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Gabevee 29th July 2005 03:25 AM

Using the phantom power
Hello all!

I want to make a preamp to put into my microphone that will be powered by the phantom power.

If I recall correctly it comes through a 6.81K resistor on each leg.

My problem:

Does the 48 volts drop through those resistors? IOW, if I need to draw 4 mA, will it drop the voltage? That means it drops 27 volts, and I only have 21 volts to play with.

Is that so?

Thanks so much in advance for your replies.


Enzo 29th July 2005 05:43 AM

Yep, Ohm's Law. Those resistors limit current to a handful of mas. So 4ma will drop it to about half as you describe. But with "only" 21 volts to use, there is still plenty of headroom for any mic signal I can imagine.

Gabevee 29th July 2005 06:32 AM

Thanks so much. I was afraid so... I am using MOSFETS and the ones I use require 3 volts just to turn on.

I have the circuit designed to get 12 volts... so I think I will be OK. Just wanted to be sure.


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