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Phantom power Helix LT


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Hello Forum members,


I've recently bought a Helix LT and very happy with it so far. The way I use it (for now) is that in live situations (rehearsal, we don't gig yet) I have patches set up with two signal paths.

The effects only go to the 1/4" out which feed into the the front of the tube-amp we have in our rehearsal room.

At home I don't have an external amp, so the effects + amp + cab simulation go to the XLR and I play using headphones. Maybe not ideal, but it does the job and allows  me to set up patches quickly. 


But what I want to do next is to feed the XLR to the mixing desk in the rehearsal room so as to have both the amp as well as a signal for mixing. This mixing desk may have phantom power turned on (although usually off) and as multiple bands use the same rehearsal room I don't want to risk feeding phantom power to my Helix.


I have browsed through the forums and found a lot of valuable information; an often used method is to go from the 1/4" to a DI box.

But what I want to do is to use the XLR out (at mic level) and feed that to the mixing desk.


I have purchased an "ART DTI"  transformer/ isolator as I found some people recommending that device. My understanding is that compared to a DI box it leaves the signal level intact (i.e. MIC in = MIC out). Other than that it works pretty much the same as a DI box (but I do not know that for sure..... I don't know too much about electronics)


All this said, I am confused about the following and hope someone could give me a clear answer on this:


1) Does this ART DTI indeed prevent the phantom power from going to the XLR outputs of the Helix?

2) I noted that when turning phantom power on there is a " plop"  in the signal (I did some experimenting at home using my Focusrite soundcard; my headphones were connected to the soundcard). If I disconnect the Helix but leave the ART DTI still connected this "plop"  is hardly noticeable. Does this still mean that even when the DTI is connected some signal is being sent to the Helix?

3) What actually happens when the Helix is exposed to phantom power? Will the electronics be damaged? I know that Line 6 clearly states not to use  phantom power, but it is unclear at least what might actually happen, i.e. what the risk is.

4) What is actually the difference between dedicated " phantom power blockers" and the ART DTI isolator/transformer.


Please don't suggest me to do things differently. I'm quite aware of what the Helix can do in terms of routing and indeed there may better ways to do what I want to achieve. I'm just trying to understand how this phantom power issue works and whether the additional product I bought actually protects me or not.


Thanks a lot !!!
















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1. Yes, it prevents. Art DTI is passive, transformer based. Albeit it is step down 3:1 transformer. You connect high impedance unbalanced, line level signal to get low impedance 9dB lower "mic level" balanced signal.
2. Don't bother.
3. Nothing happens. Line 6 clearly states that no damage happens when phantom is applied. The manual is more restricted.
4. It depends on the design. If "phantom blocker" is transformer based, it should be no step down.

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Thanks !!!


On the box of the ART it says "1:1 unity gain", so not sure if indeed it is step down.

What I do is Helix (XLR out) to ART (XLR in) and then ART (XLR out) to Mixer (XLR in). No unbalanced signals as far as I understand.



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Actually it is not DI box, it is isolator. You can use it when you have issues with built-in DI box or you want transformer sound. You can also connect it with TRS 1/4" outputs. They are impedance balanced. Do whatever makes sense to you.


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Thanks again!


Indeed I know it is not a DI box and this is actually what caused the confusion. The way I understood this product is that it can do (at least) 3 things:

- shield my Helix from phantom power (which you confirmed) while using only XLR connections and (hence) balanced cables

- eliminate hum (which is not the case right now, but who knows when I might need it for that purpose)

- to go from any one of 1/4", RCA or XLR to another (or the same) output (whether line or mic level; not sure how much I'd need that, but it's a nice option)


What I'm still not fully sure about is whether an unbalanced input (1/4"or RCA) will be "transformed" (not sure it is the right word) to a balanced (XLR) output.

A DI box would (as I understand) transform an unbalanced line level to a balanced mic level. But I already set my XLR to "mic" level, so there's no need for such transformation; moreover I want (for now) to use the 1/4" out for other purposes.


Will move on now to making music (which is a much bigger challenge and not dependent on too much technology :-))

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