[LAU] hardware: recording voice and acc. guitar

[Steve Fosdick]

On Wed, May 28, 2008 at 3:33 PM, Al Thompson <biggles58 at sbcglobal.net> 
wrote:

> Just out of curiosity, where is the 48V coming from?  There is no
> 48V available internally.  There is 12V, if you want to limit 
> yourself to AKG and Shure mics, but I wouldn't want to draw that much 
> current from a computer supply.

Presumably it comes from some kind of DC/DC converter.

There are at least three techniques that could be used:

1. A voltage multiplier involving capactitors and diodes.

2. A flyback converter where current is fed through an inductor and, 
when the current is switched off (by a transistor) a higher voltage is 
generated which can be syphoned off into a capacictor via a diode.  
Repeat at something above audio frequency.

3. Chop the DC so it is more like AC and feed it through a transformer 
then rectify and smooth the output.  Again work at high frequency to 
keep the transformer and smoothing capacitor small.

The designer of the sound card could roll their own converter along the 
above lines but they'd just as likely buy one in.  They are available 
as pre-made components in metal cans or epoxy packages.

Steve.