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Powering a 2-pole 3.5mm (1/8") connected electret microphone with a Xenyx 302USB

published Apr 14, 2017 04:30   by admin ( last modified Sep 03, 2017 11:20 )

Update 2017-08-27: This solution does work! But you can't have dirty power with mains hum in it. If you are running on a laptop and you hear hum, try disconnecting the laptop from the charger.

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There is a 3,5mm (1.8") microphone jack at the top right of the Xenyx 302USB.

It seems to be wired the same as in SoundBlaster sound cards, and have a 4V voltage for driving electret condenser microphones:

        / \ 
       |   |   Tip - Audio signal
        \ / 
       +===+
       |   |   Ring - Bias voltage for microphone (+4V)
       |===|
       |   |
       |   |   Sleeve - Ground
       |   | 
     +=======+
     |       |

Schematics adapted from: Powering microphones

However my electret microphone seems to be wired like this:

        / \
       |   |   Tip - Audio and bias voltage (+3V)
        \ /
       +===+
       |   |  
       |   |
       |   |
       |   |   Sleeve - Ground
       |   |
     +=======+
     |       |

I think it runs on 3V so 4V is close enough I guess.

So I am using a wiring block to make the ground not extend to the ring, and have the signal + voltage on both the ring and the tip, going into the mixer:

        / \ 
       |   |   Tip - Audio and bias voltage (+4V)
        \ / 
       +===+
       |   |   Ring - Audio and bias voltage (+4V)
       |===|
       |   |
       |   |   Sleeve - Ground
       |   | 
     +=======+
     |       |



Source quote for the voltage:

The 302USB does not have the higher voltage phantom power used in older mixers. It does have the 14 volt on the XLR and the 4 volt on the 1/8' (3.5 ) bias for electert mics. This is not something you can turn off but is not a problem unless you are using equipment that is not isolated or balanced and then you can get noise from cable movements, inserting plugs with the volume up. Hope this helps.

Amazon.com: Questions And Answers: Can I use this preamp without phantom power? and if so, how?

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