[sdiy] General Mic supply question

[Paul Schreiber]

I am looking into this topic right now. Here is what I've found so far:

a) the "general accepted" phantom supply is +48V, fed through 6K8 resistors
b) I think there is some industry standard (IEC?) for this.
c) However, I've seen *many* non-48V supplies! Examples:

1) 2 9V batteries in a box (18V)
2) +15V used with smaller resistors (like 2k2)
3) CMOS oscillators/charge-pump triplers (maybe +20V or so if running off +12V, 4000-series CMOS)

I guess what I'm asking is: is the +48V a worse-case thing with 300ft of snarky Hosa cable? Can I
use say +24V, lower feed resistors and be happy with powering only 50ft of cable?

Paul S.