Can phantom power of a submixer fry a PA

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candlelightvid

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Hi -- I shoot video for events, and *always* get an audio-output from the sound tech to mix with other audio sources. Sometimes this is via tape-out (RCA), sometimes ctrl-room or aux-out (balanced 1/4"), sometimes a main-out or XLR on a subgroup... always works out very well.

The submixer I use to realtime mix the inputs for my video equipment is a Mackie 12-channel mixer, and because I also mix in two shotgun microphones, I enable phantom power on the board.

Recently, the sound tech. was using an older Peavy PA/amp with some huge (old looking IMO) speakers, and the Peavy only had 1/4" connectors for the outputs. They plugged me into a main-out (I think), and had an inexpensive converter-gizmo which took my 100' XLR and converted it to 1/4" so I could take their mono output.

A little bit into the event, they the sound went out on one of their speakers and they smelled like something was burned out... turns out, their speaker got fried. They are thinking that it got fried because phantom power got sent from my board into their PA.

Is this possible? I thought that 1/4" doesn't carry phantom..?? I'd also think their PA would have fried before sending the power back out to a speaker....

Could someone enlighten me on the whole phantom signal chain, and if there was any way my Mackie could have somehow fried their speakers??

Curiously,
:-) Rob
 
As far as I know, phantom power is only going to go down an XLR and they're having a lend of you, but I'm not the expert. Some of our more cleverer PA dudes should come along soon and give you a proper answer, so don't take my word for anything... that enough disclaimers?

Hard to see how it's possible to fry a speaker that has a PA amplifier in between it and your board which is connected to a send/out on their board... why didn't it fry both? The amp? Sounds dodgy to me...

In any case, they should know enough about their own equipment to not allow it to happen, even if it was possible. I mean, don't they recognise a condenser when they see one?
 
If you plugged into a quarter inch line input on your sub mixer there would not have been phantom present--this would only be provided on an XLR input. I don't know of any mixers that ever put phantom onto quarter inch jacks--and Mackie certainly don't.

If you had connected into an XLR, it could possibly have caused a problem, particularly with the various jack to XLR adaptors you mention which could result in some one-legged 48 volts being fed. I'd be sceptical of the problem occurring in a speaker rather than the mixer but I guess anything is possible.
 
If you were going into the Mackie on an XLR, you were sending phantom power to THEIR mixer. Not sure if the power would have passed thru the impedence transformer but I'm sure if it did, the damage would've been confined to their line out and shouldn't have blown a speaker.
 
Sounds As if they were just trying to fill up the outdoors or indoors with a small old peavey system.

This happens a lot!! I've seen it happen on numerous occations and had to work on other peoples old gear.

The problem and what everyone smelled was the circuit breaker fuse which happens to be an automotive dome light (believe or not!!!) looks kinda funny when you see that light bulb in there but they are in there.
The other possibility was that the In the speaker cabinet crossover failed and burnt. But they would have only lost the horns of the high end.

Either way there is noway possible that you, with far superior equipment, was in any way their down fall at this gig.
 
wouldn't you lose the phantom in the process of converting it to a 1/4 anyways?
 
Lt. Bob said:
wouldn't you lose the phantom in the process of converting it to a 1/4 anyways?
Click to expand...

If the conversion box used a transformer for proper impedance translation, then it would block the dc.
He said it was feed into a trs input on his side, so I can't imagine it had phantom power.
 
So was the signal hitting your mixer through an xlr or through a 1/4" input? The way I read it they had a 1/4" output going to your xlr input, correct?

There's like no real way that you would have messed up their speaker, even if your phantom power had jumped your 1/4" converter, there's no way it made it all the way to their speaker.
 
Lt. Bob said:
wouldn't you lose the phantom in the process of converting it to a 1/4 anyways?
Click to expand...

If you convert simply with a cable adaptor though, you'll get the full 48 volts. Phantom works by putting the DC voltage on pins 2 and 3 of the XLR and counts on the polarity inversion at the other end to cancel the voltage for gear that doesn't need it.

(Not saying that's what happened here, just that XLR to TS conversions and phantom don't mix.)

I once did accidentally feed phantom from a Yamaha board to a Soundcraft board when I ran out of inputs and needed a sub mixer. Nothing was fried but, while the phantom was on, I lost sound on the output and the meters went crazy. Luckily all was good as soon as I spotted my mistake.
 
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