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I have an AKG WMS40 wireless emitter/receiver combo which I use with a condenser mic that needs phantom power and gets it from the emitter bodypack.

If I use a minijack to mini-XLR adapter cable, can I use this system to transmit any analogue signal, such as the signal coming from a headphone out minijack? Is there a danger of blowing up the device with the headphone out jack? (since the bodypack apparently provides phantom power through its mini-XLR connector).

The AKG WMS40 system also comes with a mono 6.3 mm jack to mini-XLR cable, which is supposed to be used to connect guitars to the emitter bodypack. Guitars don't need phantom power, do they? Yet it's apparently fine to use them with this system. So how does this work? Does this system automatically detect if the device you connect it to needs phantom power or not?

Thanks!

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According to the service manual (available on the AKG website) the phantom power is 3.9v and is connected to pin 3, so the microphone connector should have pins 2 and 3 shorted. If I understand this correctly, the included cable won't have this short and will only connect pin 1 (ground) and pin 2 (signal) so there shouldn't be any risk. I have used the PT 40 to transmit sound from a tablet and it worked fine.

http://cloud.akg.com/9784/wms40_service.pdf

  • I wrote AKG and they confirmed there is no risk using the provided Mini-XLR to 6.3mm Jack cable, so apraetor wasn't right about this, but still it was wise of him not to recommend doing that if he didn't know for sure. – OMA Nov 3 '16 at 11:55
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With a condenser microphone the 48-volt DC is applied to both audio lines, so it cancels out because the signal is sent as a difference between those two lines. With a headset jack the signal for each speaker is sent as the offset between a conductor and the ground line -- this is the same circuit as that used for delivering the phantom power. As a result the left and right channels will each be at 48 volts relative to ground, which can fry electronics.

TLDR: This WILL destroy the headset jack's amplifier.

  • Thanks for your answer. So I was right in suspecting it wasn't a good idea to use a headphone jack out (I wanted to use the output of an electronic bagpipe). Then why there's no problem with guitars? They don't need that 48-volt current, do they? – OMA Nov 26 '14 at 9:45
  • Voltage isn't an absolute, it's always measured relative to something else. Since the mic and guitar send their audio signal via two wires which both are at 48 volts the 48 volts cancels out when you subtract one wire from the other -- both sides are at 48 volts, so no current flows. – apraetor Nov 27 '14 at 14:54
  • Sorry to comment in this old post, but I've thought about this again and I wonder, how can a little bodypack which runs just on a single 1.2 volt AA NiMH battery give 48 volts of power over its mini-XLR input? Is that even possible? Also, I've read that AKG's mini-XLR connections use a maximum of 9 volts anyway, not 48. So is really that unsafe to plug a mini-XLR to mini-jack cable to connect this 1.2v powered bodypack to an analogue headphone output? – OMA Mar 19 '16 at 15:42
  • Voltage doesn't really depend directly on battery size; the max power delivered does. Power = Current * Voltage. Batteries are sized by power (usually mAh). It depends on the amp IC specs, but..it'll probably fry. Feel free to try, though. Some devices might survive, others will die. Either way it'll be quick, probably. – apraetor Mar 21 '16 at 3:03
  • Since you seem to really want to do this, I suggest you build yourself a phantom power blocker. There are schematics available for free, and it isn't a particularly complex circuit. You're basically going to use capacitors to isolate the two devices from one another; the caps will permit the audio signal (AC) while preventing phantom power flow (DC current). It's the principle high- and low-pass filters are built out of. – apraetor Mar 21 '16 at 15:08
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I finally wrote AKG and they confirmed there is no risk using the provided Mini-XLR to 6.3mm Jack cable, because with that cable no phantom power goes to the 6.3mm jack.

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