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can a 1.5v battery-powered mic be converted to PP?


palantir

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But when you meter it, it only appears on Pins 1 + 3. All my other mics don’t have any problems cheap mics and SM58 work fine with phantom on. Joe

 

I hope you are wrong Joe. 48 V going across a dynamic mic coil (say 150 ohm in an SM57) means 0.32 amps are going through it. Which then means that you have over 15W of heating going on within each of your mics. I don't think that would do them any good.

 

Do they help keep your hands warm? ;)

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Guest joewhite903
ive edited my last post, my mixer does however only have 48v over 1 + 3 , my normal mics dont get warm beacause they like most mics are wired across 2 + 3.
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ive edited my last post, my mixer does however only have 48v over 1 + 3 , my normal mics dont get warm beacause they like most mics are wired across 2 + 3.

 

I hope you also have 48V between 1 + 2 as well - otherwise you'll have DC across the mic's output which could be bad for transformer coupled mic outputs.

 

Things won't be quite as bad as Mark says, because a properly designed phantom power circuit will have 6.8k resistors in series with the power supply to limit the current, but the DC could still magnetise the transformer if left on for long enough.

 

Both Rick Chinn and Christopher Hicks have published decent phantom power mods for mics like this on the net. Years before this, Paul White published articles in Home Studio Recording showing the same thing.

 

Cheers

 

James.

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Found an answer to my particular problem, well the phantom power one anyway, the others are best left to a medical website ;)

 

I ordered a couple of cheapo mini-boundary mics from CPC, just to make-up the shipping charge limit, really; the package came today & the mics have a XLR to mini XLR adapter included ...... and it has a phantom to 1.5v converter included - all for the princely sum of 4.59 with a free mic ;)

 

I've ordered 3 more, sharpish; Now, if I knock out a couple of sqares of 12mm ply, I should be able to plonk the 2 spare mics over the stage at the back, or even hang 'em on the side flats..........hmmm...........

 

Thanks for the suggestions, all

 

Pete

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Things won't be quite as bad as Mark says, because a properly designed phantom power circuit will have 6.8k resistors in series with the power supply to limit the current, but the DC could still magnetise the transformer if left on for long enough.

 

OK, I was over simplifying thing perhaps a little too much in order to make a point! ;)

 

If you could get 15W from phantom power it would be a very useful thing. But you can't.

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Hello!

 

I am a PA rookie, so you probably shouldn't pay any attention to my voice, but basic physics/electrical engineering

says that if you put the 48 Volts PP over two resistances in serial with x and y Oms of impedance, respectively, then

there will be 48*x/(x+y) Volts over the first resistnce and 48*y/(x+y) Volts over the second.

 

So if you measure the impedance x of the mic, then you have to put a resistance y that solves the equation

48*x/(x+y) = 1.5 in serial with the mic (in some convenient space inside the mic that you hopefully can locate), to

end up having the desired 1.5 Volts for the mic, which is to say that 48*x = 1.5*(x+y) so that y = 46.5*x/1.5 =

31*x.

 

I just wanted to pick up this, strictly speaking that's not true as you'll have a parallel resistance between x and the microphone ;)

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yes you are right niall and I am wrong - my recipy will indeed give a parallell instead of the desired serial - thanks for shreading light on this - instead the resistance should be placed outside the mic - between the two ends of a break in the power supply cable - to give a serial - but then it should work (shouldn't it) - and very simply so
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I ordered a couple of cheapo mini-boundary mics from CPC, just to make-up the shipping charge limit, really; the package came today & the mics have a XLR to mini XLR adapter included ...... and it has a phantom to 1.5v converter included - all for the princely sum of 4.59 with a free mic ;)

Um, part number please? If it's MP33713 they're £14.59, not £4.59, according to the online catalogue....

Could use some el-cheapo phantom battery eliminators for purposes, other, nefarious.

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  • 1 month later...

I'll certainly post the circuit diagram - tomorrow when me brain has half a chance of functioning:

 

Sorry for not rplying with the part no. for the mics, I thought the thread had fizzled out.

 

Pete

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I knew I had this somewhere... As James rightly said, there was an article in Home Studio Recording in July 1988. Just managed to dig it out. I'm sure the schematic will be useful.

 

Cheers, Pete.

 

http://i2.photobucket.com/albums/y24/petealcock/RadioShackPZMMod1.jpg

 

http://i2.photobucket.com/albums/y24/petealcock/RadioShackPZMMod2.jpg

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