Switchable Condenser Microphone

Zero Hour

The U 47 is the first Neumann microphone developed after the Second World War. Instead of reissuing pre-war models, Georg Neumann decided to make a fresh start, since tube technology in particular had made enormous progress. This meant that the housing could be designed comparatively compact – by then standards. The electronic polar pattern switching between cardioid and omnidirectional was a complete novelty. It was thus no longer necessary to replace the capsule head, and the capsule could be integrated into the microphone housing. This was the birth of the modern studio microphone. 

Larger than Life

The transducer chosen was the M7 dual diaphragm condenser capsule, which was developed back in the 1930s. This was originally offered as a cardioid option for the “Neumann Bottle” CMV 3. But just how far ahead of its time this sophisticated large diaphragm capsule was, could not be heard until it was used in the U 47, which brought it to full fruition. For in addition to making the polar pattern switchable, the technical perfection of its tube circuitry was also revolutionary. In combination, the result is a magic of sound that is unparalleled: The U 47 adds a noble sheen to voices and instruments that often makes the recorded sound even more beautiful and “larger” than the sound source itself.

Technical Perfection

What is often overlooked beyond this sonic magic is the underlying technical perfection. Yet it forms the basis for the U 47's ability to captivate us to this day. As early as the late 1940s, the U 47 achieved a signal-to-noise ratio that is beyond reproach even today. An important factor in this was the mythical VF 14 tube. Contrary to common belief, it was not a receiver tube for old “Volksempfänger” radios or even a "surplus military tube”. Quite the opposite: The VF 14, introduced by Telefunken only in 1947, was a comparatively expensive “special request” tube. One of its unique features was an unusually high heater voltage, which made it possible to operate the U 47 with only one voltage, which was used for both the heater and the anode supply. This simplified eventual battery operation and allowed long cable runs without readjusting the heater voltage. The longevity of the VF 14 tube is also legendary, as it has been in service in many U 47s for decades.

Telefunken not only manufactured the tube. In the USA and several other countries, the giant corporation also acted as a distributor for Neumann products. In the process, the Neumann badge was replaced by the Telefunken logo, which is why some associate the U 47 with Telefunken. In fact, all historic U 47s were developed and manufactured by Neumann.

Evolution

Over the years, some details were improved. Towards the end of the 1950s, the housing could be shortened by 23 mm to make the U 47 a bit more compact. Which is why U 47 connoisseurs talk about “long body” and “short body” versions – apart from cosmetics, both are identical. Around the same time, the basket was changed from polished nickel to satin nickel, which was of advantage especially for film and TV use, to avoid light reflections. At the End of the 1950s, the M7 capsule was replaced by the K 47. This was a re-engineered version using same capsule acoustics. A major advantage of the K 47 capsule is the use of time-stable polyester diaphragms instead of the PVC material previously used, which became brittle over the years. Sonically, both capsule variants are very similar.

The Myth Persists

Ultimately, the legend of the U 47 defies any attempt at explanation. Myths surround each of its components: from the M7/K 47 capsule to the VF 14 tube, the BV 08 transformer to the MP capacitors. And yet the U 47 is more than the sum of its parts. It is the perfect interplay of all of its components, as well as the hard work of Neumann engineers, that has made the U 47 a true legend. You must have used and heard the U 47 to understand what makes it so magical. 

The U 47 remains the foundation of the Neumann sound to this day. After the VF 14 tube was no longer available, a transistorized successor, the U 47 fet, appeared in 1972. This was followed in 1998 by the M 147, with a similar acoustic design and a newly developed tube circuit.