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Destroyed my preamp by feeding phantom power into the output.
Old 21st November 2008
  #1
Gear Head
 

Destroyed my preamp by feeding phantom power into the output.

The title says it all really. I have (had) a presonus tubepre and hooked it up to my audio interface not realising the interface still had phantom power activated. The audio started making crackling noises but i didn't think anything was wrong as it's a real crappy, 3rd hand preamp which occasionally makes these sorts of noises anyway.
Then smoke started to rise from the vent.
It is now totally F##ked and doesnt respond to any mics anymore, i.e. the vu meter stays at 0% and no sound comes out.

Is it a write off? Is there anything i can do? Is it only dirt-cheap preamps with crappy wiring like this that get trashed by such a straightforward mistake?

I didn't really use it for aesthetic purposes, only needed it for phantom power (The phantom power on my interface is unreliable) and if i need to replace it i will probably just replace it with a power supply rather than a preamp. Anyone know if the behringer ps400 works ok?
Old 21st November 2008
  #2


I woulldn't expect p48 to blow out an output like that. The 6.8k feed resistors and conservative output design should survive a meeting like that.

Once you let the magic smoke escape, you can't expect it to work again unless you take it to a wizzard and have him put more smoke inside....



-tINY

Old 21st November 2008
  #3
Gear Addict
 
Nishmaster's Avatar
 

Phantom will blow outputs on cheaper devices where phantom protection diodes have been omitted due to cost or designer incompetence. You've probably blown some components here.

I would eschew the Behringer unit in favor of a Rolls phantom box.
Old 21st November 2008
  #4
Quote:
Originally Posted by tINY View Post

..schnipp......
Once you let the magic smoke escape, you can't expect it to work again unless you take it to a wizzard and have him put more smoke inside....



-tINY

If you open the lid, better close it quickly too. More might escape.
Old 21st November 2008
  #5
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Old Goat's Avatar
 

I have an ART Phantom III that works very well and wasn't too expensive. I also have a Berry that I bought in a fit of cheap-ass. That POS hums like a 70's Mazda with a Wankel engine!

Last edited by Old Goat; 21st November 2008 at 11:35 PM.. Reason: spell
Old 22nd November 2008
  #6
Gear Head
 

The rolls boxes look good but seem to be a bit scarce over here in the UK. If the Art boxes work ok then i'll probably get one of those. Thanks.
Old 22nd November 2008
  #7
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Unclenny's Avatar
Quote:
Originally Posted by Old Goat View Post
That POS hums like a 70's Mazda with a Wankel engine!
Had one of those.....RX2.

I let it sit for a while and the seals dried up. When I tried to start it it seized up faster than a Presonus TubePre under 48v Phantom power.
Old 22nd November 2008
  #8
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Old Goat's Avatar
 

Quote:
Originally Posted by Unclenny View Post
Had one of those.....RX2.

I let it sit for a while and the seals dried up. When I tried to start it it seized up faster than a Presonus TubePre under 48v Phantom power.

hehhehheh
Old 22nd November 2008
  #9
Quote:
Originally Posted by weownyoursoul View Post
The rolls boxes look good but seem to be a bit scarce over here in the UK. If the Art boxes work ok then i'll probably get one of those. Thanks.
don't know what interface you're using, but most have separate line and mic inputs (at the very least on a combi-jack. They SHOULDN'T ever feed phantom to the line input, and if you're coming out of a different preamp, the output's already going to be line level. So you shouldn't ever have had the issue, had it been hooked up correctly.
Old 22nd November 2008
  #10
Gear Addict
 

Quote:
Originally Posted by psycho_monkey View Post
don't know what interface you're using, but most have separate line and mic inputs (at the very least on a combi-jack. They SHOULDN'T ever feed phantom to the line input, and if you're coming out of a different preamp, the output's already going to be line level. So you shouldn't ever have had the issue, had it been hooked up correctly.
Exactemundo!
Old 23rd November 2008
  #11
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mdjice's Avatar
 

that s a great time to get a better Pre then !!
Old 25th November 2008
  #12
Gear Head
 

Quote:
Originally Posted by psycho_monkey View Post
don't know what interface you're using, but most have separate line and mic inputs (at the very least on a combi-jack. They SHOULDN'T ever feed phantom to the line input, and if you're coming out of a different preamp, the output's already going to be line level. So you shouldn't ever have had the issue, had it been hooked up correctly.
My interface (lexicon Lambda) has 2 xlr inputs and 2 1/4" inputs, one for each channel. As far as i know this is standard for most 2 channel interfaces. Therefore the xlr input, which i used to hook the 2 pieces of equipment together, was also the mic input.
I could have used the 1/4" input instead in which case the problem would not have occurred, but as on most cheapo preamps, the 1/4" output on the presonus is unbalanced and the xlr output is slightly hotter anyway so it's generally better to use the XLR output, which is why i did so.

