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Author
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Topic: Electret mic/phantom voltage?
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Bryan Bradfield
Member From: Lethbridge, Alberta, Canada.
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posted 23 November 2003 01:40 PM
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I'd like to install a Radio Shack mini electret microphone into a guitar, and power it through the phantom power of my amp, a Dean Markley KAC-30. I believe the amp's phantom power is 24 volts, while the microphone is rated at 10 volts.
Will I burn up the microphone or amp, or is there any problem with the voltage mismatch? |
Bill Crook
Member From: Goodlettsville, TN , Spending my kid's inheritance
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posted 23 November 2003 02:39 PM
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Several thoughts on your question.......As a Tech,I think a device rated for 10 volt(max) gettin' hit with 24 volts is asking for trouble.ie,like burning out the element and it would (while still alive) be so sencesative that about all sounds would be distorted far beyound any useable limits. In general, the electret mikes elements can operate extreamly well right down to the 1.5 vote range. These devices are sorta like IC chips. They can operate very well over a range of voltages but 24 volts is 2.5 times over the max. At 12 to 15 volts, I would say your are safe signal-wise. As for it hurting you amp,I wouldn't think so due to built-in current limiting resistors in your ampifier. Now,as the phantom power has a liminting resistor involved, You could have your local tech replace it with one twice the value. This would fix the excess voltage problem for you and also not hurt the performances of other phantom powered devices you may wish to use later as (like I stated) these devices can operate over a wide range of voltages. Your tech could place a resistor in the plug-end of the mike cord without haveing to make changes in the amp works,(which in my opnion,is not a desireable thing to do)as you may want to sell/swap the amp later on. A resistor in the 1/8th or 1/16th watt range will suffice as there is just micro-mill current drain here. Your tech can do the ohm's law thing to determind the correct value of the resistor needed to drop the voltage down to an acceptable level. Hope this helps a bit in your quest.  |
Bryan Bradfield
Member From: Lethbridge, Alberta, Canada.
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posted 23 November 2003 05:25 PM
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Thanks Bill. Knowing that 1.5 to 15 or so volts is a good range for the electret mics is helpful. Knowing that I can add resistance to bring down the voltage is the answer I was looking for. |
Paul Osbty
Member From: Seattle, Washington, USA
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posted 25 November 2003 02:57 PM
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I would double check your phanton power voltage. Phantom Power, on most any mixing board, is 48 volts. I didn't know DM made amplifiers, nor do I understand using 24 volts for phantom power. |
Bryan Bradfield
Member From: Lethbridge, Alberta, Canada.
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posted 25 November 2003 04:43 PM
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I'm not sure where I got the idea that the phantom power was 24 volts. Using a multimeter, I measured the power across pins 1 & 2, and also pins 1 & 3, and found it to be 7.16 volts DC in both cases. Is this normal for phantom power? If indeed I have 7 volts, then my problem with a mic rated at 10 volts would seem to be solved. |
Dave Boothroyd
Member From: The Malvern Hills
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posted 26 November 2003 04:56 AM
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You need to realise that there are two issues here.
A true capacitor Mic needs a polarising voltage to reference the signal against- to set up a basic charge on the two plates of the capacitor - one of which is the diaphragm. As the diaphragm moves, so the amount of charge that the plates will hold varies. The movement of the diaphragm thus produces a varying voltage across the plates- which is what we were all hoping for in the first place. That is usually 48 volts.
In addition, because the signal is very small, there is a little amp built into the capsule which also runs from the same power source- but at a lower voltage.
A back Electret capacitor Mic has been made with a charge already applied to the plates at the manufacturing stage, so it does not need the polarising voltage, but it still needs 1.5 volts to run the little amp.
Cheers
Dave |
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