Left: Wagner U47w Right: Old original U47
A little bit of history...
The BV8 transformer was used in most old U47 from 1950 to the end of the Neumann production line. In the very early U47's a simpler 'coil-over-coil' version transformer was used, which was a remnant from early pre-WW2 microphones. However, since the U47 had a much higher output gain and much better frequency response than most pre-WW mics, this old transformer design proved to be critical and was replaced in 1951 by the more solid BV8, which was designed especially for the U47 and could handle more output gain and a wider frequency response. The BV8 transformer was used from 1951, first in the long body and later in the short body version, until the end of Neumann's U47 production. The same transformer technique (with a different winding ratio) was used as BV11 in the M49.
As most Neumann U47 contain the BV8 transformer, this is most likely the transformer you heard or worked with before.
The BV8 in the U47 is an expensive made special section-wound coil type. This method was commonly used in top quality 50's German tube equipment like Telefunken/TAB/Siemens V72 and V76 and is not common in modern transformers any longer, since it is very labour intensive and expensive to do. Certainly the winding technique has some influence on the sonic colouration and any other transformer would inevitably make the mic sound slightly different. Also the BV8 has two individually packed coil systems instead winding one coil over the other as it is done on designs like power transformers and simpler audio transformers.
There is no doubt that it was the unique combination of the capsule, the BV8 transformer, the tube and the grille/body mechanics, which made the Neumann U47 the most loved vocal microphone over 55 years.
Our BV8 has been made to
these original specifications for
now, using the original techniques and
the original materials like the old
high-Nickel transformer lamination. Since many years
this transformer is used as the only 100%
authentic spare part to replace
transformers in original Neumann U47 and it has proven to be sonically equal to the old BV8
for more than a decade.
And no, it
is not true that the Neumann BV8 transformer rolls off at 40Hz. (I have been told
that this rather strange myth came up recently).
Here is the frequency chart of the internal amplifier of a Wagner U47w (which is identical to a stock standard U47 with the BV8). As you can see, the frequency response of the internal amp is flat within 0.5dB from 20Hz to 40kHz!
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