Phantom power question

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rkmase

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So I've got a new Soundcraft Compact 4 mixer, which provides two of those XLR/TRS combo inputs. Now, the Phantom power button sends the current to both inputs.

Now, is Phantom power only sent through XLR sockets, or will it be sent through a 1/4 input (non-balanced) instrument cable if its plugged in there as well? The manual does mention not using unbalanced XLR inputs if you happen to have a dynamic mic plugged in, but nothing about 1/4 or TRS inputs.

Basically, I want to record an acoustic/electric guitar with a mic and DI simultaneously.

I just dont want to fry anything.
 
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rkmase said:
So I've got a new Soundcraft Compact 4 mixer, which provides two of those XLR/TRS combo inputs. Now, the Phantom power button sends the current to both inputs.

Now, is Phantom power only sent through XLR sockets, or will it be sent through a 1/4 input (non-balanced) instrument cable if its plugged in there as well? The manual does mention not using unbalanced XLR inputs if you happen to have a dynamic mic plugged in, but nothing about 1/4 or TRS inputs.

Basically, I want to record an acoustic/electric guitar with a mic and DI simultaneously.

I just dont want to fry anything.
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Phantom power will only go to the XLR inputs, and it's for condensor mics, which require power to work properly.
 
Awesome. All I needed to know. Those combo-inputs threw me.
 
I dont know about soundcraft, but on most other mixers... if you plug a 1/4 non balanced cable into the line in jack... with phantom power on.... smoke comes out of the mixer and the phantom power is dead!!!!
 
JCM900 said:
I dont know about soundcraft, but on most other mixers... if you plug a 1/4 non balanced cable into the line in jack... with phantom power on.... smoke comes out of the mixer and the phantom power is dead!!!!
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that would be interesting...if it were true

As you can see in the attached picture of a popular Mackie mixer, the phantom power is after the XLR inputs...the 1/4" inputs take a differet path past the phantom power.
 

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And I suppose I could have answered my own question by using some common sense and looking at the schematic :p But yeah, looks like its separated from the trs/ 1/4 input and comes in before.
 

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I guess you cant read schematics at all then... take a look... the phantom power in both instances feeds both the line in and the XLR... they are parallel.
If you dont believe me... plug a non balanced 1/4" plug into the line out, with the phantom power on...and see what happens :)
 
I should have mentioned before... on the phantom power.... there are no diodes between the XLR and the line in jacks to isolate them, except the one noted as guitar/mono, and it has the hi/z switch to disable the phantom power , and the voltage from the phantom power goes BOTH ways.
 
JCM900 said:
I guess you cant read schematics at all then... take a look... the phantom power in both instances feeds both the line in and the XLR... they are parallel.
If you dont believe me... plug a non balanced 1/4" plug into the line out, with the phantom power on...and see what happens :)
Click to expand...

Uhh...those little double vertical lines on the wires inbetween the XLR and 1/4" inputs are the symbols for capacitors in schematics. Capacitors block DC like phantom power. In fact, those are specifically called blocking capacitors, because they are there to stop phantom power from hitting the 1/4" input.

If that happened to you, there was something wrong with the mixer.
 
JCM900 said:
If you dont believe me... plug a non balanced 1/4" plug into the line out, with the phantom power on...and see what happens :)
Click to expand...

did it. and it's still sitting plugged in while I sit here....nothing is happening. Preamp still works fine too.

like boingoman said, manufacturer's build mixers the way they do to help avoid this problem. Don't you think you'd see some sort of warning in the manual of the mixer if phantom power actually harmed unbalanced gear?
Not to mention the mixer is going to contain current limiting resistors. So if the microphone or cable is wired wrong, these resistors are going to restrict flow to the mic.
 
JCM900 said:
I dont know about soundcraft, but on most other mixers... if you plug a 1/4 non balanced cable into the line in jack... with phantom power on.... smoke comes out of the mixer and the phantom power is dead!!!!
Click to expand...

If so, the mixer is either defective or designed by complete idiots. Not that I don't believe it has happened to you, but if it has, your mixer was designed or built incorrectly to begin with.
 
I concede. It wasnt that it happened to me, I mis-read the manual, and they all say the same thing, dont use unbalanced MIC cables on the MIC inputs while phantom power is on. I looked on mackies site at their manuals, and they say the same thing. So anyway, Rock on dudes!
I am a happier human being today, for I have learned something.
 
It really comes down to how thos combo jacks work. On his mixer, there is no separate jack for the line input.

I just looked on the neutrik site, it doesn't look like there is a way to connect the 1/4 separately from the xlr.

I would call Soundcraft.
 
Farview said:
It really comes down to how thos combo jacks work. On his mixer, there is no separate jack for the line input.
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nah, the combo jack separates the XLR from the TRS/TS still....they touch different contact points.
The schematics for his unit look basically the same as the Mackie one I gave above (except they allow Hi-Z input on channel 2).
 

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bennychico11 said:
nah, the combo jack separates the XLR from the TRS/TS still....they touch different contact points.
The schematics for his unit look basically the same as the Mackie one I gave above (except they allow Hi-Z input on channel 2).
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Are you sure? That one has 6 contacts because it is a switching jack. The other 3 are the thru.
 
Farview said:
Are you sure? That one has 6 contacts because it is a switching jack. The other 3 are the thru.
Click to expand...

well, here's the Compact 4's schematic
They have to go to two different contact points...they're two different signals. If they're going to be passed thru the same amplifier, the line level signal is going to have to be padded. Yeah?
 

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Just making sure, All the stuff I have with the combo jacks only has 3 connections and the Neutrik site didn't seem to address it.
 
Farview said:
Just making sure, All the stuff I have with the combo jacks only has 3 connections and the Neutrik site didn't seem to address it.
Click to expand...

hmmm, is there a switch for 'em?
and is this on a mixer or a device that only accepts line level?
 
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