Classic/Model I/Phantom Power

Phantom Power

Hilmar-at-Bose posted a great message about phantom power (and why the Bose system is 24 volts).

Let me add some technical ramblings to the 48/24 discussion. Condenser microphones require phantom for a couple of reasons

a) power an internal pre-amp

b) supply polarization voltage to the capsule

c) run an internal DC-DC converter that in turn fuels either preamp, capsule or both

Most condenser mics fall in category a). In this case, reducing the phantom from 48V to 24V has virtually no effect. In theory you can get higher voltages out of a 48V supply, but at this point you would clip the input of you mic preamp anyway.

In category b), the effect of dropping the phantom is that the overall sensitivity of the mic goes down by 6 dB. On the other hand, the max SPL goes up by 6dB. In general, you will simply have to turn up the trim a little more, but there shouldn't be any other effects.

Case c) is basically hit or miss. Either it works just fine or it doesn't work at all. I don't think there is any in-between.

Again, most mics these days fall in category a) and that's one of the reason why the the International Engineering Consortium (IEC) in it's standard 61938 (1996) in section 7.4.5. explicitly recommends

quote: Although 12V and 48V systems are still in use, 24V systems are preferred for new developments

and that's why we've chosen 24V.

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