whu 6800ohms for mic phantom pwr? - diyAudio
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Old 18th February 2009, 09:16 AM   #1
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Default whu 6800ohms for mic phantom pwr?

I'm just wondering why all phantom powers for mics have 6800ohm resistors in series? Was it b/c that happens to be about 10x the old standard 600ohms?
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Old 18th February 2009, 10:32 PM   #2
Minion is offline Minion  Canada
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P 48v standard has allways had 6.81k resisitors comeing off of the phantom supply , never heard of 600 ohm resistors on a phantom supply , are you sure you aren"t thinking abount the old 600 ohm input/input impedance standard???

anyways those resistors are there for current limiting , so if there is a short on the mic or the phantom supply you have less chance to frying your mic or your preamp, and less chance of frying yourself....

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Old 19th February 2009, 06:30 AM   #3
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Thanks. With the 600ohms I meant source (microphone) or line impedance, which was universially set to 600ohms in the old days, and the 6800 becomes the textbook 10x load.
My understanding is that the phantom power is use to bias the mic condenser capsule, and not power an actual mic preamp. Am I right about that? ...Just as I write this I realize a condenser capsule has extremely high impedance and this cannot be...it must have a preamp right next to it, at least a simple High-Z buffer.???
I guess I need to read more about mic interfaces.
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Old 19th February 2009, 04:20 PM   #4
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As you say, mikes are usually nominally 600 ohm, the phantom power resistors are part of the load resistance on the mike, so picking a value ten times higher means it doesn't load the mike.
Nigel Goodwin
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