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Gear / Technical Help => Cables => Topic started by: analoghell on October 27, 2007, 08:44:54 AM
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Hi,
Does anybody have a circuit diagram of something I can build to use 9v PIP mics with 48v phantom XLR recorder inputs?
I know I can buy such a thing (Sound Professionals etc) but i'd like to try it myself and also see how it's done.
Anybody?
TIA,
ac
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The recorder is supplying the phantom power? I THINK you are talking about bumping a 48v source down to 9v correct? If that's what's going on you just need to build a small voltage regulation circuit that will eat 39 volts. Otherwise why not just power the mics with a 9v source and then input the output to the recorder?
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Here's the schematic of the 48v>9v supply that DPA makes:
(http://www.dpamicrophones.com/Images/DM02113.jpg)
Be careful wiring up those zener diodes if you use this. Put them in backwards and they will explode!
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Excellent! That's exactly what i needed. Thanks Todd.
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Here's the schematic of the 48v>9v supply that DPA makes:
(http://www.dpamicrophones.com/Images/DM02113.jpg)
Be careful wiring up those zener diodes if you use this. Put them in backwards and they will explode!
Can you explain that circuit to me? It looks strange. I assume the mic goes at the left? But that is at a constant voltage, due to the zener? My head hurts...
Richard
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I think I'm in trouble if I need to explain circuits to you Richard, but yes, the mic goes to the left. :P
The DPAs are only 2-wire, not 3-wire. The zener will provide a constant voltage to the mics. I haven't looked up this zener in awhile, but I think it will provide 8.2v or 8.5v. C2 is a blocking capacitor, and the rest -- got me, filtering and balancing I guess.
I've been meaning to get the parts and make up one of these but haven't gotten the chance. I assuming though that DPA got it right. Good luck tracing it out -- let us know what you figure out. :)
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I've never done any circuit simulation but can't you throw a simple circuit like that into a simulator and then play with it using a virtual scope?
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+48 volt Phantom power from 6.8K current limiting resistors (inside the deck) appears at pins 2 & 3, with pin 2 being the + (non-inverted) signal input polarity.
What this circuit is doing is clamping the voltage for the mic at a safe level, coupling the audio signal through the C2 in-series cap going to pin 3.
The resistors along with the C3/4 capacitors to pin 1 common are being used shunt audio signal out of the - (inverting) pin 3 input and make it a 'floating DC' signal common, but with no actual audio signal going to that pin. So the deck sees only the mic signal at pin 2, and pin 3 sees only a filtered no audio DC - input reference level.
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+48 volt Phantom power from 6.8K current limiting resistors (inside the deck) appears at pins 2 & 3, with pin 2 being the + (non-inverted) signal input polarity.
What this circuit is doing is clamping the voltage for the mic at a safe level, coupling the audio signal through the C2 in-series cap going to pin 3.
The resistors along with the C3/4 capacitors to pin 1 common are being used shunt audio signal out of the - (inverting) pin 3 input and make it a 'floating DC' signal common, but with no actual audio signal going to that pin. So the deck sees only the mic signal at pin 2, and pin 3 sees only a filtered no audio DC - input reference level.
OK, I see now. Cool idea to use the Zener. Is there a noise problem with diodes, I wonder?
OK, another question. Why not have a symmetric circuit? Eg., have one side of the Zener drive pin #2 and the other drive (negative) pin #3. Perhaps there is some benefit to have the mic have a common ground with the XLR pin #1?
Richard