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I recently acquired an audio interface (Behringer UMC22) and, since it's quite a bit better than my motherboard, I'd like to connect my modmic 4 to the XLR mic input. The interface has phantom power available, but it's either off, or 48V, which is way too high. This leaves me with two options: inject 5V of bias power and then connect it to the XLR input with phantom power off, or drop that 48V to a more usable 3-10V.

Which option would lead to a better signal? And which would be easier to implement?

If I was to go with injecting bias power, would a 9V battery provide the best low noise power, or would 5V from the computer also do well?

This looks like a very simple way of adding bias power, I'm just wondering if everything is safe (on the interface) and how to properly connect to the XLR balanced input?

schematic diagram

Mic specs

PS: Sorry for all the questions, I found a lot of information, but none that's really complete for this use.

Sto Cristian
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  • Battery will work as well as any power source of correct voltage. However battery is most low noise source. Other ones might introduce noise to audio signal, so extensive filtering is required. – fifi_22 Jan 30 '21 at 18:24
  • i see, and i'm guessing extensive filtering is more than just a few capacitors and maybe an lm7805 right? – Sto Cristian Jan 30 '21 at 19:25
  • Yes - 7805 with caps and inductor is sufficient i think. – fifi_22 Jan 30 '21 at 19:47
  • oh well that's good. It's easy enough to implement. Now just got to get the rest figured out – Sto Cristian Jan 30 '21 at 19:57
  • Just make sure to use 50V caps (inline with micro), and check voltages before connecting any valiable hardware, then it should be allright. – fifi_22 Jan 30 '21 at 20:36
  • well if I'm just putting in external power at about 9v (to account for any possible loses and still get the full 5v), then they'd only really need to be about 13V. I'd agree if i was dealing with the 48v phantom power tho. Definitely will measure everything, even have an old mic to test with. – Sto Cristian Jan 30 '21 at 20:53
  • Is there a reason you won't simply buy a suitable adapter? There are adapters that convert the XLR connector with 48V phantom power to a standard 3.5mm connector with small enough bias for electret mics. – Justme Jan 30 '21 at 21:00
  • because it's about 40$ to get one around here. Might aswell change the mic at that point – Sto Cristian Jan 31 '21 at 00:15

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