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Author Topic: XLR Phantom -> 3.5mm PIP Circuit?  (Read 4033 times)

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Offline analoghell

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XLR Phantom -> 3.5mm PIP Circuit?
« on: October 27, 2007, 08:44:54 AM »
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

Offline Evil Taper

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #1 on: November 03, 2007, 01:47:56 AM »
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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Offline Todd R

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #2 on: November 06, 2007, 12:07:11 PM »
Here's the schematic of the 48v>9v supply that DPA makes:



Be careful wiring up those zener diodes if you use this.  Put them in backwards and they will explode!
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Recorders:  Sound Devices MixPre-6, Sony PCM-M10, Zoom H4nPro

Offline analoghell

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #3 on: November 24, 2007, 07:47:33 PM »
Excellent! That's exactly what i needed. Thanks Todd.

Offline illconditioned

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #4 on: November 24, 2007, 08:06:19 PM »
Here's the schematic of the 48v>9v supply that DPA makes:



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
Please DO NOT mail me with tech questions.  I will try to answer in the forums when I get a chance.  Thanks.

Sample recordings at: http://www.soundmann.com.

Offline Todd R

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #5 on: November 25, 2007, 12:34:52 AM »
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. :)
Mics: Microtech Gefell m20/m21 (nbob/pfa actives), Line Audio CM3, Church CA-11 cards
Preamp:  none <sniff>
Recorders:  Sound Devices MixPre-6, Sony PCM-M10, Zoom H4nPro

Offline it-goes-to-eleven

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #6 on: November 25, 2007, 11:22:45 AM »
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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Offline guysonic

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #7 on: November 25, 2007, 11:48:37 AM »
+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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Offline illconditioned

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Re: XLR Phantom -> 3.5mm PIP Circuit?
« Reply #8 on: November 25, 2007, 03:38:40 PM »
+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
Please DO NOT mail me with tech questions.  I will try to answer in the forums when I get a chance.  Thanks.

Sample recordings at: http://www.soundmann.com.

 

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