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Is there a Phantom Power "canceller"?

Discussion in 'Recording' started by Mckey, Apr 3, 2008.

  1. Mckey

    Mckey Active Member

    So I'm just a little curious if anyone knows of a device, like a DI or something that acts as a safe guard against Phantom Power? For use with Ribbons basically. I ask because its like a recurring nightmare of mine to just slip on the phantom power button, and then "boom".
     
  2. taxman

    taxman Active Member

    Check out the Royer web site. The do's and don'ts section says don't plug in or out when phantom power is on. Other than that, is seems phantom power not an issue. Some of their mics require phantom power, so those can't be damaged by pluggin in with the power on.

    Don't know about other brands.
     
  3. pmolsonmus

    pmolsonmus Well-Known Member

    I'm going to go out on a limb and suggest that he already knows the ins and outs.

    What he's rightfully fearful of doing is plugging in a ribbon mic into a phantom powered line.

    I've got a much cheaper solution -

    Masking tape - I only have a few old ribbon mics around and don't use them that often because they're noisy. But I have them all marked with tape that says "PHANTOM ON??????" and before I plug that mic in I check and then double check.
    It's worked for me so far, but I'm don't use these out in a classical concert venue.
    My .02

    Phil
     
  4. Space

    Space Well-Known Member

    I have a white square of tape on the +48v phantom button on the board with a red circle and line drawn on it. It at least gives pause to think for a moment.
     
  5. RemyRAD

    RemyRAD Well-Known Member

    I don't know about you guys but I have plugged ribbon microphones in and out of consoles & mixers with Phantom Power On, for over 25 years and have never blown a ribbon microphone yet. I'm talking my own personal RCA 77 DX's and Beyer M160/130's here. So I have a lot to lose if that happens. But old Neve and API stuff didn't have Phantom Power switches. It was either all on or all off. And you didn't/couldn't/wouldn't shut down the console just to plug microphones in or, unplug them. Wasn't done. Didn't do. Wouldn't worry. Didn't bother. We lived through it.

    I've lost 2 Shure Beta 58's that had Phantom on the line and weren't being plugged in or out. Go figure? The only microphones I've ever had fail. Just make sure you're using GOOD CABLES! That's where the problems occur.

    Phantom Plugger Phucker
    Ms. Remy Ann David
     
  6. Boswell

    Boswell Moderator Distinguished Member

    I know commercial plugs are banned from these forums, but I think this is relevant to the topic. Last year I was commissioned to design a ribbon mic protection/preamp unit. It's currently (rather slowly) going through pre-production trials.

    I had to research quite a bit on the possible damage that phantom power can do to all types of microphone, not just ribbon. Not surprisingly, the damaging transients happen at plug-in and/or switch on of phantom power, but can also occur on unplugging, when one signal lead breaks connection before the other. As Remy mentioned, the other main source of problems is faulty cabling. Designing a device that would ensure safety at the microphone connector under all conditions of fault and power cycling while not compromising audio properties was a real challenge. I'll keep you posted.
     
  7. JoeH

    JoeH Well-Known Member

    Ditto for everything said so far; I'll just add that I've been under the impression that most phantom power supplies are very low amperage, and won't necesarily blow things up; there's just not enough current to do much damage. STILL, it's always good to keep it out of the circuitry for ribbons, etc., and as everyone has already mentioned, used good cables and be careful patching in and out of stuff.

    AEA's TRP has some kind of diode circuitry on the output that blocks phantom power in case it's plugged into something with Phantom. (It's a bit pricey for a device to just block phantom, but it IS a great stereo ribbon mic pre that will never hurt your ribbon mics. )
     
  8. Cucco

    Cucco Distinguished Member

    I don't think this would be considered banned in any way. Please keep us posted on all of the details. We really only get pissed when people come around and list an entire post (or 20) with nothing but stuff that they're selling.

    If you happen to know of a product that does a specific job and you just happen to be the maker/vendor of that product, there's no harm in mentioning or even heartily recommending it.

    Cheers-
    Jeremy
     
  9. Cucco

    Cucco Distinguished Member

    Of course, back to the OT -

    Have you considered the Rode plug? I don't recall the name/model, but it's about $99 and uses a transformer to isolate the mic from phantom all the while boosting the gain and (supposedly) leaving the signal in tact.
     
  10. Link555

    Link555 Well-Known Member

    Most people just use a blocking capacitor to block DC. But a transformer will work.
     
  11. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Well...hmmm...as long as YOU know, and somebody else doesn't grab them.

    Ned Newby.. "I guess he wants to make sure phantom power is on? :? "

    I'm guessing you make sure it's impossible for that to happen? :wink:

    Kapt.Krunch
     
  12. RemyRAD

    RemyRAD Well-Known Member

    I just knew that Boswell was some kind of crazy genius. I just didn't realize he was more sane than the rest of us? Fabulous Boswell! Please keep us posted on your wonderful new circuit. TAA! You British guys are just incredible! When I grow up... I want to be British!

