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I just purchased a Behringer Xenyx 802 mixer and have a question about phantom power, which might be a general question--not just about the 802.

There is a "Phantom Power" switch that turns it on for channels 1 and 2. When I turn it on with my condenser mic connected, everything works great: before turning on, no power and no sound; after turning on, power and sound. However, after turning it off, the power stays on for quite a while, eventually dying off, but it takes minutes sometimes.

Is there a defect with my mixer or is it normal to have the power remain in the system for a time?

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Well, they do call it 'phantom' power (-:

A typical condenser mic presents almost zero load to the power supply, so the voltage doesn't drain away quickly when the power is switched off. Typical, and nothing to be concerned about.

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  • Do you know if it is common for most boards to do this or do only some do it? I've never gone looking to see if devices that need phantom shut off right after turning phantom power off, but I have to admit I'm kind of surprised that the board doesn't drain off the power or cut the circuit after the capacitor (that I assume must be the source of the residual power.) Do you know if there is a particular reason that they wouldn't hard cut the power since it should be possible? – AJ Henderson♦ Jun 17 '13 at 14:23
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    @AJHenderson: artificially pulling the voltage to ground quickly might cause a loud popping noise in not ideally balanced circuitry. Just leaving it to discharge slowly through the already-present load is much "safer", no hard transients. – High-end phantom supplies will both build up and cut down the voltage in a controlled, smooth yet reasonably fast fashion, but in ordinary mix preamps the manufacturers generally won't bother, when there's a so much simpler and still quite well-working alternative of just leaving the capacitor open. – leftaroundabout Jun 17 '13 at 20:39
  • @leftaroundabout - makes sense, I figured it might have to do with worrying about the pop. I don't remember the exact details of how phantom power is applied off the top of my head though, so couldn't remember exactly what might happen with it. Thanks for the detailed micro-answer. – AJ Henderson♦ Jun 17 '13 at 21:04
  • Is there any concern about disconnecting the mic before the light goes off? When I'm trying to switch mics, I don't necessarily want to wait 5 minutes. – acjay Jun 7 at 3:05
  • @acjay - there's no harm to the mixer or the mic. It'd be prudent to take the output faders down, or mute the inputs involved, so that if there is any 'pop' it doesn't propagate through to anything downstream. – Jim Mack Jun 7 at 14:21

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