audiochains Posted October 2, 2006 Share Posted October 2, 2006 The other night when at work, we had a ballet performance for that nights show. All that was required was a feed from a Tascam Minidisc Player (with built in balanced XLR's) to our PA. Pluged it in to the mixing desk as you do, to find that feed comming in to the right channel was really quiet. After a quick look around I found that the phantom power switch was on and after turning it off the audio level returned to normal. Its like the phantom caused the minidisc player to not work properly. Can any one get me an explanation as to why this happened please? Cheers. Link to comment Share on other sites More sharing options...
dbuckley Posted October 2, 2006 Share Posted October 2, 2006 Sounds like the outputs on the Tascam are not phantom safe, putting phantom down them could cause damage. Advise you plug it in through the line TRS jacks so it cant happen again. Link to comment Share on other sites More sharing options...
Rob_Beech Posted October 2, 2006 Share Posted October 2, 2006 This does surprise me somewhat, I've not known any of the Tascam units have this problem before, still as David says use the line input on the mixing console to avoid any future problems. You may have selectable phantom per channel but its still not worth the risk. A similar problem can occur with some mixing desks used as sub desks fed to a larger desk for when you run out of channels. Where possible I'd use the line socket for this again or use a DI box. Some or the bigger DI boxes have a balanced input on XLR, this is another option for your scenario in case you can't use the line ins or in case your desk doesn't have them (silly as it sounds but even an ML3000 doesn't have them so it is not just smaller boards). Rob Link to comment Share on other sites More sharing options...
dbuckley Posted October 2, 2006 Share Posted October 2, 2006 You would think by now that any manufacturer that fits an XLR input or output socket should expect it to have phantom applied to it at some point in it's life. If it's an input it may end up on a copper split with something else providing phantom, if its an output it may get plugged into an input that has phantom on it. Yet still they come I was gazing at the updated (the "WZ cubed") A&H mixwiz 20S the other day, which now has a big load of line in XLRs (old 20S were phonos plus TRS, version 3 are TRS plus XLR), and I was wondering what they would think of having phantom applied to them. A&H know a bit about mixers, but the Mixwiz 20S is a kind of bastard child of the range, and maybe it's phantom safe, maybe it's not. The scary thing is that from a manufacturer as established and as competent as A&H that I would even stop to wonder... Link to comment Share on other sites More sharing options...
Chappie Posted October 2, 2006 Share Posted October 2, 2006 Usually to be phantom safe you need to purchase the transformer option at extra cost. Standard electronic balancing may not provide the security you need. Brand is also irrelevant, as you can blow up a matrix output on a top-end Midas with phantom. Question is, are you willing to pay the extra money when purchasing equipment? Link to comment Share on other sites More sharing options...
audiochains Posted October 2, 2006 Author Share Posted October 2, 2006 Just out of intrest, why doesnt phantom power affect dynamic mics? (EG sm58) What about when cascadeing mixing desks, where you put the output of one desk into the inpust of another, could having the phantom power on damage the outputs? I did this once (with a desk with global phantom ) and it worked for a long while until we started getting crackling noises and stuff from the outputs of the other desk we were sending phantom to. Link to comment Share on other sites More sharing options...
Bobbsy Posted October 2, 2006 Share Posted October 2, 2006 THIS LINK should give you some useful background on how phantom power works. Basically, the same DC voltage is fed up the XLR cable on pins 2 and 3. As long as both legs are present, a meter between pins 2 and 3 will show 0v and, since these are the signal output of the microphone no damage is done. However, if the device at the end of the cable is either unbalanced or not "properly" balanced, this cancellation effect doesn't happen. Since any decent dynamic mic will be balanced, the cancellation occurs and the mic is safe. Bob Link to comment Share on other sites More sharing options...
audiochains Posted October 2, 2006 Author Share Posted October 2, 2006 Cheers Bob. Link to comment Share on other sites More sharing options...
MarkPAman Posted October 2, 2006 Share Posted October 2, 2006 THIS LINK should give you some useful background on how phantom power works. Basically, the same AC voltage is fed up the XLR cable on pins 2 and 3, but with pin 3 fed the opposite polarity to pin 2. As long as both legs are present, they cancel each other out with reference to Pin 1. However, if the device at the end of the cable is either unbalanced or not "properly" balanced, this cancellation effect doesn't happen. Since any decent dynamic mic will be balanced, the cancellation occurs and the mic is safe. Bob (My bold)No, not AC! http://www.blue-room.org.uk/style_emoticons/default/huh.gif Don't want to be rude, but read your own link! http://www.blue-room.org.uk/style_emoticons/default/wink.gif The same DC voltage is fed onto pins 2&3 (usually a nominal 48V+). Pin 1 stays at 0V. Since both 2&3 have the same voltage, this makes no difference to the signal. Edit: http://www.sounddevices.com/tech/phantom.htm A better link. Link to comment Share on other sites More sharing options...
Bobbsy Posted October 2, 2006 Share Posted October 2, 2006 Oops my bad...original post edited to correct the typo! Basically a senior moment...that link give a fairly good explanation but has one diagram purporting to show a phantom source...but shows a sine wave superimposed. I'd been debating whether or not to go into the detail of correcting this and must have had AC on the brain! Bob Link to comment Share on other sites More sharing options...
Seano Posted October 2, 2006 Share Posted October 2, 2006 I think the sine wave in that diagram is actually intended to be the signal, thats why one is 180degrees out of phase with the other - there's a little red squiggle that represents a noise spike, and I guess that's intended to show how common mode noise is rejected. The diagram seems to be the view of the back of an XLR mic input to a desk (ie: as seen from inside the mixer). The phantom power is yellow, and there's a little circuit to show how phantom power is being applied to pins 2 & 3 via a pair of resistors, with a smoothing cap connected to ground. Seanx Link to comment Share on other sites More sharing options...
StevieR Posted October 2, 2006 Share Posted October 2, 2006 Just to add a warning note, Pioneer DJ mixers can get a bit upset when they get phantom up their balanced outs. Steve Link to comment Share on other sites More sharing options...
audiochains Posted October 2, 2006 Author Share Posted October 2, 2006 I think it might be safe to say make sure your phantom power is off unless you need it.The fact is there is to much gear out there (that doesn't need to be phantom powered) which will react differently to phantom power, some worse than others. :) Link to comment Share on other sites More sharing options...
gingertom Posted October 2, 2006 Share Posted October 2, 2006 Just to add a minor point to this (which should probably appear in "Pet Hates"), at the end of a job I usually insist that a desk is reset. Additionally if I hire in a desk I always check that the desk is in a basic reset state before I apply mains or other connections to it. On various jobs working with semi-pro kit I'm sure it has saved a few incidents, for what is only a couple of minutes. £0.02 Link to comment Share on other sites More sharing options...
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