AudioBanter.com - View Single Post - Can you run Phantom Power to non-condenser mics?

In rec.audio.pro wrote:
Good questions Ray.....

Dynamic mics should ignore phantom power...

"Should" is the operative word here. Most do work, BUT be aware
that every now and then you find one that has the output transformer
center tap connected to ground. That shorts out Phantom power.
If the 6.8k resistors are large enough and the phantom power supply
has enough "oomph" it won't do much, but DC throught the mic
transformer windings is not a good thing.

Phantom power works by supplying +48 volts equally on pins 2 and 3....pin 1
is the ground

In a dynamic or ribbon mic the +48 volts is present on both pins so they are
nulled out. This is called "common mode rejection"

Not exaclty. What you need is for pins 2 and 3 to "float" with respect to
ground. You can use an ohm meter to check pins 2 and 3 to pin 1 and
to the mic case. It should read an open circuit for BOTH polarities
of the test leads.

Some boards have switches on each channel to disable the power. It is easy
to add your own.

Inside to board there are two 6.81K resistors that feed the 48 volts to pins
2 & 3. you can place a switch just upstream from them to switch off the
power. You can do this for each channel or in sections.

I have heard several manufactures call this mod "unnecessary", "unneeded",
"only for the uninformed" etc.

"Uninformed", my butt! I strongly urge installing these switches on
at least a couple channels so if worse comes to worse and you find you
have a couple mics that do not "float", you can put them in those
channels and turn off Phantom power.

Benj