Members gismo recording Posted March 31, 2017 Members Share Posted March 31, 2017 I believe I read that you should never plug in or unplug condenser mics while phantom power was on.I try to always do this but I have accidentally plugged or unplugged a time or two and it doesn't seem to have hurt the mics. Link to comment Share on other sites More sharing options...
Members Anderton Posted March 31, 2017 Members Share Posted March 31, 2017 It's always "good practice" to make connections before applying power (or turning up the volume), and I try to follow good practice. So I can't recall plugging in with power on, which means I can't comment on whether it would make a difference or not. Phil O'Keefe knows everything there is to know about mics, so maybe he can provide an answer. Link to comment Share on other sites More sharing options...
Phil O'Keefe Posted March 31, 2017 Share Posted March 31, 2017 I believe I read that you should never plug in or unplug condenser mics while phantom power was on. I try to always do this but I have accidentally plugged or unplugged a time or two and it doesn't seem to have hurt the mics. You won't hurt a condenser mic this way, but you could damage something else (speakers) due to the loud "pop" that may result... OTOH, it's very smart to avoid connecting anything with the channel turned on... always make sure it's muted first. Oh, and there IS one case where connecting a mic with the phantom power engaged could damage the mic and that's with some older ribbon mic models. You could potentially blow the ribbon. For that reason I've always been in the habit of disengaging phantom power until I have everything connected, then engaging it. I recommend that others consider doing likewise on a fairly regular basis. Link to comment Share on other sites More sharing options...
CMS Author MikeRivers Posted March 31, 2017 CMS Author Share Posted March 31, 2017 You learn pretty quickly about the pop in the speakers and the VU meters hitting the pin when you plug in a condenser mic with phantom power switched on, And you'll also learn pretty quickly about the same results when the mic is plugged in and then you switch on the phantom power if you have the channel gain turned up. But the real problem with hot-plugging a phantom-powered mic has to do with blowing the IC input stage of the mic preamp. The inrush of current charging both the capacitors in the mic and the capacitor at the input of the preamp stage that isolates the IC from the phantom power DC causes a voltage transient that can zap the junction of the transistor at the input of the IC. This wasn't a problem in the days of tube mic preamps and solid state preamps with a transformer-coupled input, but it reared its ugly head with the low-budget mixers of the early 1980s like the Biamp and early Mackie mixers. Nobody ever thought about it back then, mostly because there were so few condenser mics that were affordable to those who could only afford those mixing consoles. Eventually they figured out what was happening and put diodes between the input pin on the IC and the + and - (usually) 15 volt power supplies to clamp the maximum voltage that pin could see to 15v, and that saved the ICs. The full scoop with graphs and circuit designs is at: http://thatcorp.com/datashts/AES5335_48V_Phantom_Menace.pdf and http://thatcorp.com/datashts/AES7909_48V_Phantom_Menace_Returns.pdf Since someone is bound to ask, I'll mention this, too. Plugging in a dynamic mic with phantom power turned on has a different failure mode, this one much rarer, but it can blow the microphone. The most guilty are classic ribbon mics that were originally built with the center tap of their input transformer connected to ground, if one signal pin of the XLR connector makes contact before the other one, the 48v is applied across the mic input. This makes the mic act like a loudspeaker and you know what can happen to a speaker if you overdrive it. For a while there was a belief that the current pulse magnetized the input transformer (of either the mic or the preamp) core, resulting in non-linearity because it inessence applied a DC bias to the transformer. Nobody ever mesaured such magnetism, however, and now that's mostly a good story to tell when you don't have any other good reason for something going wrong if a dynamic mic has inadvertenly been "phantom powred." Most dynamic mics are rugged enough to survive the voltage transient, and hardly any surviving long-ribbon mics still have the transformer center tap grounded (which is why they survive). No modern ribbon mic has a center tapped transformer except perhaps for powered mics, but they've figured out how to deal with carelessness. However, a cable with the shield shorted to one of the signal pins, or intentionally using a single-conductor ("unbalanced") cable will also apply the full phantom voltage across the mic element. Link to comment Share on other sites More sharing options...
Members philboking Posted April 3, 2017 Members Share Posted April 3, 2017 This last one is why I don't do it. You never know if a mic cable is bad. And using your condenser mic to test them is not terribly smart. Link to comment Share on other sites More sharing options...
Members gismo recording Posted April 3, 2017 Author Members Share Posted April 3, 2017 Thanks for the replies. I learned a lot. Link to comment Share on other sites More sharing options...
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