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Thread: Phantom power for one mic makes other mic quiet

  1. #1
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    Phantom power for one mic makes other mic quiet

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    I am a newbie to this forum and also to recording. Just getting started with learning to record acoustic guitar with a microphone into a Focusrite Saffire PRO 14 with Garageband. SM57 sounded okay but I just received an SM81 yesterday. There are aspects I like of both, but neither one is wowing me. Of course I have more experimenting to do, but wanted to try recording through both at once to see how that sounded. The SM81 requires phantom power to be engaged on the Focusrite, but once I engage it the SM57 immediately gets quieter. Is this just a Garageband issue? Or is this a common thing to have phantom power make a mic that does not require it get quieter? The SM57 records just fine until I turn the phantom power on and boom it goes extremely quiet in Garageband. The signal to the Focusrite seems just fine based on the lights on the interface, as well as the lights in Saffire MixControl. Any advice is most appreciated!

  2. #2
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    Subscribing to see how this turns out. Never had this happen in any of the gear I've used.
    Welcome to the site by the way.
    Placebo stomps 96k ....... Recent projects
    Ray Catfish Copeland 'Got Love Jim Goodman 'Southern Steel

  3. #3
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    If the level on the meters on the SM57 channel drops seriously when the phantom button is pressed, something is wrong. The only thing I can imagine is that the phantom power circuit itself is either faulty or poorly designed. It is true that the presence of the two resistors across pins 2 and 3 does pad the microphone but it's a very minimal change - a typical 57 is around 300Ohms or so, and this probably changes to 295 Ohms - a tiny and insignificant change. However, there's a tiny chance of a fault - but its hard to imagine how the phantom pair of resistors could both be short, or virtually short - it would still leave one at 6K, making a small change to the impedance. The software has no link to this - so it's a mystery. Does it happen if you swap the two mics around? The SM57 will need more gain of course than the condenser, which will be much louder - but if this gain chances when you hit the switch, something is clearly adrift. I'd drop Focusrite an email.

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