How do I use Radial Pro D2 to protect my mixer?

[alexis]

Hi -

I am running two TRS lines to a Soundcraft UI24r from my Mackie ProFX12v3+ personal mixer, both at line level: one is the mono output originating from my keys, and another is the vocal. The Soundcraft UI24r feeds the FOH PA.

I've learned (from Hugh!) that if phantom power is inadvertently enabled at the Soundcraft UI24r channels my cables happen to be plugged into, my Mackie mixer could get fried, and the best thing for me to do prophylactically is to use a DI box. I know phantom power can be applied to the Soundcraft UI24r XLRs, and in an overabundance of caution I'm also assuming it can also inadvertently be applied to the TRS inputs as well (is that incorrect?). I should note I'm not in charge of the Soundcraft, but even if I were I wouldn't trust myself to not make a mistake.

I have one new Radial Pro D2 box, and after looking it over and reading the information available, I'm not quite sure how to use it

Can someone give me some guidance please?
1. Would I need two Radial Pro D2 boxes, one for the keys, and one for the vox (or can one box be used for both)?
2. Clearly I need to engage the "Ground Lift" button(s) if I want to protect against phantom power running from the Soundcraft UI24r back into my Mackie ... right?
3. Are outputs of the Radial Pro D2 "THRU" and "XLR" still at line levels after the "Ground Lift" button is engaged?
4. Should I use the "THRU" ports or the "XLR" ports to route signals from the Radial Pro D2 to the Soundcraft UI24r? I'm guessing the "XLR" ports, since that's where the "Ground Lift" button is physically located ... ?
5. Do I actually not have to worry about phantom power inadvertently being applied to TRS lines running from my Mackie mixer in to the Soundcraft UI24r ... or is phantom power only able to be applied at XLR inputs on the Soundcraft?
6. I think I've read (but can't find that again to confirm, so maybe I just misunderstood) that ground lifting can affect the actual tone of the signal coming out of the Radial Pro D2 - is that a thing, and should I be concerned, or is it only hypothetical?

Sorry for so many questions ... I am so inexperienced here, in my last band I think we just all "plugged in" and didn't worry about anything, ignorance was bliss!

Thank you!

[Hugh Robjohns]

I have one new Radial Pro D2 box, and after looking it over and reading the information available, I'm not quite sure how to use it

It's a passive, two-channel DI box. You can use it for a single stereo source, or two mono sources... which is handy as you have two mono sources — keys and voice.

1. Would I need two Radial Pro D2 boxes, one for the keys, and one for the vox (or can one box be used for both)?

No, the D2 is a two channel box, so it can handle both sources.

2. Clearly I need to engage the "Ground Lift" button(s) if I want to protect against phantom power running from the Soundcraft UI24r back into my Mackie ... right?

No. The outputtransformers in the box prevent phantom from reaching your gear. Usually, you would leave the ground lift deactivated and only isolate the ground if you get hums or buzzes from a ground loop between your gear and foh.

3. Are outputs of the Radial Pro D2 "THRU" and "XLR" still at line levels after the "Ground Lift" button is engaged?

The ground lift switch doesn't affect signal levels. It just isolates the XLR output ground from the TS input/thru grounds to break any ground loop.

The XLR output is nominally mic level (usually a fairly hot mic level) and feeds the FOH.

The Thru output is wired directly in parallel with the input, and would typically be used to feed a backing amp, or tuner pedal etc.

4. Should I use the "THRU" ports or the "XLR" ports to route signals from the Radial Pro D2 to the Soundcraft UI24r? I'm guessing the "XLR" ports, since that's where the "Ground Lift" button is physically located ... ?

Correct.

Your local mixer connects to the TS inputs. You won't need to use the Thru sockets. The XLRs feed the UI24r mic inputs.

5. Do I actually not have to worry about phantom power inadvertently being applied to TRS lines running from my Mackie mixer in to the Soundcraft UI24r ... or is phantom power only able to be applied at XLR inputs on the Soundcraft?

Phantom can only be applied to the SoundcrT's XLRs. So if you use the TRS line inputs on the UI24r there is no problem.... but personally, I like having the comfort of a transformer between my gear and someone else's, and the the D2 DI boxes you also have a very convenient means of isolating grounds if you get groundloop noises — which you couldn't do anything about with direct TRS connections.

6. I think I've read (but can't find that again to confirm, so maybe I just misunderstood) that ground lifting can affect the actual tone of the signal coming out of the Radial Pro D2 - is that a thing, and should I be concerned, or is it only hypothetical?

It's completely nuts! The transformer could potentially affect the tone... but not the grounding switch.

