how do i get phantom power.

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bantam
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how do i get phantom power.

Post by bantam » Tue Nov 23, 2004 5:51 pm

I built the tapeop mic pre (jfet) and something has got me. The schematic tell you that a 48V power source is required if you want phantom power. The circuit uses a 22V wall wart. Is there any way to get the 48V from the wall wart without screwing up the voltage/current going to the gain stages?

I can't see anyone using a separate power cord/wall wart for this, and i know many small preamps run one wallwart for phantom and the gain stages (bellari mp105, fmr rnp, etc...) anyone doing this?

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Re: how do i get phantom power.

Post by AWright418 » Tue Nov 23, 2004 6:22 pm

The simple answer is no. If you search around you can probably find a schematic for a 48V supply that you could build. I think that would be the best option..

Aaron

www.wrightamp.com

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bantam
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Re: how do i get phantom power.

Post by bantam » Tue Nov 23, 2004 8:53 pm

yes, i actually did find one....
http://www.tangible-technology.com/tube ... rying.html
but this, like others, requires a 120V AC input. i was trying to avoid having a wall wart and a 120V plug coming out the back of my preamp.... Anybody konw how FMR et al get circuit voltage (22V DC) and phantom power (48V DC) out of the same wall wart.

the article i mentioned claims that most condensor mics can run on anywhere from 9V-48V. Could i just tap the 22V off of the wall wart and use that to trickle current to the mic through bias resistors?

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Re: how do i get phantom power.

Post by Professor » Tue Nov 23, 2004 9:19 pm

Many pomanies that make inexpensive preamps simply don't send 48v down the line. It's not at all uncommon for preamps to output 9v, 12v, or something else that is lower than 48v.
Most microphones will still run on this, though like any weakened supply they will lose some headroom, bottom end, etc. Companies like Neumann and Microtech Gefell always warn against <48v supplies. In the case of something like the Neumann TLM-127, the different supply voltage will mess with your polar patterns since that is how they manage the remote switching. In the case of the Gefell M-930, they take the 48v to a light source that illuminates 8 little 10v photo-cells to up the voltage to 80v which is what the mic actually uses internally, so the lower powered light source means less than 80v to the capsule.

As for the single power supply problem, you could try really hard to find a PSU that outputs both 48 & 22, but that seems unlikely. I personally would check to see if your preamp would be alright running at 24v instead of 22v. My guess is that it would be absolutely fine at that voltage, but you should make sure. Then just build yourself that 110v to 48v supply you found, and then build a simple balanced voltage divider that will knock the 48 down to 24+, 24-, and a ground. Then you're all set - you have the 48v for the phantom and 24 +/- for the preamp.

-Jeremy

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Re: how do i get phantom power.

Post by bantam » Tue Nov 23, 2004 9:54 pm

great thanks!!!

anyone built the tapeop#37 jfet pre? any other solutions that you've used to get phantom power? (great super furry animals record, every time i write that i start singing it in my head)

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