U-47 Mic Refurbish

Neumann U-47 microphone refurbish project

U-47 Microphone basic specifications

  • 35Hz to 15.000Hz frequency range
  • Non-directional and cardioid
  • 200 ohm (or 50 ohm) output impedance
  • THD <0.8% at 1kHz and sound pressure level of 110dB
  • Tube: Telefunken VF-14M (selected for low noise)
  • Operating voltage 105VDC @ 40mA
  • Connector: 6-pin Tuchel

Background

The old Telefunken's U47 tube condenser microphone is iconic. It's a vintage large-diaphragm tube studio microphone that has a smooth and sweet sound.  It was introduced in the '50s and soon became popular in recording studios all around the world. Its excellent low-frequent handling, airy high end, and switchable cardioid/omnidirectional pattern make it an ideal microphone for vocals and classical recordings alike. Here's some more info:  


https://en.wikipedia.org/wiki/Neumann_U47


The manufacturing of these microphones (and the V-14 Telefunken tube) has ended a long time ago, but getting lucky, you can still buy them (old or refurbished ones). Replicas built with newly made parts are also in circulation. The three most critical components for the original sound quality are; the microphone capsule, the V-14 (M) tube, and the output transformer. All are hard to find, and if you find original parts, they cost a fortune. If you have a non-working U47 and have a source for spare parts it is a good idea to fix the mic and either use or sell it.


  IMPORTANT WARNING  

The microphone and its cabling contain lethal voltages. I cannot be kept responsible for any injuries or deaths caused by not following proper safety measures. Please note that high DC voltages are especially dangerous!


Fig.1 Main parts of the microphone before the build started. The black blob in the middle is the rare V-14 thermionic tube. It was originally designed for and used in WW2 field radios.

Fig.2 Original microphone schematic.


Fig.X Original operating instructions for the U47/U48 microphones (click to open in a new window).

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