Sorry for so many questions ...

No problem at all. It's what this place is for!

[Aled Hughes]

Phantom is not present on the UI24R’s TRS inputs- all is good!

[alexis]

Such very helpful answers - Thank you, Hugh and Aled!

So many questions answered ... just one or two follow ups if I could please ...

...

3. Are outputs of the Radial Pro D2 "THRU" and "XLR" still at line levels after the "Ground Lift" button is engaged?

The ground lift switch doesn't affect signal levels. It just isolates the XLR output ground from the TS input/thru grounds to break any ground loop.

Ah, I didn't realize these were TS connectors - all the info I saw just said, "1/4". I have colored cables to keep me organized, but they are all TRS - can I use those instead?
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The XLR output is nominally mic level (usually a fairly hot mic level) and feeds the FOH.

To clarify my understanding (or misunderstanding as the case may be): Does this mean that my keys would be coming out of the Radial Pro D2 XLRm at a "fairly hot mic level"? If I had an XLRm-TRS cable and it went into a Soundcraft TRS input - would the signal be too low?
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The Thru output is wired directly in parallel with the input, and would typically be used to feed a backing amp, or tuner pedal etc.

Sorry - does that mean the THRU output is not "transformer protected", and doesn't have a ground lift option?
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5. Do I actually not have to worry about phantom power inadvertently being applied to TRS lines running from my Mackie mixer in to the Soundcraft UI24r ... or is phantom power only able to be applied at XLR inputs on the Soundcraft?

Phantom can only be applied to the SoundcrT's XLRs. So if you use the TRS line inputs on the UI24r there is no problem.... but personally, I like having the comfort of a transformer between my gear and someone else's, and the the D2 DI boxes you also have a very convenient means of isolating grounds if you get groundloop noises — which you couldn't do anything about with direct TRS connections.

What would make you less comfortable not having a transformer between my gear and the UI24r in the situation where the TRS input on the UI24r is used, since phantom power issues are not a consideration? Just the means of eliminating ground loops?
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6. ...The transformer could potentially affect the tone... but not the grounding switch.

Is this just a "listen to see if the tone is affected or not" kind of situation? Or, are there things I can do ahead of time to keep tone changes to a minimum (minimize cable length, e.g.)?
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Sorry for so many questions ...

No problem at all. It's what this place is for!

So grateful - thank you, Hugh!

[Hugh Robjohns]

Ah, I didn't realize these were TS connectors - all the info I saw just said, "1/4". I have colored cables to keep me organized, but they are all TRS - can I use those instead?

Probably... but let me check tomorrow and get back to you (I'm currently lying in a Hotel bed at midnight with a quantity of Bushmills whiskey in me). Most DI boxes have unbalanced inputs, but whether the ring contact is present and/or connected to anything varies with different models. I can check the D2 tomorrow when I get home.

To clarify my understanding (or misunderstanding as the case may be): Does this mean that my keys would be coming out of the Radial Pro D2 XLRm at a "fairly hot mic level"?

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Yes. Instead of nominal instrument level of -10dBu or thereabouts, it will be attenuated through the transformer to -30dBu, or something in that ball park.

And this is perfect because it's feeding a mic preamp designed to accommodate that sort of level.

If I had an XLRm-TRS cable and it went into a Soundcraft TRS input - would the signal be too low?

It would probably be significantly lower than standard line level. Hopefully the line preamp has enough gain available to cope.... but many dedicated line inputson consoles and interfaces don't !

Sorry - does that mean the THRU output is not "transformer protected", and doesn't have a ground lift option?

Correct. The thru socket is wired directly across the input socket.

The idea is that you plug the instrument into the input, and the stage amp into the thru socket, and the result is exactly like plugging the instrument straight into the amp. The DI transformer is effectively taking a 'listen (ie. A split or a 'sniff') of that signal without affecting it in any significant way.

What would make you less comfortable not having a transformer between my gear and the UI24r in the situation where the TRS input on the UI24r is used, since phantom power issues are not a consideration? Just the means of eliminating ground loops?

It's a combination of things. Using a DI box (or a line isolation box) guarantees protection from phantom, and provides easy ground-loop avoidance. Using a DI box also provides a standard mic-level feed on a standard XLR avoiding all possible confusion as to mic or line level, plug format and do on. Just plug straight into a stage box. No worries.

It also provides protection in the event of a major electrical fault in the FOH installation... unlikely, perhaps, but expensively catastrophic if it does occur.

Is this just a "listen to see if the tone is affected or not" kind of situation? Or, are there things I can do ahead of time to keep tone changes to a minimum (minimize cable length, e.g.)?