"if you're coming out of a different preamp, the output's already going to be line level. So you shouldn't ever have had the issue"

You are correct if we assume that preamps don't colour the sound and would only be used for level boosting, rather than aesthetic reasons, but this, of course, is not true.

Besides, as i have already explained, the phantom power on my interface is unreliable and i largely only needed the preamp to provide a reliable power source which is why i am replacing it with a power supply, rather than another preamp.
Old 25th November 2008
  #13
Gear Nut
 
tubeydude's Avatar
 

This is a good reason to use TRS cabes from your external pres to interfaces of consoles... Most (all I believe) do not put phantom on the TRS conns.
Old 14th March 2011
  #14
Gear Head
 

How about an M-Audio Profire 610?

Could anyone tell me if an M-Audio Profire 610 would have any issues with phantom power being attached to one of it's outputs via a balanced cable?

Many thanks.
Old 14th March 2011
  #15
Quote:
Originally Posted by tomv-k View Post
Could anyone tell me if an M-Audio Profire 610 would have any issues with phantom power being attached to one of it's outputs via a balanced cable?

Many thanks.
why is it even an issue? why are you running preamp output into mic input?
Old 14th March 2011
  #16
Gear Head
 

I mean going out of the profire line output into a mic input.

In a live situation, it is my loose understanding that a DI box is unneccesary if you can provide the FOH with a balanced signal which can be attentuated, but if they are used to powering active DI boxes there could be a chance that phantom power gets sent to the interface?
Old 14th March 2011
  #17
Quote:
Originally Posted by tomv-k View Post
I mean going out of the profire line output into a mic input.

In a live situation, it is my loose understanding that a DI box is unneccesary if you can provide the FOH with a balanced signal which can be attentuated, but if they are used to powering active DI boxes there could be a chance that phantom power gets sent to the interface?
I know what you mean.

why would you go out of a line output into a mic input? go out of a line output into a line input!

Line inputs can be balanced too. No sensibly designed desk would send phantom to a line input.

and there's ALWAYS a chance for things to go wrong - it's called pilot error.
Old 14th March 2011
  #18
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by tomv-k View Post
I mean going out of the profire line output into a mic input.

In a live situation, it is my loose understanding that a DI box is unneccesary if you can provide the FOH with a balanced signal which can be attentuated, but if they are used to powering active DI boxes there could be a chance that phantom power gets sent to the interface?
Live Or studio a DI box is used going into a mic pre..
Old 14th March 2011
  #19
Quote:
Originally Posted by nosebleedaudio View Post
Live Or studio a DI box is used going into a mic pre..
that's not what he's asking though...I think he's thinking that XLRs are mic input only, and you can only send a balanced signal to a mic input.
Old 14th March 2011
  #20
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davet's Avatar
 

Quote:
Originally Posted by tINY View Post

I woulldn't expect p48 to blow out an output like that. The 6.8k feed resistors and conservative output design should survive a meeting like that.

Once you let the magic smoke escape, you can't expect it to work again unless you take it to a wizzard and have him put more smoke inside....



-tINY
LOL! from Eugene Tiny.
Old 14th March 2011
  #21
Gear Nut
 

Quote "I could have used the 1/4" input instead in which case the problem would not have occurred, but as on most cheapo preamps, the 1/4" output on the presonus is unbalanced and the xlr output is slightly hotter anyway so it's generally better to use the XLR output, which is why i did so."

Regardless, you fed a mic preamp(line level) into a mic preamp. Even if you hadnt fried the first preamp, you still would have been degrading the sound quality of your signal. And I'm assuming the distance from pre to interface wasnt too long, so was a balanced connection 100% necessary?

Just sayin.
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