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+/-15V from +48V Phantom
+/-15V from +48V Phantom
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Old 6th August 2009, 05:35 AM   #1
Pilbromatic is offline Pilbromatic  New Zealand
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Default +/-15V from +48V Phantom

Quite obvious from the title I hope!

Basically, I'm after some sort of schematic to be able to get a 15-0-15 DC supply from +48V phantom. Heck, is this even possible? I think it is...

I just want a versatile schematic that I can implement into preamps for DI boxes, mic pres, etc...

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Old 6th August 2009, 03:50 PM   #2
Nisbeth is online now Nisbeth  Denmark
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+/-15V from +48V Phantom
You can get off-shelf DC/DC modules that will do this relatively easily, but I would be concerned that a phantom supply couldn't provide enough current to do this reliably. IIRC a mic requires around 7mA from the phantom supply which isn't exactly a lot of current unless it's a mains voltage and you are standing on a wet floor....

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Old 7th August 2009, 09:38 AM   #3
mobyd is offline mobyd  New Zealand
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BSS (who made a couple of types of DIs) used a CMOS 555 (7555) driving a transistor driving a little pulse transformer (amazingly, available at RS components) to generate isolated power. Various condenser mics (AKG etc) have phantom driven DC/DC converters. The maximum available power from a single phantom powered mic line is around 150 milliwatts. You will run into the contradicting op amp requirements of low noise, fast slew and low power (choose any two :-) ).
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Old 7th August 2009, 07:04 PM   #4
scott wurcer is offline scott wurcer  United States
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You get +48V on two 6.81k resistors so by 10mA (5mA/side) you are down to <14V. If you are not using much Isupply you could make +15V in the conventional way and use one of those flying cap doublers to make -15V. There are a lot of sites with ideas for the classic Schoeps transformerless mic circuit, it's a good start.
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
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Old 9th August 2009, 05:46 AM   #5
Pilbromatic is offline Pilbromatic  New Zealand
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Cool, thanks! That's a bit of info to get me thinking, atleast! I didn't put too much thought into the current side of things, but I assumed this wouldn't be an issue, unless I were to be running several ICs off the one line.
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