Phantom Power

[HardySpicer]

What's the best way to provide 48V phantom power for a portable
battery operated microphone device. Obviously a dc-dc convertor of
some sort. Let's assume the power supply is dc 9V.If I were doing it
from scratch I would make an oscillator - step up the voltage then
rectify.

Hardy

 

[Eeyore]

What's the best way to provide 48V phantom power for a portable
battery operated microphone device. Obviously a dc-dc convertor of
some sort. Let's assume the power supply is dc 9V.If I were doing it
from scratch I would make an oscillator - step up the voltage then
rectify.

Be careful about getting the switcher noise into the audio ground.

Graham

 

[Bruce Varley]

What's the best way to provide 48V phantom power for a portable
battery operated microphone device. Obviously a dc-dc convertor of
some sort. Let's assume the power supply is dc 9V.If I were doing it
from scratch I would make an oscillator - step up the voltage then
rectify.

Hardy

If you haven't checked the actual voltage requirements already, it would be
worth doing. I have a phantom powered mike for which the rated voltage is
48v, but speced minimum is 9v. It works fine at 8v as well.

 

[Barry Lennox]

What's the best way to provide 48V phantom power for a portable
battery operated microphone device. Obviously a dc-dc convertor of
some sort. Let's assume the power supply is dc 9V.If I were doing it
from scratch I would make an oscillator - step up the voltage then
rectify.

Hardy

Try it at 9 volts. Most still work fine. I use a Behringer ECM8000
measurement mic at 9v, but the spec says 48v I believe they mean that
to be a maximum.

Barry

 

[Eeyore]

Try it at 9 volts. Most still work fine. I use a Behringer ECM8000
measurement mic at 9v, but the spec says 48v I believe they mean that
to be a maximum.

48V is one standard but many mics work on as low as 12-15V. I've yet to meet one
which works as low as 9V myself.

The phantom power resistor value may need reducing from 6k8 with the lower
voltages.

Graham

 

[Martin Griffith]

What's the best way to provide 48V phantom power for a portable
battery operated microphone device. Obviously a dc-dc convertor of
some sort. Let's assume the power supply is dc 9V.If I were doing it
from scratch I would make an oscillator - step up the voltage then
rectify.

Hardy

I was thinking of one of those tiny class D speaker amps, wired as a
wien bridge osc, with suitable lightbulb (fet stabilisation should
obviously never be used for audio into a little step up tranny
and a rectifier. Might work quite nicely


Martin

 

[Speedskater]

Try it at 9 volts. Most still work fine. I use a Behringer ECM8000
measurement mic at 9v, but the spec says 48v I believe they mean that
to be a maximum.

Barry

What happens the day you need to use a microphone that requires most of
the 48 Volts ?

 

[Barry Lennox]

What happens the day you need to use a microphone that requires most of
the 48 Volts ?

Duh, it won't work.

That's not conceivable in my setup. The only decent mic I own, and
use, is the ECM8000.

 

[Allan Herriman]

Duh, it won't work.

I once had a U87 connected to a phantom supply that was turned off
accidentally during a performance. The sound quality didn't change
noticably, but it just got quieter and quieter over several seconds as
the supply voltage died. I had the faders on the desk up full to
compensate before I realised what had happened.

It's kinda obvious when you consider how that sort of condensor mic
works. The gain of the preamp remains roughly constant but the mic
element itself has a gain that's proportional to the bias voltage.


Not all mics work that way though, e.g. an FM mic doesn't bias the mic
element with the supply voltage.

Regards,
Allan

 

[Martin Griffith]

What's the best way to provide 48V phantom power for a portable
battery operated microphone device. Obviously a dc-dc convertor of
some sort. Let's assume the power supply is dc 9V.If I were doing it
from scratch I would make an oscillator - step up the voltage then
rectify.

Hardy

just LTspicified a little P48 generator, simply to try out this
http://schmidt-walter.eit.h-da.de/smps_e/spw_smps_e.html
Not optimised at all, made most of the component values up

I've stuck a zip of it here
http://es.geocities.com/mart_in_medina/p48.zip.
Include a FFT because it took a long time to run, noise tends to be
below -90dB wrt 1V, not bad for a quick bodge


Martin