Topic: 12V to power a 48V phantom powered mic?

[brownm84]

At a show 2 days ago as I was setting my rig up I accidentally hit the switch for 12V on my battery box.  I noticed it produced what the levels on my deck indicated as a good signal, but my mics (AT3031's) say they need 48V. To be safe I ran them at 48V for the show but am curious as to how 12V phantom would work as it would possibly conserve battery life on the battery box.  I'm going to try it at a show sometime where there are other tapers so if it comes out worst then I would like I can at least have another source.  Anyone tried this before? How did it work out? Thanks
Matt

[lino]

AT3031 = phantom 11V-52V

[John Willett]

Best to have it at 48V - I think the mic. takes more current if the voltage is lower.

[lino]

Best to have it at 48V - I think the mic. takes more current if the voltage is lower.

I m affraid that`s not the case with most mics
a typical input feeding resistor on 12V will be 680 ohm and for 48V 6.8Kohm which means way more current draw

[boojum]

Write the manufacturer.

[brownm84]

Thanks everybody, I'll write AT but from what I read hear I'll just stick with 48V for now.

[DSatz]

brownm, lino's response, while terse, was actually a quote from Audio-Technica's spec sheet for this microphone. What you have is basically a microphone designed for 12-Volt phantom powering. Like many other such microphones, it can handle higher voltages as well--in this case, up to the standard maximum for 48-Volt phantom powering (which is 52 Volts).

A-T gives just one value for the current ("3 mA typical") regardless of the voltage. This suggests rather strongly that 12-Volt powering would put less of a load on your batteries.

Some microphones are that way while others aren't; some draw more current at higher voltages (e.g. the original AKG C 451 E) while others draw more current at lower voltages (e.g. Schoeps CMC 6-- series). Even the same manufacturer may offer a mixture of different circuits. For example Schoeps CMC 6-- amplifiers draw 8 mA at 12 Volts and 4 mA at 48 Volts, while their VST 62, which also runs at either voltage, draws 4 mA per channel either way. It's a case-by-case kind of thing; you have to check the manufacturer's specifications.

The big unknown is your power supply. A lot of "semi-pro" gear doesn't conform to the IEC standard for phantom powering. When you switch voltages on your supply, are the feed resistors also being switched to the proper values for that voltage? That requires a switch with more contacts, which in turn could drive up the parts and wiring cost by as much as half a dollar (gasp!) for two channels--thus practically guaranteeing that some bean counter will demand either a technical compromise or the even more common "let's ignore the problem and hope nobody finds out" type of approach.

--best regards