Do I need two DI boxes?

[alexis]

Hello,

I have one vocal signal and two keyboard outputs (L/R) coming out of my personal Mackie mixer (ProFXV3+), routed to a Soundcraft ui24r.

After leaving the mixer, the vocal signal is routed through a Radial ProD2 stereo passive DI on the way to the ui24r (leaving one Radial channel unused). I'm doing this to protect against power surges that might come from the ui24r and damage the Mackie, with the "GROUND Push to lift" button pushed in (is that the part of the DI box that gives protection, or is that button just to prevent hum from feedback loops?).

My keyboard outputs go directly from the Mackie to the ui24r, without protection against power surges.

I'm wondering: do I need to buy another DI to accommodate my keyboards outputs for protection of the Mackie against power surges?


Or is it unnecessary to send my vocal signal through a DI box (after it leaves the Mackie), freeing up both Radial DI connections to be used for my two keyboard outputs?

Thank you!

PS: I use a condenser mic, Earthworks SR117, with phantom power on at my mixer. It's there any risk of damage if the ui24r is inadvertently programmed to also deliver phantom power?

[Tomás Mulcahy]

Yes the DI box for the vocal signal is not necessary. Ground lift is only to get rid of the annoying buzz caused by a ground loop. It is not a safety feature for power surges nor is it to prevent feedback.

Power surges are rare but if you really need protection, a good UPS will do it. But I personally would not bother.

Use a TS or TRS cable to feed the audio interface. There is no phantom power on a Jack cable.

[Hugh Robjohns]

After leaving the mixer, the vocal signal is routed through a Radial ProD2 stereo passive DI on the way to the ui24r (leaving one Radial channel unused). I'm doing this to protect against power surges that might come from the ui24r and damage the Mackie

This is a sensible precaution in a live sound situation... but completely pointless if you have other direct connections between your mackie and the house soundcraft!

... with the "GROUND Push to lift" button pushed in (is that the part of the DI box that gives protection, or is that button just to prevent hum from feedback loops?).

It's the transformer in the DI box that provides 'protection'.

The ground-lift button helps to prevent noise from ground currents caused by a ground-loop.

A feedback loop is a very different thing...

My keyboard outputs go directly from the Mackie to the ui24r, without protection against power surges.

I'm wondering: do I need to buy another DI to accommodate my keyboards outputs for protection of the Mackie against power surges?

If you want 'protection' from electrical risks then yes, something with transformers would be good. A DI box would provide mic-level outputs, or a line-isolation box would maintain line-level connections.

Or is it unnecessary to send my vocal signal through a DI box (after it leaves the Mackie), freeing up both Radial DI connections to be used for my two keyboard outputs?

I thought we'd been through all the reasons and options for DI boxes and line isolators.

The transformers provide protection against electrical malfunctions at the destination and prevent phantom power from the destination reaching the source.

They also provide the option to separate source and destination grounds to reduce the risk of ground-loop noise.

A DI box takes an unbalanced instrument or line-level source and converts it to a balanced mic-level signal.

A line-isolation box takes a balanced or unbalanced line-level input and converts it to a balanced or unbalanced line-level output.

I think we've discussed the pros and cons of direct connections before... but my personal view when working in any and all live-sound situations (as opposed to the more controlled and reliable studio) is to always connect via some sort of transformer isolation.

And, to keep things simple and familiar, I prefer to always provide balanced mic-level signals to FOH... which means DI boxes for every connection.

So, in your case, I would therefore use the D2 for the stereo keyboard feed, and acquire a D1 (or similar) for the mono vocal feed.

I use a condenser mic, Earthworks SR117, with phantom power on at my mixer. Is there any risk of damage if the ui24r is inadvertently programmed to also deliver phantom power?

I think you're connecting a line output from your mackie mixer to pass the vocal signal to the house soundcraft. So there's no chance the house phantom will ever reach the mic — there's masses of electronics in the way.

However, there is a risk of phantom damaging the mackie's line outputs... which is why you connect via a DI box.

[ef37a]

"However, there is a risk of phantom damaging the mackie's line outputs... which is why you connect via a DI box."

You have just given me pause Hugh! My son's A&H ZED10 uses male XLRs for its Main Mix outputs it therefore occurs that it would be very easy for them to be connected by some dimwitted ASM to a mic input with a standard mic cable!
It is more usual these days I think to only use XLRs for mic inputs at least on "prosumer gear"? Being an A&H mixer they are perhaps "a cut above" and so include some protection?

He has only gigged the mixer once and does not want to do so again as it is sort of integrated into his home recording setup.

Dave.

[Tomás Mulcahy]

Oh it's a Soundcraft mixer. Somehow I overlooked that and thought it was a Behringer UMC series interface you were mentioning. Can mods please delete my post it is confused

[tacitus]

And, to keep things simple and familiar, I prefer to always provide balanced mic-level signals to FOH... which means DI boxes for every connection.

This. I find it horribly easy to forget what’s at line level, with potential loud consequences, so having everything at the same mike level is a boon, especially if circumstances force a last-minute change of channels …

So yes, two DI’s (and more) is a good plan. Better to have one left over than be one short.

