And that was OK back when phantom power came from the backup lights, powered by enormous lead-acid battery banks in the basement.
Some phantom power systems these days, only provide 24V, or even 15 or 12V. And that is definitely not enough for some mics.
Don’t forget that a lot of interfaces have two mic inputs. And two times 10 mA @ 48V, is almost one Watt. That leaves only 1,5 W for the ADDA and the mic & headphone amp, providing the charge pump has a near to 100% efficiency. And most decent mic preamps don’t run on 5V, but need 12-32V, so you need a second charge pump…
Besides, if you draw more than 10 mA, the voltage will cave in because of the 6,81 kOhm resistors in each leg of the mic connection in the preamp, followed by another pair of 2k2 resistors in the mic. Totaling around 18 kOhms in series with your 48V power supply. Can you do the math, Steve?
That’s why you’ll never see a USB powered interface with preamps, phantom power and more than two channels. And a USB “dongle” like the XR2U is basically the same problem, only for one channel. With a preamp running on 5V. No headroom, lots of noise, hence low gain.
When it comes to extremely low noise mics, there’s two that spring up: the Rode NT1 and the CAD S100. Both exist in a USB version. Have you considered those?
I have a SEX. It’s a nice mic, but not the one with the lowest noise in my drawer. And I would certainly not use it for voice. Too bright.
The best USB adapter for a single mic is probably the Centrance Pro, but it’s like 200$. And for that amount, you can get better interfaces…
What about a Behringer UMC202? It’s around 40€. Or is that too big? Quality wise, it should be as low in noise as the Centrance.
And you can use it with any mic.
If you want far better, there’s always Sound Devices. But those are around 2.000$. Or RME, from 750$. Certainly a little less noise, a lot more gain. But I don’t think you need these for a voice/radio job that’s limited to what, 5 kHz? 15 kHz?
And you’ve made me curious. Why does it need to be very low-noise? Is that because it is FM radio broadcast, or is it HAM and you are doin’ some kind of processing?
I can’t imagine needing better than -60 dB noise floor for CB radio
Does that even still exist?