Most professional condenser mikes need a bias of around 250 to 300 volts.
Inside the mike is a dc to dc switching supply that takes 48 volts
and wanks it up to the 250 volts or so needed for bias.
Mucho filtering and usually completely shielded in a can.
The switcher doesn't need much current.
Inside the mike at the xlr 3 pin connector are two 6800 ohm resistors going
to pins 2 and 3,
then connecting together to feed the 48 volts impressed on BOTH balanced
audio wires
(with pin 2 nowdays accepted as the high side) to the dc inverter.
The way studios do this is to feed 48 volts to two 6800 resistors at each
mike input
going to all of the mike lines entering the console.
All of the above harangue is to now suggest that anyone lucky enough to have
a good
Neumann 87 or an AKG 414 may simply snap together (5 each) 9 volt batteries
(45 v. or so)
and feed the plus into two 6800 resistors and then slobber them onto pins
two and three of your XLR connector.
Maybe a spst switch if you want to have the batteries last for a year or so.
In the old days we found some noise in the recording chain from thermal
noise in the batteries,
but many field recording guys use this nowdays.
In hollywood studios we used to swap ideas to get quiet phantom supplies.
Back in 1965 we all knew each other at other studios and helped each other.
Every studio job I have had was because of a ham fellow at another studio.
Phantom away dudes!
Pete W6LAW
--
Pete / พีท
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