Soundcraft UI24R - line level into XLR input?

[alexis]

Hi -

I sat in on a session last night with some guys that used the Soundcraft UI24R mixer mentioned in the subject. The session's King of the Soundcraft (guitar player/vocalist who set up the Soundcraft for the 5-6 member band and does remote mixing from his stage position) took a TRS-TRS at line level out from my personal mixer to route my vocals to his Soundcraft, but it seemed like his available TRS inputs were fewer than his XLR inputs and he might have been happier if I'd given him an XLR input instead.

I'll be sitting in again sometime soon, and I thought it'd be nice for him if I used a TRS-Male XLR to run the vocals to his Soundcraft, but then I got to thinking ... are mixers smart enough to know when a signal coming into the XLR is at line level and adjust accordingly?

Thanks for any thoughts!

[adrian_k]

Just looked at the description of this mixer, it has 10 combo inputs (XLR / jack), 10 mic inputs (XLR) and 2 line in (phono).

The combo inputs are happy with TRS, not sure if they are auto switching or switchable mic/line. If auto switching, an XLR to TRS cable would be the worst option as (I think) the mixer would be expecting mic level input on the XLR.

Best to ask the guy what he wants from you?

[Aled Hughes]

As mentioned above, 10 of the Souncraft’s 20 inputs are on combo TRS/XLR.

I’m not sure if the gain ranges for both are different* - I’ll check today if I get a chance.

In any case I’ve happily connected line sources to the XLR inputs (I think the range on them goes down to -6 or -10dB, but yes, best ask them what they’d prefer!

*Out if curiosity, do combo jack/sockets offer separate output wiring for each into different gain stages, or are the jack/XLR connectors simply wired in parallel to the same 3 output connectors?

[James Perrett]

*Out if curiosity, do combo jack/sockets offer separate output wiring for each into different gain stages, or are the jack/XLR connectors simply wired in parallel to the same 3 output connectors?

According to

https://www.neutrik.com/en/product/ncj6fi-h-0

they are completely separate - which ties in with my experience with gear that uses them.

[Kwackman]

I suppose (I've little knowledge in this field) they'd have to be separate, otherwise you'd get phantom power, if switched on, on the TRS jacks?

[Aled Hughes]

I suppose (I've little knowledge in this field) they'd have to be separate, otherwise you'd get phantom power, if switched on, on the TRS jacks?

Ah yes of course, good thinking!

And thanks James for the research I should have done myself

[Hugh Robjohns]

... I thought it'd be nice for him if I used a TRS-Male XLR to run the vocals to his Soundcraft, but then I got to thinking ... are mixers smart enough to know when a signal coming into the XLR is at line level and adjust accordingly?

On the UI24 the top row of inputs are combi XLRs, for line and mic inputs, while the bottom row are just XLR. The line inputs present a 12k Ohm impedance, while most mic inputs are 6k Ohms (1/2 are 4.2k for some reason...).

Most electronic line outputs will be fine feeding 6k...

And to answer someone else's question, the TRS and XLR contacts are normally entirely separate in a combi-XLR, so can feed separate mic and line preamps, or input attenuators, or whatever (and to keep phantom away from the TRS connections).

Usefully, the mic inputs in the UI24R can handle signals up to +19.5dBu, which is a reasonably hot line level, and the gain control can attenuate by 6dB, so it shouldn't have any problem receiving a line signal. There's no automatic mic/line switching, you just set the gain knob appropriately.

So, from a levels standpoint, you could technically use a TRS-XLRm cable to connect your desk line out directly to the UI24 XLR mic input and adjust the mixer input gain accordingly.

But..... XLR inputs can have phantom power on them, and most electronic line outputs aren't very keen to receive phantom power. In some cases it could kill the output stage completely.

As a result, personally, I would never connect a line out directly to the mic input of someone else's gear, ever!

I would trust myself not to accidentally turn phantom power on, but not someone else, especially in the rush and confusion of a rehearsal or live stage situation.

The liklihood of accidentally turning on phantom might be low, but it's not zero, and the outcome could be catastrophic and expensive....

Instead, I would always connect via a DI box or an isolation box — something with a transformer in it to provide galvanic isolation, both to avoid ground loops and to protect against phantom.

[alexis]

... I thought it'd be nice for him if I used a TRS-Male XLR to run the vocals to his Soundcraft, but then I got to thinking ... are mixers smart enough to know when a signal coming into the XLR is at line level and adjust accordingly?

On the UI24 the top row of inputs are combi XLRs, for line and mic inputs, while the bottom row are just XLR. The line inputs present a 12k Ohm impedance, while most mic inputs are 6k Ohms (1/2 are 4.2k for some reason...).

Most electronic line outputs will be fine feeding 6k...

Usefully, the mic inputs in the UI24R can handle signals up to +19.5dBu, which is a reasonably hot line level, and the gain control can attenuate by 6dB, so it shouldn't have any problem receiving a line signal. There's no automatic mic/line switching, you just set the gain knob appropriately.

So, from a levels standpoint, you could technically use a TRS-XLRm cable to connect your desk line out directly to the UI24 XLR mic input and adjust the mixer input gain accordingly.

But..... XLR inputs can have phantom power on them, and most electronic line outputs aren't very keen to receive phantom power. In some cases it could kill the output stage completely.

As a result, personally, I would never connect a line out directly to the mic input of someone else's gear, ever!

I would trust myself not to accidentally turn phantom power on, but not someone else, especially in the rush and confusion of a rehearsal or live stage situation.

The liklihood of accidentally turning on phantom might be low, but it's not zero, and the outcome could be catastrophic and expensive....

