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Re: Difference NS 69i and NS 69k?
Author: Klaus Heyne
Date: 05/08/2006
I am quoted as follows:

"You cannot use the audio straight out of the CU 48 converter box, because you need to remove (decouple) the phantom power DC voltage from the audio (AC) before it can be processed in the mic pre."

That is the case.
Somewhere in the connection between a mic whose power supply is phantom-operated, and the board's mic pre amp, that DC has to be removed.

As David correctly states, the CU 48 does not provide DC- blocking.
And that is the issue: The removal of DC from the AC audio conductors has to be done SOMEWHERE. If not, the mic will not work- unlike the NS 69, the CU48 makes DC blocking mandatory for its operation into a mic pre.

So the DC-blocking is typically and cheaply done with band-limiting and audio-distorting de-coupling capacitors mounted before the input in the board/mic pre. (We don't need to discuss here the severity of these alterations to the audio signal)

Phantom powering, as elegant as it was conceived by Neumann, has other limitations (the other quote cited by Herman alludes to them.)

For these reasons, the CU48 box is the less desireable of the two powering options of an SM69.

At least, some of the disadvantages using the box can be avoided by connecting to a phantom powered board which uses transformer-balanced inputs instead of decoupling capacitors.

(For my work with phantom-powered mics, I use a stand-alone, high quality 1:1 transformer, in line with a high current reserve stand-alone phantom power supply box, thus avoiding the (in my opinion) biggest audible deterioration through decoupling caps)

Best regards,
Klaus Heyne  
 
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