1.5v Electret Mic problem with 48v Phantom - diyAudio
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Old 21st October 2013, 04:52 AM   #1
didge is offline didge  United States
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Question 1.5v Electret Mic problem with 48v Phantom

Hi there, I have what seems like a really stupid compatibility issue. I bought this headset mic from radio shack: http://www.radioshack.com/graphics/u...012A_PM_EN.pdf

It is an electret condenser that runs off 1.55v and has its own battery pack. It has a 1/4" connector that I plug into my mixer. Because it is going into the 1/4" input on my mixer, the mixer treats the signal as being "line-in". I have to crank the gain more than 3/4 of the way up and turn the fader way up to hear much, and by then I've got lots of noise. So I changed the connector on the mic to XLR so my mixer would treat the input like a mic, and sure enough, I get nice results with the gain at 12 o'clock and the fader at a reasonable level, without lots of noise. But here is the problem: When I turn the phantom power on on the mixer (to supply power to other condenser mics I have), the headset mic starts chattering wildly. The mixer is made so that phantom power is either on or off for all inputs. So apparently there is no way for me to plug this headset mic into one of my mic inputs instead of line-ins (to get the gain I need) and still use phantom power for other mics.
Can someone help me understand what might be happening to cause this chattering? Is the 48v going up into the mic's built-in 1.5v circuitry and conflicting with it? Is there some way I can get around this? One idea was to eliminate the mic's battery pack and figure out a way to reduce the 48v phantom power to 1.5v for the mic, but if it isn't something small that I can just buy, I don't really want to get into making something for it. I've soldered wires to speaker terminals, but not on the level of assembling circuitry. Plus, maybe anything I could put together would have just as much noise as I get using the thing the way I've had to use it--through the line-in. Any advice greatly appreciated.
Now that I'm thinking about it, for some reason the phantom power on channel #7 on my mixer seems to have stopped working. Maybe I can just plug into that channel and it will turn what seemed like a problem into a solution. Maybe not.
Maybe I'll just buy a mic that doesnt require batteries when my mixer has plenty of power (except of course for channel 7).
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Old 21st October 2013, 08:32 AM   #2
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You could isolate the mic by using a 4u7 cap on pins 2 and 3 of the XLR plug.
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Old 21st October 2013, 09:31 AM   #3
didge is offline didge  United States
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Sescom Sescom SES-IL-PPB XLR Inline Phantom Power Blocker Phantom Power Supplies at Markertek.com

I found this. Seems like it should do the job. Should I expect this kind of thing to introduce any noise?
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Old 21st October 2013, 11:29 AM   #4
DUG is offline DUG  Canada
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http://www.murata-ps.com/data/power/ncl/kdc_mer1.pdf

digikey

Then use a linear regulator.
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Old 21st October 2013, 06:25 PM   #5
didge is offline didge  United States
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DUG, It looks like the converter only goes as low as 5v. My POS radio shack headset mic runs off 1.55v.
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Old 22nd October 2013, 12:13 AM   #6
DUG is offline DUG  Canada
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Quote:
Originally Posted by didge View Post
DUG, It looks like the converter only goes as low as 5v. My POS radio shack headset mic runs off 1.55v.
Use a linear regulator after that.
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Old 25th October 2013, 07:53 AM   #7
Katman is offline Katman  Italy
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You need something like these:
https://www.google.it/search?q=elect...=lnms&tbm=isch
They are phantom power adapters for electret microphones to be used instead of battery power circuits.

I have made the two-transistor red schematic. It works very well.
Powering microphones
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