    Learning to fake my British accent. Actually I can do Canadian better eh? Nothing you can do a boat that eh.
    Ms. Remy Ann David
     
  13. Cucco

    Cucco Distinguished Member

    You need to work on your dialect Remy -

    It's "a-boot"
     
  14. BobRogers

    BobRogers Well-Known Member

    If you need help working on your accent....
    [youtube:4193bef9d1]http://www.youtube.com/v/3UgpfSp2t6k[/youtube:4193bef9d1]
     
  15. rockstardave

    rockstardave Active Member

    wow that girl's pretty cute. i'm a sucker for a southern accent...
     
  16. Cucco

    Cucco Distinguished Member

    I'm a HUGE sucker for brunettes with British accents. Cockney and Irish accents too...Mmmm.

    I'm sitting here watching the first 30 seconds of the video at work and realize..."uhhh...perhaps I shouldn't watch this at work."

    Despite the fact that we're a highly evolved species, parts of me are still a dumb animal... ;-)
     
  17. Mckey

    Mckey Active Member

    Wow this thing really took off! I wasn't expecting that :)
    Hey Cucco, are you referring to the rode D-Power Plug? http://www.rodemicrophones.com/accessory.php?product=DPower_Plug
     
  18. MadMax

    MadMax Well-Known Member

    Boswell (et al),

    I had my SF12 die awhile back. Blown ribbons.... bonus.

    When I talked to the good folks at Royer, they said it looked like a power spike got the ribbons, and probably from phantom power being on at connect/disconnect.

    I asked them about any protection devices they could recommend, if they didn't make anything.

    The comment was a simple set of series non polarized blocking caps and at least a 1M loading resistor.

    I've got a prototype I'm working on, with enough supplies to build about 12 or so. If anyone is interested in either building one on their own, or if you would be interested in trying one out, let me know.

    The prototype is a two channel job for the SF12, since it's a stereo mic and fits in a box the size of a DI.

    It's been on the back burner for a couple of months since the studio build has taken off, but if there's any interest I'll get back on it.

    The components are reasonably cheap... like a coupla' bucks. The expensive parts are the XLR's and the enclosures, which are a few bucks each. My estimate is somewhere in the $25-$30 range complete including labor. Parts alone, somewhere in the $15-$20 range... less if you go with plastic enclosures.

    Not hawking a product here... I had a minimum order to get the parts, so I figured what the heck, make a dozen.

    If your interested, gimme a shout.
     
  19. Boswell

    Boswell Moderator Distinguished Member

    You have to be a little bit careful about coupling capacitors. They can be both your friend and the enemy at the same time.

    A few sums:

    (1) to get a -3dB point at 10Hz working into the 6K8 input resistance of a PP circuit, the capacitance value needs to be 2.4uF.

    (2) a 2.4uF capacitor charged by the PP circuit to 48V holds 112 uC (microCoulombs) of charge.

    (3) Under fault conditions, such as someone puncturing the cable with a chair leg and causing one of the signal conductors to short to the screen ground (this has happened to me!), the coupling capacitor can discharge through the microphone. The initial current surge value will be the full 48V through the (say) 200 Ohms of the microphone, giving 240mA. The energy of discharge is approximately 2.65mJ.

    (4) If the discharge is through a 25mm ribbon microphone having a 1T magnet, the impulsive force at the ribbon is about 6mN (milliNewtons). Most ribbon assemblies would not survive this.

    A simpler comparison can be made by comparing the generating and motoring emfs on the ribbon. A typical ribbon microphone can generate around 25mV r.m.s. at the preamp input when placed in the highest continuous sound field that the ribbon assembly can tolerate before damage. This is about 2000 times less than the 48V peak of the discharging capacitor when motoring.

    This all sounds a bit scary, but, as I mentioned, capacitors can be our friends too, as long as we respect their properties and take into account their capacity (sic) for doing damage. So, if we can spot the fault conditions and take action in time, we can use capacitors to do the job of isolating us from phantom power. That was what the contract design work was all about.

    I'm doing some direct-to-stereo recordings this week where I will have the opportunity of running a pair of condenser microphones and a stereo ribbon microphone side-by-side, making two separate stereo mixes. I'll be trying out my protection circuit/preamp on the ribbon, the idea being to see if it survives critical sonic examination, although I don't intend to rupture microphone cables just to test its protection properties.
     
  20. Cucco

    Cucco Distinguished Member

    Just curious -
    Obviously that amount of current at the microphone would be lethal to the mic, but any of it seeking a ground through, say, someone holding it would also be (VERY) lethal.

    What do you foresee as the possible conditions for this? Say the intern is placing the mic as someone ruptures the cable inadvertently??

    Pardon my ignorance about this - especially if it's a dumb question.
     

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