Instead, I would always connect via a DI box or an isolation box — something with a transformer in it to provide galvanic isolation, both to avoid ground loops and to protect against phantom.

Thank you, everyone!

My goodness, I had no idea I would have been one button push (phantom power On) on the Soundcraft away from possibly frying my personal mixer, I am so glad I asked - thank you for that warning, Hugh!

...
And to answer someone else's question, the TRS and XLR contacts are normally entirely separate in a combi-XLR, so can feed separate mic and line preamps, or input attenuators, or whatever (and to keep phantom away from the TRS connections).

Just to confirm please: would it be right to say: if I gave him a TRS (line level signal routed from my personal mixer to the Soundcraft) there would be no chance phantom power would hit my personal mixer, even if he plugged it into the Combi-jack, even if I didn't interpose a DI/isolation box ?

Thank you!

[Aled Hughes]

... I thought it'd be nice for him if I used a TRS-Male XLR to run the vocals to his Soundcraft, but then I got to thinking ... are mixers smart enough to know when a signal coming into the XLR is at line level and adjust accordingly?

On the UI24 the top row of inputs are combi XLRs, for line and mic inputs, while the bottom row are just XLR. The line inputs present a 12k Ohm impedance, while most mic inputs are 6k Ohms (1/2 are 4.2k for some reason...).

Most electronic line outputs will be fine feeding 6k...

Usefully, the mic inputs in the UI24R can handle signals up to +19.5dBu, which is a reasonably hot line level, and the gain control can attenuate by 6dB, so it shouldn't have any problem receiving a line signal. There's no automatic mic/line switching, you just set the gain knob appropriately.

So, from a levels standpoint, you could technically use a TRS-XLRm cable to connect your desk line out directly to the UI24 XLR mic input and adjust the mixer input gain accordingly.

But..... XLR inputs can have phantom power on them, and most electronic line outputs aren't very keen to receive phantom power. In some cases it could kill the output stage completely.

As a result, personally, I would never connect a line out directly to the mic input of someone else's gear, ever!

I would trust myself not to accidentally turn phantom power on, but not someone else, especially in the rush and confusion of a rehearsal or live stage situation.

The liklihood of accidentally turning on phantom might be low, but it's not zero, and the outcome could be catastrophic and expensive....

Instead, I would always connect via a DI box or an isolation box — something with a transformer in it to provide galvanic isolation, both to avoid ground loops and to protect against phantom.

Thank you, everyone!

My goodness, I had no idea I would have been one button push (phantom power On) on the Soundcraft away from possibly frying my personal mixer, I am so glad I asked - thank you for that warning, Hugh!

...
And to answer someone else's question, the TRS and XLR contacts are normally entirely separate in a combi-XLR, so can feed separate mic and line preamps, or input attenuators, or whatever (and to keep phantom away from the TRS connections).

Just to confirm please: would it be right to say: if I gave him a TRS (line level signal routed from my personal mixer to the Soundcraft) there would be no chance phantom power would hit my personal mixer, even if he plugged it into the Combi-jack, even if I didn't interpose a DI/isolation box ?

Thank you!

Phantom shouldn’t be present on the jack input… but it sometimes is on some equipment!

Give me 20 minutes and I’ll check if that’s the case on the Soundcraft…

[alexis]

...

Phantom shouldn’t be present on the jack input… but it sometimes is on some equipment!

Give me 20 minutes and I’ll check if that’s the case on the Soundcraft…

Very kind of you, Aled, thank you! I looked at the owners manual .pdf https://www.soundcraft.com/en-US/products/ui24r but didn't recognize where that was addressed.

[Aled Hughes]

...

Phantom shouldn’t be present on the jack input… but it sometimes is on some equipment!

Give me 20 minutes and I’ll check if that’s the case on the Soundcraft…

Very kind of you, Aled, thank you! I looked at the owners manual .pdf https://www.soundcraft.com/en-US/products/ui24r but didn't recognize where that was addressed.

All good, phantom power is not present on the TRS jack inputs.

[Hugh Robjohns]

The convention is that phantom should only ever be present on XLRs capable of working with mic level signals, and never on TRS sockets or the jack centre of a combi-XLR....

The majority of manufacturers —:especially all the big names — uphold that convention... but I have come across some products where phantom does appear on TRS sockets and combis... smaller and niche manufacturers are the most likely culprits.

So, never assume and if it matters, check or protect!

[shufflebeat]

I would trust myself not to accidentally turn phantom power on…

Me too, unfortunately it turns out my trust was misplaced.

I managed to avoid completely frying… an item, but not sure how, just lucky this time.

Lesson learned? Dr H’s DI box/osolator suggestion - every time.

[alexis]

...
All good, phantom power is not present on the TRS jack inputs.

Thank you, Aled! I was wondering ... is that something you inferred from the manual, or did I just plain miss it when I went through it?

Much appreciated!

[Aled Hughes]

...
All good, phantom power is not present on the TRS jack inputs.

Thank you, Aled! I was wondering ... is that something you inferred from the manual, or did I just plain miss it when I went through it?

Much appreciated!

No, I checked on my unit. All seems well, unless the XLR-TRS cable I used was somehow blocking phantom power.

[alexis]

...
All good, phantom power is not present on the TRS jack inputs.

Thank you, Aled! I was wondering ... is that something you inferred from the manual, or did I just plain miss it when I went through it?

Much appreciated!

No, I checked on my unit. All seems well, unless the XLR-TRS cable I used was somehow blocking phantom power.

Thanks again, Aled!