It is very unlikely you'll hear anything, and your audience will never notice... but there is a reason why Radial offer different passive DI boxes. The ones with Jensen transformers have lower distortion and coloration than those that don't... but they cost significantly more. Input impedance can also make a difference, particularly with high impedance guitar pickups. Not likely to be an issue with low impedance console outputs.

[alexis]

Ah, I didn't realize these were TS connectors - all the info I saw just said, "1/4". I have colored cables to keep me organized, but they are all TRS - can I use those instead?

Probably... but let me check tomorrow and get back to you (I'm currently lying in a Hotel bed at midnight with a quantity of Bushmills whiskey in me). Most DI boxes have unbalanced inputs, but whether the ring contact is present and/or connected to anything varies with different models. I can check the D2 tomorrow when I get home.

...

Two things Hugh -

1. Thank you so much, truly above and beyond!
2. If you like Bushmill's, I will look for it to give it a taste. I've just recently started drinking what we call Scotch here, lucky enough to have some friends with expensive I mean refined tastes who are happy to share! Is that the same as "whiskey" there?
3. I think I may have some info on the above question, here from the Radial FAQ:

https://www.radialeng.com/product/prod2/faq
Q: Can I connect the balanced output from a mixer to the unbalanced input on the ProD2?
A: Yes, but it depends. While the ProD2 is perfectly capable of accepting unbalanced inputs, the use of balanced inputs with the ProD2 can potentially introduce the risk of noise while also causing the output of the balanced signal to be reduced by 6dB when used by the ProD2. Since some mixers have high amounts of output available, you may need to use the Pad switch to compensate in the case of distortion.

So, I guess I need to buy some TS-TS cables to come out of my mixer to feed the Radial Pro D2. I couldn't find any TRS-TS, I guess that wouldn't make any sense anyway ...

Thanks again, Hugh!

[Aled Hughes]

I’m a bit confused now- why don’t you connect directly to the Soundcraft’s TRS inputs? As I said, there is no phantom power on those, so XLR-TRS would be fine.

And Bushmills is Irish whiskey, not Scotch

[Hugh Robjohns]

If you like Bushmill's, I will look for it to give it a taste. I've just recently started drinking what we call Scotch here, lucky enough to have some friends with expensive I mean refined tastes who are happy to share! Is that the same as "whiskey" there?

Bushmills is an Irish whiskey. Whisky made in Scotland doesn't have the 'e'. Irish whiskey has a different — softer — character to Scots whisky, although single malts can vary enormously, of course.

So, I guess I need to buy some TS-TS cables to come out of my mixer to feed the Radial Pro D2. I couldn't find any TRS-TS, I guess that wouldn't make any sense anyway ...

TRS-TS cables can make sense in some situations (such as recording from an insert point)... but it wouldn't help in your situation.

The situation of connecting balanced outputs to unbalanced inputs is always fraught with confusion and complication, basically because different balanced output constructions behave differently when connected to unbalanced inputs — most of it concerning what happens to the cold or ring contact.

If done the wrong way, you could lose 6dB of level in some cases (not all) — but that doesn't usually matter much. More concerning is that you could get some distortion, probably on loud transient peaks. And occasionally, you might even get nothing at all (with floating transformer outputs).

Your mackie probably has impedance-balanced outputs on the aux and group outs, which will work perfectly with an unbalanced connection to the di box.

TS-TS cables are a good idea, though, and as short as practical.

[alexis]

All duly noted, whisky vs whiskey included.

TS-TS cables purchased.

Thank you, Hugh!

[alexis]

Hi Aled -

No direct connection from mic to to Soundcraft because signal is hitting my personal mixer first for IEMs.

Thanks for your help!

[Aled Hughes]

Hi Aled -

No direct connection from mic to to Soundcraft because signal is hitting my personal mixer first for IEMs.

Thanks for your help!

Yes, but can’t you go from your mixer directly to the Soundcraft’s line input?

[alexis]

Hi Aled -

No direct connection from mic to to Soundcraft because signal is hitting my personal mixer first for IEMs.

Thanks for your help!

Yes, but can’t you go from your mixer directly to the Soundcraft’s line input?

I believe absolutely so, I'm using the DI box to ...

...

What would make you less comfortable not having a transformer between my gear and the UI24r in the situation where the TRS input on the UI24r is used, since phantom power issues are not a consideration? Just the means of eliminating ground loops?

It's a combination of things. Using a DI box (or a line isolation box) guarantees protection from phantom, and provides easy ground-loop avoidance. Using a DI box also provides a standard mic-level feed on a standard XLR avoiding all possible confusion as to mic or line level, plug format and do on. Just plug straight into a stage box. No worries.

