +105
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Oliver Archut

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Re: Neumann U48
« Reply #35 on: January 14, 2010, 07:31:21 PM »

There seems to be a problem with your tube, first check the cathode voltage to make sure that there is no hidden problem with the filament dropping resistor.
The x-former? First of all the B&K does not measure inductance for metal core coils proper, only air or ferrite type.
But with 160 Ohm DC? It is neither the BV8 and GN8(b) so that seems odd. Normally when a BV type x-former dies, it is either open loop ar a primary short, what translates into hardly any signal or no low end.
If you could add a closeup picture that might help to tell you more.

Pin 5 is B+ so if you disconnect the mic under load you won't get shocked.

(And that is why Neumann keeps it a bit shorter than the other pins-  if you disconnect the connector while the mic is still on, ground contact through pins 3,4, and 6 is still maintained, as B+ is already disconnected from pin 5, so you cannot get shocked. K.H.)

Best regards,

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Oliver Archut
www.tab-funkenwerk.com

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Greg Norman

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Re: Neumann U48
« Reply #36 on: January 15, 2010, 01:27:30 PM »

Thanks Oliver,
The cathode voltage looks correct (according to the schematic) 1.1V.
I will try to add a photo of the transformer when I can take a good enough one.
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Oliver Archut

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Re: Neumann U48
« Reply #37 on: January 15, 2010, 05:51:32 PM »

If the cathode voltage is proper, the only other way that the plate voltage is off is:

a) a broken capsule DC is leaking to the grid (just seen it once)
b) a broken coupling cap DC is leaking to ground via x-former and magnetize it, so not low end and sound. Saw it a few time, most of it the x-former was damaged by the DC.
c) grid leak problems (easiest to fix)
d) dieing tube, you can try to revive it but in my view wasting time and money.

Best regards,
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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.

Klaus Heyne

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Re: Neumann U48
« Reply #38 on: January 15, 2010, 05:58:10 PM »

The problem here is probably equally found in the complications of describing the flaw as it is finding the cure. Remote diagnosis of an expensive race horse's ills with such few pointers can only go so far.

I'd say off it goes, to a competent repairman.

Let us know what was found.
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Greg Norman

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Re: Neumann U48
« Reply #39 on: February 09, 2010, 03:26:44 PM »

After a break, I am back on this.  I have some new information, which some might be able to help with?

The primary of the output transformer (lifted from C4, not in circuit), has an impedance of 36KΩ @ 1kHz, when the secondary is loaded by a 1k resistor.  This was measured with multiple techniques including the first method described on this page.  Incidentally, the DC resistance of the primary is about 650Ω.
Reiterating, The secondary impedance is still 1690Ω at 1kHz, 171Ωdcr with the primary connected to amplifier circuit.  
The transformer has a label beneath the amber insulation.  On the label -  
"Neumann
Nr.
900 - 0,07
200 - 0,18"

Does this look like any of the standard transformers.  I don't see any White windings.

FYI
All passive components are newer, in good shape, and measure accurately, with 3 differences to the schematic.  C4 was changed to a 1uF cap, and R2, R6 are 180MΩ.  On my barely legible schematic, it appears like R2 and R6 should be 150MΩ?  These changes were present when this mic sounded great, and I can't see how they would be involved in lowering the plate voltage (C4 is not leaking any current, measured between 30 and 100vdc).  

Again,
Thanks for any insight.


Here is a bad photo of the transformer/mic.  I will try to get a better one soon.
http://farm5.static.flickr.com/4051/4343310193_f5403770d0.jpg
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Klaus Heyne

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Re: Neumann U48
« Reply #40 on: February 09, 2010, 04:38:18 PM »

Even on your blurred picture, the transformer looks stock.
The plate voltage on a warmed-up VF14 should be steady and between 33 to 38 VDC.

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Klaus Heyne
German Masterworks
www.GermanMasterworks.com

J.J. Blair

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Re: Neumann U48
« Reply #41 on: February 09, 2010, 07:53:23 PM »

IC brand caps and solid core wires under the basket.  This looks exactly like several Bill Bradley jobs I've seen.
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studio info

They say the heart of Rock & Roll is still beating, which is amazing if you consider all the blow it's done over the years.

"The Internet enables pompous blowhards to interact with other pompous blowhards in a big circle jerk of pomposity." - Bill Maher

"The negative aspects of this business, not only will continue to prevail, but will continue to accelerate in madness. Conditions aren't going to get better, because the economics of rock and roll are getting closer and closer to the economics of Big Business America." - Bill Graham

Oliver Archut

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Re: Neumann U48
« Reply #42 on: February 10, 2010, 12:15:25 AM »

Nr.
900 - 0,07
200 - 0,18"


Please double check if you did not make a mistake. The 200 number is right for a standard BV8, the first number should be 1300 not 900. There were several late U47 that were made with that type of transformer, that all were factory equipped with a Nu-Vistor. Neumann could never give me a straight answer if those x-former were made that way to optimise the different tube.

Also the page you quote is not the best way of measuring the impedance, in a matter of fact it is useless for talking about sound.
What I think you have a bad secondary, so a normal DC reading should answer the question.

As a reference here are some U47 x-former label info on the most frequent stock x-former.

A normal BV08 should say
1300-0.07
200-0.18 and sometimes with the addition
I rt-gn
II bl-bl

there is also the GN8(b) mostly just the type number
but sometimes with
1300-0.07
100-0.35

and very rare the GN9(b) also sometimes just the type number
1700-0.07
250-0.18

Best regards,
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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.

Greg Norman

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Re: Neumann U48
« Reply #43 on: February 10, 2010, 06:20:18 PM »

Thanks for pointing that out Oliver.  You are right.  It is
"Neumann
Nr.
1300 - 0,07
200 - 0,18"

What should the DC resistance for this secondary be?  How do you like to measure the impedance for an unknown transformer?
Thanks,
GREG

P.S. This was bought from Bill Bradley like  J.J suggested.
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MDM,

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Re: Neumann U48
« Reply #44 on: February 10, 2010, 06:28:05 PM »

did you check if there is ANY DC voltage on the primary of the output transformer??

I mean even 50 mV

otherwise polarizing voltages on capsule?

...err.. the capsule is OK right?
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