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Topic: Headset mic and mixer with phantom power (Read 16667 times) previous topic - next topic
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Headset mic and mixer with phantom power

I have a headset (headphones + microphone), Teac HP-2:


As you can see the mic (pink) connector has a 3.5mm jack (like for stereo headphones).
This works just fine if I plug it into a Soundblaster Live's mic input.

But if I plug it into the line in (TRS) of the mixer (Xenyx 802) it produces no sound at all, even at full gain.

I guess this is because the SB Live actually supplies some power to the mic, while the line in of the mixer doesn't.
So I was thinking of connecting the mic to the XLR input on the mixer (through a TRS to XLR adapter) and using it with phantom power (+48V).
Specifically, I was looking at getting this adapter.

Would it work?

Could anything go wrong?

Headset mic and mixer with phantom power

Reply #1 –
I strongly suspect you would fry the mic in a heartbeat.

Those little mics are usually electret condensers that require just a few volts to run their impedance-matching preamp - +5 VDC is the norm, often referred to as "bias voltage."

+48 VDC is for "real" condensers - or professional-grade electrets - and *must* be sent down a balanced line.  If you short either signal leg to ground - which connecting to that 1/8" TRS could very likely do - you'll be shorting the +48 VDC supply straight to ground.

Edit:  Well, not *straight* to ground - most (all?) phantom power supplies have current-limiting resistors in series with their connection to the two legs of the balanced input in order to save the supply in case of just such an emergency...but it still wouldn't be happy about it.
"Not sure what the question is, but the answer is probably no."

Headset mic and mixer with phantom power

Reply #2 –
You can use a DC-DC conversion circuit to convert the -48V to +5V Bias.

This link should be a good hint on how to set this up.  I used one of these back when I DJ'd.

Headset mic and mixer with phantom power

Reply #3 –
Thanks guys.

I don't think I'll be messing with circuits for now, but out of curiosity: what's -48V in practical terms? Would I just use the XLR or would I need some outside power, like batteries?



ps, I also found two threads discussing this:
http://forum.audacityteam.org/viewtopic.php?f=27&t=5569
http://forum.audacityteam.org/viewtopic.php?f=27&t=42724

Some DIY stuff, but also a commercial solution: http://www.naiant.com/naiant/inlinedevices.html (PFA)

Headset mic and mixer with phantom power

Reply #4 –
If you want to use the mixer, I think the best solution is to get a professional communications headset (the kind that football coaches wear) or a performance mic (the kind that Madonna wears) rather than a computer gaming headset.    Or use a separate low-impedance mic.  I think you can get a mic that clips onto a regular pair of stereo headphones.

Or depending on what you're trying to accomplish, maybe you can plug the mic into your soundcard, and the mixer into your soundcard's line-input (assuming you're not using a laptop without a line input).

Computer mics and computer mic-inputs are just not compatible with pro mics and pro mixers/preamps.  Besides the power issue you've got an impedance issue.  All pro recording & performance mics are low-impedance balanced (3-wire XLR), whereas computer mics are high-impedance unbalanced (2-wire).    You can use an impedance-matching transformer with dynamic (non-powered) mics.  But for high-quality audio, it's best to avoid the computer's mic input and computer mics and go pro (low impedance) all the way.

Unlike condenser mics & electret condenser mics, dynamic mics don't need power, but in any case, with your mixer you need a low-impedance balanced mic.  Most stage-performance mics are dynamics (i.e. the famous Shure SM58).  Most studio mics are condensers.

Quote
what's -48V in practical terms? Would I just use the XLR or would I need some outside power,
As keltor suggested, you should be able to use the 48V supply (from the XLR connector on your mixer) to derive 5V, if you were going to build a circuit.    Depending on how much current you need, and how much current you can get from the 48V supply, you might be able to use a simple voltage divider (2 resistors), or a voltage regulator which is somewhat simpler than a DC-to-DC converter.

Headset mic and mixer with phantom power

Reply #5 –
Regarding 48V: I was wondering about the -48V, since the mixer's phantom power is +48V.. is it simple to get from + to -?

Headset mic and mixer with phantom power

Reply #6 –
Phantom power is definitely +48v. I think there is a solution that makes use of a resistor to reduce the +48v to something more suitable for a multimedia mic. However I can't for the life of me remember where I read about it :/

Headset mic and mixer with phantom power

Reply #8 –
For a simple solution, run your microphone into a computer or laptop, and then run the computer's output to a line-in on the board. Set the computer's microphone input to monitor (or in the speaker/output section, turn up the microphone)

Headset mic and mixer with phantom power

Reply #9 –
I've got the same problem and have never discovered a commercially available solution, probably because of the impedance issues mentioned by Doug.

Some readers may be interested in knowing that the bottom end of the EMU range of outboard soundcards (0202/0204) comes complete with a 1/8" minijack socket that supplies +5V on the ring terminal. They are only $100 or so and decent quality for the price but it's not a solution unless you are prepared to spend more money or designing a system from scratch. Could form the basis of a nice little mixing and recording system if you were interested though.