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Remote pattern control and DC powering
Author: David Satz
Date: 05/04/2006
Herman, if this circuit diagram is the right one, and if I'm awake and in the real world as I write this, then the CU 48 has direct, unfiltered connections from input to output for audio signals from the microphone.

The two people whom you mentioned have excellent reputations; also, one of them is someone I happen to know and like. But this is simply a question of whether four points in a circuit are, or are not, connected to four other points, so that should hardly matter.

The DC voltages for polarizing the SM 69's twin capsules also determine the directional patterns of the capsules, so the voltages are generated in the power supply according to the specific patterns that you set. That DC flows through special wires in the SM 69's twelve-conductor cable, and isn't superimposed on the audio signals, so it never needs to be filtered out. The SM 69 has output transformers in both channels; when DC from the phantom powering reaches its outputs, they aren't affected. And any preamp, mixer or recorder that supplies phantom powering must already have some way to keep that DC from causing problems at its inputs.

Thus there is no necessity for the CU 48 to filter DC from its outputs (e.g. with additional capacitors or transformers), and it doesn't do so--its outputs are "direct coupled." In fact, to introduce unneeded coupling components (capacitors or transformers) could actually cause the exact kind of problem that people have been warning you against.

--best regards  
 
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