Blocking Phantom Power

[npulsipher]

Ok, I did do a search on this but I am an electronics noob so it was all complete gibberish to me.

I do a lot of remote gigs, and I'm cheap and didn't want to pay $200 for a bag with some rack rails in it, so I made my own. The only thing I have left to do is build a short snake to get the inputs on the back of my gear to the outside of the bag.

They're combo connectors, but my plan is to just build an XLR snake, and use something like this NA3MJ - Neutrik on the end of it if I need a line input.

My question is will this let phantom power through? If so is there a way to build something like that with a cap in it to block the phantom power (so I don't accidentally fry something).

Thanks!

[henryf]

Originally Posted by npulsipher

My question is will this let phantom power through?

It looks to me like it will.

Originally Posted by npulsipher

If so is there a way to build something like that with a cap in it to block the phantom power (so I don't accidentally fry something).

You could come up with a circuit that blocks steady-state phantom power using capacitors in series with the phantom power lines. And, the right diodes on the far side of the caps could add some protection from transient voltage spikes. But, mechanically packaging it so it looks like that commercial adapter is going to be difficult. Packaging the circuit in a project box a little larger than necessary -- like a DI box -- would be easier.

[wwittman]

Originally Posted by npulsipher

Ok, I did do a search on this but I am an electronics noob so it was all complete gibberish to me.

I do a lot of remote gigs, and I'm cheap and didn't want to pay $200 for a bag with some rack rails in it, so I made my own. The only thing I have left to do is build a short snake to get the inputs on the back of my gear to the outside of the bag.

They're combo connectors, but my plan is to just build an XLR snake, and use something like this NA3MJ - Neutrik on the end of it if I need a line input.

My question is will this let phantom power through? If so is there a way to build something like that with a cap in it to block the phantom power (so I don't accidentally fry something).

Thanks!

why would you "accidentally fry something"?

if you plug in XLR mics to XLR inputs, all 3 pins go in together and phantom is perfectly "safe" unless a mic is mis-wired.
better to spend your electronics acumen on ensuring all your mics are wired correctly... and then forgetting all about phantom

hundreds of the world's greatest studios have (or had) phantom on all the time on their consoles... plugging in every type of mic day in and out.
it's simply not a worry.

[henryf]

The circuitry I mentioned previously was just to prevent the phantom power from getting through to your line-level equipment. I think you'll also want to build in a balanced attenuator -- typically three resistors -- to lower the line level signal to mic level.

[npulsipher]

Originally Posted by henryf

The circuitry I mentioned previously was just to prevent the phantom power from getting through to your line-level equipment. I think you'll also want to build in a balanced attenuator -- typically three resistors -- to lower the line level signal to mic level.

henryf is correct. My concern is for when I plug in something like a keyboard. I don't want to have a brain fart and accidentally push the phantom power button on the wrong channel and send 48v down the line to an instrument.

henryf - I have a pad built into inputs that I'm trying to reach, do I still need to need to build in an attenuator?

Thanks again for your input.

[mjrippe]

Originally Posted by npulsipher

henryf is correct. My concern is for when I plug in something like a keyboard. I don't want to have a brain fart and accidentally push the phantom power button on the wrong channel and send 48v down the line to an instrument.

Not to mention that if you plug in a 1/4" TS (unbalanced) instrument plug you would be shorting +48 to ground...

[npulsipher]

Or would it be easier to just buy a cheap DI box like this: Behringer Ultra-DI DI20 | Sweetwater.com

[henryf]

Originally Posted by npulsipher

Or would it be easier to just buy a cheap DI box like this: Behringer Ultra-DI DI20 | Sweetwater.com

FWIW, I read on the Behringer site that if you hold off buying their products until February, the limited warranty will be extended to 3 years.

[npulsipher]

Sounds good to me! Thanks for your help!

[Matt Syson]

Hi
A pad is an attenuator, just a different name.
Fitting capacitors in series with the signals would stop the phantom. If you can solder neatly it would be easy enough to put it together.
Matt S