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XLR Hiss (Phantom Power and Helix)

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Excuse the resurrection. If I were to briefly switch on phantom power of a mic preamp whilst the Helix (floorboard) XLR outputs are already connected to it, would there still be damage? Is the end result a dead output, a dead Helix, or permanent poor sound quality, even after phantom power was turned off?

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Excuse the resurrection. If I were to briefly switch on phantom power of a mic preamp whilst the Helix (floorboard) XLR outputs are already connected to it, would there still be damage? Is the end result a dead output, a dead Helix, or permanent poor sound quality, even after phantom power was turned off?

There's no risk of damage to the Helix from phantom power.

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There's no risk of damage to the Helix from phantom power.

It just won't sound as good.

 

DI, Phil's quote is worthy of being a suggested use Tip in the next version of the Helix User Manual, so users are not otherwise concerned about damaging their Helix.

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It just won't sound as good.

 

DI, Phil's quote is worthy of being a suggested use Tip in the next version of the Helix User Manual, so users are not otherwise concerned about damaging their Helix.

 

Also, this whole thread is a very good suggestion for the upcoming Line 6 products ;)

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It just won't sound as good.

 

DI, Phil's quote is worthy of being a suggested use Tip in the next version of the Helix User Manual, so users are not otherwise concerned about damaging their Helix.

Yes, because there were some other threads talking about the need for a DI box to protect the Helix from this very same thing. If there is only risk of a bad sound and no hardware damage, then the DI box is not necessary. 

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It's interesting that with my Helix, on every board I've tried it on with phantom power being on, I never get a hiss as long as I have the ground lift on. I do, however, get quite a large amount of attenuation. I would bet it's about 12dB or so.

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Question. Are there still a lot of mixers out there that don't have individual phantom power switches? I realize that most small (8 channels or less) mixer would understandably have a global phantom power switch but I seem to remember that even my small Allen & Heath mixer had individual phantom power switches per channel. The last 16 channel board I used that didn't was the very old Mackie 1604.

 

My mistake. Just looked up that mixer. Global phantom power.

 

Still even if your band is just a three piece, wouldn't you be using a bigger board anyway just for the extra controls and options that often aren't in the smaller boards?

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Question. Are there still a lot of mixers out there that don't have individual phantom power switches? I realize that most small (8 channels or less) mixer would understandably have a global phantom power switch but I seem to remember that even my small Allen & Heath mixer had individual phantom power switches per channel. The last 16 channel board I used that didn't was the very old Mackie 1604.

 

Yes, this question comes up a lot around this Helix issue... I don't know the answer in general but Line 6 M20d mixer reportedly doesn't have per channel switches.

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Yes, this question comes up a lot around this Helix issue... I don't know the answer in general but Line 6 M20d mixer reportedly doesn't have per channel switches.

Unless it's a small mixer, that just seems silly in this day and age.

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Unless it's a small mixer, that just seems silly in this day and age.

 

I don't know much about it but it seems to have 12 XLR/TRS combo ins plus some more inputs (probably 20 channels altogether). But I think that what's silly in this day and age is that Helix cannot really tolerate phantom power on its XLR outs. For such a wonderful piece of technology it seems really ridiculous. The inability of M20d to work together with Helix is just completing the joke. I'm a huge fan of Line 6 and Helix in particular but Line 6's inability to explicitly admit they've dropped the ball here is really... hurting my feelings :)

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I don't know much about it but it seems to have 12 XLR/TRS combo ins plus some more inputs (probably 20 channels altogether). But I think that what's silly in this day and age is that Helix cannot really tolerate phantom power on its XLR outs. For such a wonderful piece of technology it seems really ridiculous. The inability of M20d to work together with Helix is just completing the joke. I'm a huge fan of Line 6 and Helix in particular but Line 6's inability to explicitly admit they've dropped the ball here is really... hurting my feelings :)

Agreed. It is indeed a two-sided issue. I do find it interesting that some phantom power systems are better (less noisy) than others. I have used mixers that produce more hiss with the phantom power turned on - even with nothing connected. Technically speaking, phantom power is supposed to be "invisible" to devices that don't need it. Yet, here we are.

