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Will phantom power damage or disrupt a DI'd instrument?

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Will phantom power damage or disrupt a DI'd instrument?

Postby Rocknrollerlondon » Tue Jun 01, 2010 7:16 pm

Hello,

Will phantom power damage or disrupt a DI'd instrument such as a bass, guitar, or synth? I'm using a passive DI box.

Thanks
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby ef37a » Tue Jun 01, 2010 7:42 pm

What in the name of Ohm are you doing that could possibly put Ppower on those devices?

The short answer is no to the bass and guitar if they are passives but the output chip of a synth might not take kindly to 48 volts up its jaxi! Very much depends upon how that output stage is configured.

One of the biggest dangers of phantom power is the huge crack or pulse it can send thru' power amps and speakers if shorted, the short itself will cause the mixer or preamp P power circuits no harm at all!

But do give us some more details please!

Dave.
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Rocknrollerlondon » Tue Jun 01, 2010 7:51 pm

Thanks Dave,

My 8 channel interface has global phantom power, 1-4 and 5-8.

If I had the option then I wouldn't turn on the phantom power to a DI'd bass.

I thought it would be harmless because if you were using an active DI, which would most likely use phantom power, then that wouldn't harm the instruments??
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby ef37a » Tue Jun 01, 2010 8:06 pm

"My 8 channel interface has global phantom power, 1-4 and 5-8."

WHICH 8channel interface? (! like drawing TEETH sometimes!)

IF you are using any kind of DI box into a mic input with spook juice on it it is NEVER going to get to the instrument.

If the AI has dedicated DI inputs there will not be +48 on them..or if there is the designers should be shot!

BUT, alway turn gains and faders to minimum when switching phantom power on or off for the sake of ears, amps and speakers.

Dave.
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby ewe » Tue Jun 01, 2010 8:12 pm

Phantom Power should not be reaching the instrument that is plugged into your DI box unless there is something wrong with it! Check the instruction manual for the DI though just to make sure it is designed to deal with phantom power (It would be strange if it wasn't).
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Rocknrollerlondon » Tue Jun 01, 2010 8:33 pm

Dave, I have an M-Audio Fast Track Ultra 8R.

Ewe, thanks for that.

If a DI box does not pass on the phantom power to the instrument then that is all I need to know.

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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby ef37a » Tue Jun 01, 2010 8:40 pm

Ah! And I have its grandad the fast track pro,most handy.

You will be fine with that ultra.

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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Bob Bickerton » Tue Jun 01, 2010 8:42 pm

I think the question should have read "is it OK to run phantom power into a passive DI box" answer "Yes".

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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby ef37a » Tue Jun 01, 2010 8:47 pm

In fact Bob the question should have been..

Will the phantom power on the MIC inputs of my FAST TRACK ULTRA have any impact upon anything plugged into the DI input of same?

Answer no.

But we got there anyway!

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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Rocknrollerlondon » Tue Jun 01, 2010 8:55 pm

Thanks for the reply's.

Next time I'll put more thought into the wording of my question
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Hugh Robjohns » Wed Jun 02, 2010 12:20 am

One of the requirements of a DI box (whether active or passive) is to be able to provide galvanic isolation of the instrument from whatever is connected to the output of the DI box.

All passive DI boxes and pretty much every active DI box I've come across use a transformer to provide that galvanic isolation.

The one thing a transformer can't do is pass DC volts, so you can rest easy in the knowledge that if you connect a DI box to a mic input with phantom power turned on, none of that power will find its way through to the instrument connected to the DI input.

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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Rocknrollerlondon » Wed Jun 02, 2010 12:37 pm

Thanks Hugh. I'm probably being too over cautious.

I've never damaged or had issues with my own equipment or instruments. I'm recording a rehearsal for a band and it's the first time I'm using all of my gear in this way. I know they have some expensive kit so I though it would be best to get some assurance.
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Bob Bickerton » Wed Jun 02, 2010 10:44 pm

ef37a wrote:In fact Bob the question should have been..

Will the phantom power on the MIC inputs of my FAST TRACK ULTRA have any impact upon anything plugged into the DI input of same?

Answer no.

But we got there anyway!

Dave.

Bit pedantic Dave, it's pretty obvious that the phantom power will be from the mic inputs, and the make and model of the source of 48v is unlikely to have any influence on the outcome of the question ....... but now I'm being pedantic

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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby ef37a » Wed Jun 02, 2010 11:03 pm

Pedantic we may be Bob but how can anyone answer questions unless we know the hardware we are dealing with?


"How do I bias the valves in my amp?" is an example!

G'night all,
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Re: Will phantom power damage or disrupt a DI'd instrument?

Postby Hugh Robjohns » Thu Jun 03, 2010 12:18 pm

Er... if we're all wearing our 'Mr Pedantic' hats, it was not necessary to know about the interface. The original question stated very clearly that the OP was using a passive DI box.

All passive DI boxes contain a transformer. Transformers do not pass DC. All is safe.

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