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He's feeding it 24V DC, but I doubt the current draw is going to be static, it's going to use more or less power depending on what the applied signal is. I don't know how variable this is in a pre-amp so I just said RMS current to be on the safe side. If he tests it on a bench without a load and thinks he's going to get X power over the long haul and it's current use doubles with an applied load in his app he's gonna be surprised.
you are not clear in what is the doubt you have. Please plan and make a proper presentation so that a possible answer could be given. If a picture can speak THOUSAND words, why not upload a block schematic of the equipment under question in support of your query?