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I don't know much about it but it seems to have 12 XLR/TRS combo ins plus some more inputs (probably 20 channels altogether). But I think that what's silly in this day and age is that Helix cannot really tolerate phantom power on its XLR outs. For such a wonderful piece of technology it seems really ridiculous. The inability of M20d to work together with Helix is just completing the joke. I'm a huge fan of Line 6 and Helix in particular but Line 6's inability to explicitly admit they've dropped the ball here is really... hurting my feelings :)

 

I've not had it confirmed, but I'd be willing to bet the issue has to do with the auto-sensing feature on the Helix XLR outs that allows automatic summing to mono if only one XLR is used. No other Line 6 device has had this on its XLR outputs, and no other Line 6 device has had issues with phantom power.

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Question. Are there still a lot of mixers out there that don't have individual phantom power switches?...

 

 

Might not be the point. Because user error is more of a factor in these scenarios than we want to admit, and also, imho, running 1/4" to a DI to XLR also avoids the possibility that level from Helix isn't just what the mixer wants, so I just use that. Every time. It sounds the same.

 

XLR connections? I'd use them in the studio and in an entirely controlled environment. As soon as you have another person who can muck it up... give me the DI box every time.

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I've not had it confirmed, but I'd be willing to bet the issue has to do with the auto-sensing feature on the Helix XLR outs that allows automatic summing to mono if only one XLR is used. No other Line 6 device has had this on its XLR outputs, and no other Line 6 device has had issues with phantom power.

If this reasonable assumption is indeed correct, it sure would be nice for Line 6 to include a sentence or two mentioning it in the Helix User Manual. They could depict the auto-sensing feature as a benficial aspect, and offer the reassuring Tip that Phantom Power will not damage the Helix (just possibly degrade or attenuate the sound, and the suggestions that enabling the Ground Lift may help, and a DI or in-line XLR Phantom Power filter be used, if Phantom Power is present.

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I'd love to see something in the manual or data sheet from Line 6 that specifies the output sufficiently to determine if phantom power is simply just a mere hiss causing annoyance, or if the Helix may be damaged by it (or possibly cause damage). Who knows why there is hiss, I can think of a dozen circuit possibilities that could explain it that it's not even worth speculating. Lifting the ground may help, but only if there is no alternative low impedance ground path between the two pieces of equipment - if there is, then you're back where you started when it comes to phantom power causing problems.

 

Making a low impedance non-transformer based output safe for phantom power needs heavy protection diodes, enormous voltage headroom or a higher output impedance to limit current inrush. Many of these methods affect the signal to noise/distortion ratio of the output, especially for longer cable runs. We know the Helix XLRs are not transformer coupled, which means it may be susceptible to being plugged into phantom power. Heavy protection diodes moves the risk across to the input side (yes, the side that is supplying the phantom power can be damaged too).

 

When an input that has phantom power enabled is suddenly plugged into a device that is not designed to be powered by phantom power, there is a sudden inrush of current through protection diodes at both ends while the output coupling caps charge up. The moment the devices are plugged together, the 48V is applied and charges up the output stage coupling caps with a high surge current through the protection diodes of the output and input stages. If either the output or input is not current limited, or both ends don't have high rated protection diodes (ie. not the ones built into the input/output op-amps), then something is likely to be degraded/damaged and at some point fail. I have no idea what the Helix output circuit looks like, so I can't make a call. But, if it is protected with huge protection diode clamps, there is still a risk of damaging the input stage of the mixer/desk. This is why manuals always warn that phantom power must only be switched on after everything has been plugged in. Plugging in devices before enabling phantom power limits the charge current to the phantom power bias resistors (which is less than 10 milliamps).

 

Even ignoring the inrush surge currents, if a device has a capacitively coupled output, the caps need to be rated sufficiently (and polarised appropriately if they are polarised capacitors) to avoid being damaged by the existence of phantom voltages - even if very little or no current is flowing. Again, with no specs or official statements from Line6, I wouldn't make a call that its outputs won't be degraded, and at some point fail.

 

As PeterHamm says, its always safe to use a DI box. That way you don't have to second guess yourself, and you get all the advantages of a DI box including attenuation, total galvanic isolation with transformer based models, and whatever your box supports. Over the years, I've seen many mixer inputs die and random gear stop outputting on one or more channels, almost definitely due to the stresses of using phantom power where it is not supposed to be used. Maybe the Helix is ok, but why risk it.

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M20d allows Phantom to be enabled/disabled for XLR inputs 1-6 and 7-12 independently.

 

I only enable phantom for the drum overhead mics and the other channels in that group are always dynamic mics (kick, snare, vox).

 

All of the direct inputs - Helix, Bass DI, Guitar/Mando DI, Keys come through the other group of inputs

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