It also provides protection in the event of a major electrical fault in the FOH installation... unlikely, perhaps, but expensively catastrophic if it does occur ...

In this case Aled since you so kindly checked on your UI24r that it's not possible for phantom power to be applied to TRS inputs, it's the other reasons listed above.

Thank you!

[Aled Hughes]

Hi Aled -

No direct connection from mic to to Soundcraft because signal is hitting my personal mixer first for IEMs.

Thanks for your help!

Yes, but can’t you go from your mixer directly to the Soundcraft’s line input?

I believe absolutely so, I'm using the DI box to ...

...

What would make you less comfortable not having a transformer between my gear and the UI24r in the situation where the TRS input on the UI24r is used, since phantom power issues are not a consideration? Just the means of eliminating ground loops?

It's a combination of things. Using a DI box (or a line isolation box) guarantees protection from phantom, and provides easy ground-loop avoidance. Using a DI box also provides a standard mic-level feed on a standard XLR avoiding all possible confusion as to mic or line level, plug format and do on. Just plug straight into a stage box. No worries.

It also provides protection in the event of a major electrical fault in the FOH installation... unlikely, perhaps, but expensively catastrophic if it does occur ...

In this case Aled since you so kindly checked on your UI24r that it's not possible for phantom power to be applied to TRS inputs, it's the other reasons listed above.

Thank you!

Ah I see. Using TRS-TRS connection from your desk to the UI24R also avoids those issues, with the exception of a "major electrical fault in the FOH installation"... but to be honest you rarely see line levels converted to mic level via DI boxes and then back up to line levels just for this reason. If you're just dealing with line level both ends, be that on XLR or TRS, I'd just go direct from one into the other!

[Hugh Robjohns]

If you're just dealing with line level both ends, be that on XLR or TRS, I'd just go direct from one into the other!

I think it really depends on how much you trust the person controlling the other gear.

In my own studio, and with engineers I trust and know well, I would and do happily run balanced line level directly into the main mixer or interface etc.

With properly engineered balanced gear ground-loops shouldn't be an issue, phantom shouldn't be a risk, duff or dubious gear won't be an issue, so there's no problem... in theory.

But on a stage or in a rehearsal room, with someone else's gear, in the confusion of fast setups in a dark environment, and with people controlling the gear who might not be at the top of their game or might be distracted... personally I wouldn't risk it for the sake of a simple DI box or two at my end.

YMMV

Of course, some people are concerned about the idea of converting line levels to mic level via DI boxes and then amplifying back up to line levels again... thinking noise and distortion will degrade the sound. However, with modern mic preamps and decent DI boxes it's really not the case at a practical level. You could measure a degradation with test gear, but not with your ears on stage, or even in the studio. It's just not an relevant concern any more.

But if it's still a bother, a line isolating transformer box in place of the DI box will confer all the same protective benefits without the level changes.

[Aled Hughes]

If you're just dealing with line level both ends, be that on XLR or TRS, I'd just go direct from one into the other!

I think it really depends on how much you trust the person controlling the other gear.

In my own studio, and with engineers I trust and know well, I would and do happily run balanced line level directly into the main mixer or interface etc.

With properly engineered balanced gear ground-loops shouldn't be an issue, phantom shouldn't be a risk, duff or dubious gear won't be an issue, so there's no problem... in theory.

But on a stage or in a rehearsal room, with someone else's gear, in the confusion of fast setups in a dark environment, and with people controlling the gear who might not be at the top of their game or might be distracted... personally I wouldn't risk it for the sake of a simple DI box or two at my end.

YMMV

Of course, some people are concerned about the idea of converting line levels to mic level via DI boxes and then amplifying back up to line levels again... thinking noise and distortion will degrade the sound. However, with modern mic preamps and decent DI boxes it's really not the case at a practical level. You could measure a degradation with test gear, but not with your ears on stage, or even in the studio. It's just not an relevant concern any more.

But if it's still a bother, a line isolating transformer box in place of the DI box will confer all the same protective benefits without the level changes.

I don't disagree, but in this case it's a matter of handing line outs on TRS jacks to another mixer is a known quantity, and is known to not have phantom power present on the TRS inputs. I know personally I'd take that risk without second thought (as I do when handing out stereo monitor feeds to camera crews etc), but maybe I should be more cautious.

I'm pretty sure Orchid do affordable line isolating transformer boxes in the same housing as their Micro DIs - if Alexis is doing this often maybe a couple of those would be worthwhile (if easily available)

[Hugh Robjohns]

Sure... but he's already got the D2.