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DIY - Neumann U-47 Condenser Microphone Power Supply (for up to 6 microphones)

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FEATURES
  • +105V DC output voltage
  • less than 200uV output ripple & noise
  • capable of feeding simultaneously six microphones (50W)
  • foldback current limiting (withstands constant short circuit)
  • soft start
  • uses standard easily available components
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RESTRICTIONS
Free for private non-commercial use

Background

There is still a considerable number of original, refurbished and "copied"  Neumann U-47 microphones in use in studios all around the world. Modern large diaphragm microphones rarely produces comparable "deep" and "warm" sound.  The original power supplies for these microphones are not available as easily as the mics themselves. And if available - they probably have dried out electrolytics and can be hazardous due to very old mains transformers. Therefore there is a need for a modern but suitable power supply, that can be built to perform better than the original.

About the circuit

The raw AC-voltage needed as input for this circuit comes from a transformer, preferably a toroidal type (due to the small stray magnetic field), that has an 110..120VAC secondary, and suitable primaries according to your region voltage (100/115/230VAC). The transformer power ratings should be chosen accordingly, at about 8W per microphone you indent to drive. Feeding 6 microphones thus requires a 50W transformer. 

Following the transformer there is a plain vanilla full wave rectifier (D1-D4, use 1A and at least 200V types - as 1N4003..1N4007) that connects to the smoothing electrolytic capacitor C2. This capacitor is rated at 330uF/200V for 6 microphones, but the capacity can be smaller if you drive fewer mics. A one microphone PSU could do with a 68uF/200V capacitor.

The trick to achieve the small output ripple (<<1mV) is to connect TWO regulators in series, so that the second regulator is referenced to the first. In this circuitry the first regulator is the N-channel high voltage power MOSFET transistor M1 (IRF450). This transistor handles the pre-regulation and handles the biggest voltage drop. The second regulator that regulates the final voltage and limits the maximum current is the well known LM117 (or the commercial equivalent LM317 with slightly less voltage precision). The maximum voltage across this regulator is 40 volts, but is limited here totypically 12 volts, but at maximum to 18 volt

Mechanical construction

Coming soon...

Test and setup

Coming soon...

THIS WEBPAGE IS UNDER CONSTRUCTION, PLEASE COME BACK SOON.

WARNING! Mains voltage circuit! 
The power supply outputs a hazardous voltage so please be very careful during constructing, testing and using this unit!