rodabod

Coverting Phantom Power (P48) to 12V (P12)?
« on: June 17, 2005, 08:00:57 AM »
Hi Guys,

Does anyone know a simple way of using a microphone designed for use with 12V phantom power with a 48V phantom powered pre?

I know there must be a simple way of fixing the voltage but I'm not sure of the simplest way. I don't want to bugger about with my preamps - I'd rather make an in-line converter or a cable adapter.

Thanks.
Quote from: tv
punchy fat bastard chip


clintrubber

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #1 on: June 17, 2005, 08:37:13 AM »
Depending on the actual schematic, but a 12V zener might be just all that's needed  :thumb:

Example:  D1 (here a 10V-zener is used, but OK)

Mendelt

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #2 on: June 17, 2005, 10:14:44 AM »
I built something much simpler with just a zener some caps and some resistors for a couple of sennheiser MKH416T's. As long as the mics dont eat too much current (and they hardly ever do) it works beautifully.

I found the schematic online and i posted it here somewhere. I'll see if i can find it...

<edit>
http://www.uneeda-audio.com/phantom/t-power.htm

There are two versions. One with caps and one with a transformer and a capacitor. I did the cap-coupled version with some extra film capacitors paralel to the signal coupling caps.
</edit>

clintrubber

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #3 on: June 17, 2005, 10:57:18 AM »
Quote
I built something much simpler with just a zener some caps


Hey, I didn't mean that that total circuit should be added ! I just added it to illustrate the zener !  

Most (any) phantom-powered stuff will have something like those resistors R10, R11 and once you've found these (and perhaps adjust their value a bit upwards) in the 12V-mic-circuitry you just add that single zener.

But about the circuits you added, it's indeed important to know about which kind of '12V phantom' we're talking.

rodabod

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #4 on: June 17, 2005, 03:05:08 PM »
Thanks very much for the replies, guys.

Are there different types of 12V phantom power? I assumed it would be exactly the same but 12V instead of 48V?
Quote from: tv
punchy fat bastard chip

clintrubber

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #5 on: June 17, 2005, 06:54:50 PM »
All I know for now is that (1) there are a few different systems out there that are structurally different and (2) that I'll only will be messing with P48, that's enough  :thumb:
But serious, search around here and out on the web, there's lots of info around, like for instance the link Mendelt already posted:
http://www.uneeda-audio.com/phantom/t-power.htm

CJ

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #6 on: June 17, 2005, 07:32:12 PM »
The simplest way would be to just add a resistor in series with your phantom plus voltage line going to the mic. You could build a special chord to be used only with that mic and mark it carefully so you do not accidently use a regular cord with the mic.

You would measure the current draw of the mic by hookinhg iyt up to a 12 volt supply. So let's say you found the mic to be drawing 10 ma. All you have to do is some ohm's law, and splice in the resistor.

Clue: you need to chew up 48 minus 12 volts with the resistor. What size resistor do you need to use?

What would be the power requirement of the resistor? Double it for safty reasons.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

bcarso

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #7 on: June 17, 2005, 08:07:47 PM »
Quote from: "CJ"
The simplest way would be to just add a resistor in series with your phantom plus voltage line going to the mic. You could build a special chord to be used only with that mic and mark it carefully so you do not accidently use a regular cord with the mic.

.


I could see making that homonymical error after diminishing a fifth.

Of course this could also become the Search for the Lost Cord...

CJ

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #8 on: June 17, 2005, 09:26:55 PM »
Yes, duct tape or mig weld that cable on there in case Mike Pinder wanders in from Grass Valley.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

PRR

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #9 on: June 18, 2005, 01:13:31 AM »
> a microphone designed for use with 12V phantom power with a 48V phantom powered pre?

Not necessarily. P12 is speced different resistors and more current than pre-1980 P48 power. I don't have a P12 spec handy; it may be more current than modern P48.

True P12-only mikes were fairly rare. Once you get a mike working on less than 12V, it is not at all hard to build it to take up to 52V. AKG414 takes 12V-52V and drops it all to 9V internally, directly for the amp and jacked-up to 60V for capsule bias.

What exact mike model do you have?


rodabod

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #10 on: June 18, 2005, 04:42:35 PM »
Hi, it was actually an old Gefell PM750 condenser microphone which I was considering buying. They are usually used with particular power supplies which provide 12V phantom (this might be called T-Power?).

Since there is no power supply available, I thought simplest option would be to construct a convertor box to step down 48V phantom to 12V.

I couldn't think off the top of my head if this would affect the audio signal or not, so I thought I'd ask if there is a standard solution.
Quote from: tv
punchy fat bastard chip

PRR

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #11 on: June 18, 2005, 10:53:26 PM »
> might be called T-Power?

T-power is very different.

Last time I met a T-power mike, I wired up a 9V battery and some resistors. That was nearly 20 years ago, and details are foggy.

http://www.uneeda-audio.com/phantom/t-power.htm

clintrubber

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #12 on: June 19, 2005, 04:53:35 PM »
Quote
Of course this could also become the Search for the Lost Cord...

Potential problem indeed.
Always make a second one if you're doing a non-standard cord for something. And bring it along  :wink:

verbos

    NYC (where the latest fashions be)
  • Posts: 76
Coverting Phantom Power (P48) to 12V (P12)?
« Reply #13 on: October 23, 2006, 08:15:52 PM »
Quote from: "rodabod"
Hi, it was actually an old Gefell PM750 condenser microphone which I was considering buying. They are usually used with particular power supplies which provide 12V phantom (this might be called T-Power?).

Since there is no power supply available, I thought simplest option would be to construct a convertor box to step down 48V phantom to 12V.

I couldn't think off the top of my head if this would affect the audio signal or not, so I thought I'd ask if there is a standard solution.


I know this was a dead topic, but.....

I have one of these and, although I have the power supply, I'd love to convert it to phantom power. The supply I have is 220v and a pain in the ass. Plus, I think it may be adding a buzz into the signal. I have not found a schematic for this mic, nor any real solid advice about how to do the conversion. I have never worked on a mic before, so I don't know the standard way it is done.  Couldn't you just add caps to the 2 signals and resistors on the mic side that go together, then have a 12v zener and send that to the 12V line on the mic? That much could fit inside a cable housing and not even mod the mic.

Mark

SSLtech

Coverting Phantom Power (P48) to 12V (P12)?
« Reply #14 on: October 24, 2006, 09:32:48 AM »
Quote from: "bcarso"
I could see making that homonymical error after diminishing a fifth.


...I'm not sure if by "diminishing a fifth" you mean 'altering a musical interval' or 'polishing off a bottle of liquor'...

-Just curious...

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.


 

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