[sdiy] RE: General Mic supply question

Czech Martin Martin.Czech at micronas.com
Fri Aug 29 19:26:08 CEST 2003

No, I do not think so.
It is only needed for capsule bias (condenser).
If you have an electret (sp?) capsule with built in E-Field
you would only need some voltage for the built in preamp.
15V is enough for a JFET, even 5V might be usable.
This is also what most battery stuff does.

But if you want a good capsule with log life time
and strong output, I guess you will need the 48V
for polarisation. The capsule itself is connected 
via very high Ohms to that (to avoid nonlinearity).
It realy needs no current other then leakage.
The preamp then has to live with the 48V, which
has also positive effects.


> -----Original Message-----
> From: Paul Schreiber [mailto:synth1 at airmail.net]
> Sent: Freitag, 29. August 2003 19:28
> To: Czech Martin; Dave Magnuson; synth-diy at dropmix.xs4all.nl
> Subject: General Mic supply question
> 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.

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