[sdiy] General Mic supply question

[Peter Blackett]

Dear Paul,
I think the accepted standard is 48 volts ,but it is possible that some
mics may work ok on a lower voltage, some won't work correctly.I think
if you use a lower voltage then you may get less headroom if the mic
includes a preamp inside it.I think a lower headroom will mean that the
mic will distort/clip if the input signal ( in sound presure terms ) is
too great .
I know that current consumption of some older mics ( Neumann ? ) can be
quite large , so you do get problems with some makes of mic
preamps/mixers not being able to supply enough current.
there is probably an AES standard for all of this but I don't know for
sure 
regards Peter  

Paul Schreiber wrote:
> 
> 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.