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The 'Phantom' of the Phantom Power Light!
Old 10th November 2016
  #1
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timtoonz's Avatar
The 'Phantom' of the Phantom Power Light!

Techie question for y'all...

I've got an API 512c pre in one of my lunchboxes. The input is connected to a KM84 (on snare, of course), and the output goes to an API-550a EQ next to it in the rack.

Every now and again I notice the phantom power light on the API-512 glowing for a second or so, then fading back to blackness. All while the rack is powered OFF.

Is this in any way 'normal'? Or does it indicate some sort of problem with either the pre, the cable, or the microphone?

OR is there simply a ghost in my lunchbox?

Old 11th November 2016
  #2
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timtoonz's Avatar
Huh. Nobody even has a theory? Interesting....

Old 11th November 2016
  #3
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iangomes's Avatar
Doesn't sound good... haven't seen that issue before.
Old 11th November 2016
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Is this right after power down? Say a couple of seconds?
One thing is, the Lunch box does not have a bleeder on the Phantom, something I add to the Mods I perform..
Old 12th November 2016
  #5
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Quote:
Originally Posted by nosebleedaudio View Post
Is this right after power down? Say a couple of seconds?
One thing is, the Lunch box does not have a bleeder on the Phantom, something I add to the Mods I perform..
Nope. The whole thing's been powered off for hours, and I'll just be sitting there working when I notice it out of the corner of my eye. Just every now and again, the 512's phantom light comes on and then fades away again.

The whole lunchbox (an OSA 8-Space) is plugged into a power bar that's turned off. So my theory is that maybe some how a small charge comes from the mic down the cable to the pre? Could it be a prob with the KM84? But that doesn't make sense since the mic gets its power FROM the pre, so... yeah. Just doesn't make any sense!

Old 12th November 2016
  #6
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Quote:
Originally Posted by timtoonz View Post
Nope. The whole thing's been powered off for hours, and I'll just be sitting there working when I notice it out of the corner of my eye. Just every now and again, the 512's phantom light comes on and then fades away again.

The whole lunchbox (an OSA 8-Space) is plugged into a power bar that's turned off. So my theory is that maybe some how a small charge comes from the mic down the cable to the pre? Could it be a prob with the KM84? But that doesn't make sense since the mic gets its power FROM the pre, so... yeah. Just doesn't make any sense!

Its not the mic or pre, its the OSA..
Old 12th November 2016
  #7
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Quote:
Originally Posted by nosebleedaudio View Post
Its not the mic or pre, its the OSA..
Yeah I suspect you could be right. But how is it even possible when the power to the lunchbox is switched off?

Mind you - I used to have problems with the OSA's phantom power, which resulted in one of my mics (a phantom powered Gefell UM900) giving off a weird hiss. So I had a tech I trust fix the OSA's power supply, and my phantom power-level problems went away.

BUT given that the phantom section of the power supply was a) troubled to begin with, and then b) modified, maybe theres' still something screwy going on.

I just watched the pre closely and it seems like it does the 'phantom flash' almost once every minute. It's as if a certain amount of charge builds up until the light flashes, and then it resets and starts again...

I'm just curious how such a thing is possible while turned off. Maybe I should disconnect the power plug from the wall and see if it continues to happen.
Old 12th November 2016
  #8
Do you have it plugged into a power conditioner or is it straight to the wall?
Old 12th November 2016
  #9
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iangomes's Avatar
Are you feeding it phantom from somewhere else, accidentally? Maybe through a normal ifnit isn't obvious?
Old 12th November 2016
  #10
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by timtoonz View Post
Yeah I suspect you could be right. But how is it even possible when the power to the lunchbox is switched off?

Mind you - I used to have problems with the OSA's phantom power, which resulted in one of my mics (a phantom powered Gefell UM900) giving off a weird hiss. So I had a tech I trust fix the OSA's power supply, and my phantom power-level problems went away.

BUT given that the phantom section of the power supply was a) troubled to begin with, and then b) modified, maybe theres' still something screwy going on.

I just watched the pre closely and it seems like it does the 'phantom flash' almost once every minute. It's as if a certain amount of charge builds up until the light flashes, and then it resets and starts again...

I'm just curious how such a thing is possible while turned off. Maybe I should disconnect the power plug from the wall and see if it continues to happen.
Unplug it completely...then see...
Old 13th November 2016
  #11
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Originally Posted by vsthalion View Post
Do you have it plugged into a power conditioner or is it straight to the wall?
It's plugged into a power conditioner...

I tried unplugging it completely and the flashing seems to have stopped. So if I'm guessing, it seems like even when it's turned off, it's somehow drawing tiny bits of power and perhaps that builds up over time until it's enough to turn the power light on, then it discharges and the cycle starts again...

Just a theory but the bottom line is that either a) I need to get that power supply fixed again, or b) I give up on the OSA and get another BAE or similar (I have a 10 space BAE lunchbox that sits under my OSA one).

The Phantom of the Phantom Power has struck at my pocket book once again!
Old 15th November 2016
  #12
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emrr's Avatar
The OSA lunch box has no power components present, and as a side note it's pin-out does not follow the VPR standard in several ways. I documented this differences over at GroupDIY while converting one I have. The PSU that came with seems to have varied widely in method and construction, no telling.
Old 18th November 2016
  #13
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Quote:
Originally Posted by emrr View Post
The OSA lunch box has no power components present, and as a side note it's pin-out does not follow the VPR standard in several ways. I documented this differences over at GroupDIY while converting one I have. The PSU that came with seems to have varied widely in method and construction, no telling.
Thanks for the info - very interesting.

At least I was able to verify that the phantom-light doesn't come on when the unit is completely unplugged. So that means a small amount of power must somehow be filtering into the lunchbox even when the power supply is switched off.

Kinda bizarre... But now I have to decide if it's enough of a problem to justify the expense of a new lunchbox. Either that or another trip to the tech... which would at least be cheaper.

Thanks all for your input.
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