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Re: Neumann M49 Caps/Resistors and Schematics
Author: Uwe Sattler/NeumannUSA
Date: 05/09/2012
Schematics for the Neumann M49 microphone have been emailed, from its initial NWDR proto-type with a Hiller MSC2 tube to the production versions with the AC 701k tube specially developed at Telefunken in cooperation with Neumann and the German radio broadcast community for studio microphone applications. The final version was the M49-c, featuring improved lowered self noise through self biasing the tube by achieving the positive cathode potential independent from the filament circuit. In addition, very early versions may have their output transformer with different arrangements for their windings, resulting in audibly different low to mid range response.

The resistors used at the time of manufacture were mostly carbon composition deposit types with 100 mW or 250 mW ratings. Only a few of the resistors will influence the self noise, and the trouble to replace them with modern thin film substitutes is hardly worth the effort. Also, contrary to some widespread but misinformed sources, the capacitors in the signal path are far less critical, and standard polymer film types (polyester - PE, polyphenylene sulfide - PPS, polypropylene - PP, polystyrene - PS, or polytetrafluoroethylene - PTFE = Teflon) have been used successfully as coupling and filter (decoupling) capacitors. The capacitor connecting both diaphragms of the capsule originally was a polystyrene type, and the capacitors between plate to grid and plate to ground are typically NPO ceramic types with appropriate voltage ratings.  
 
Reply
MIKAEL ANDERSSON
05/09/2012
Uwe Sattler/NeumannUSA
05/09/2012
Uwe Sattler/NeumannUSA
05/09/2012