[alexis]

Thank you Hugh, tacitus, Tomas, and Dave!
.

...

It's the transformer in the DI box that provides 'protection'.

The ground-lift button helps to prevent noise from ground currents caused by a ground-loop.

A feedback loop is a very different thing...

I've wondered ... isn't lifting the ground dangerous?

(Right, thanks, I don't know why I wrote "feedback").

...
If you want 'protection' from electrical risks then yes, something with transformers would be good. A DI box would provide mic-level outputs, or a line-isolation box would maintain line-level connections.

Or is it unnecessary to send my vocal signal through a DI box (after it leaves the Mackie), freeing up both Radial DI connections to be used for my two keyboard outputs?

...

The transformers provide protection against electrical malfunctions at the destination and prevent phantom power from the destination reaching the source.

They also provide the option to separate source and destination grounds to reduce the risk of ground-loop noise.

A DI box takes an unbalanced instrument or line-level source and converts it to a balanced mic-level signal.

A line-isolation box takes a balanced or unbalanced line-level input and converts it to a balanced or unbalanced line-level output.

And, to keep things simple and familiar, I prefer to always provide balanced mic-level signals to FOH... which means DI boxes for every connection.

So, in your case, I would therefore use the D2 for the stereo keyboard feed, and acquire a D1 (or similar) for the mono vocal feed.

.
We're out of mic inputs on the Soundcraft ui24r ... so would using a line isolation box (instead of a DI box) to avoid mic level signals going into a 1/4" port expecting a line level signal be the right thing to do?

Thank you again!

[ef37a]

Alexis, you can get XLR mic to near line level transformers quite cheaply.
These give about an 18dB boost but that varies with brand. They are sold as "low to high impedance matching transformers. 600Ohms to 50k"

Not the highest fidelity of devices but they can get you out of a hole if you run out of mic inputs. You need to put fairly hot signals down them as line input don't usually have a lot of gain. Should work ok though with a kick or mic on an amp.

https://www.amazon.co.uk/Soundlab-G132C ... d_source=1

Dave.

[Hugh Robjohns]

I've wondered ... isn't lifting the ground dangerous?

Cutting or isolating a mains safety ground is extremely dangerous... but that's not what a ground-lift switch does. It only affects the audio reference ground, either separating it from a mains safety ground, or (less often) separating one audio reference ground from another.

We're out of mic inputs on the Soundcraft ui24r ... so would using a line isolation box (instead of a DI box) to avoid mic level signals going into a 1/4" port expecting a line level signal be the right thing to do?

Yes. I'd use something like an ART DTI box.

Short unbalanced TS-TS cables from keyboard to box inputs. Then XLRf-TRS from box outpurs to console TRS line inputs.

[Sam Spoons]

I've wondered ... isn't lifting the ground dangerous?

(Right, thanks, I don't know why I wrote "feedback").

Lifting/removing a safety earth, i.e. the one in the mains cables, is dangerous and something that should never be done, lifting an audio earth in a balanced cable is fine.

.
We're out of mic inputs on the Soundcraft ui24r ... so would using a line isolation box (instead of a DI box) to avoid mic level signals going into a 1/4" port expecting a line level signal be the right thing to do?

Thank you again!

Yes, a line isolator would be the right bit of kit to use.

[alexis]

Thank you, Hugh and Sam!
.

I've wondered ... isn't lifting the ground dangerous?

Cutting or isolating a mains safety ground is extremely dangerous... but that's not what a ground-lift switch does. It only affects the audio reference ground, either separating it from a mains safety ground, or (less often) separating one audio reference ground from another.

We're out of mic inputs on the Soundcraft ui24r ... so would using a line isolation box (instead of a DI box) to avoid mic level signals going into a 1/4" port expecting a line level signal be the right thing to do?

Yes. I'd use something like an ART DTI box.

Short unbalanced TS-TS cables from keyboard to box inputs. Then XLRf-TRS from box outpurs to console TRS line inputs.

.
If I may please, three follow up questions:

1) Is the XLR output from the ART DTI, and the Radial Pro DT2, at mic level? If so, I'm trying to understand why plugging it into the 1/4" input on the ui24r wouldn't be a problem, since it's (presumably?) expecting line level?

2) I was wondering if one of these DI boxes (below, maybe the Radial Stagebug-sb6 for its increased connection flexibility over the sb2?) would be just as good as the ART DTI? The only reason I'd be interested in them is that my vocal DI box is a Radial D1 (ordered this weekend), and my mic splitter is an ART. So it might make set up just a tiny bit more immune to "Oops!" if I had all my DI functionality be one brand (Radial), and the mic splitter be a different brand (ART).

Weak reason, I know, but if there's a way to simplify things I'd tend to be all for it! #eyeroll

https://www.radialeng.com/product/stagebug-sb2

https://www.radialeng.com/product/stagebug-sb6

3) If it somehow is better for me to use the ART DTI than the Radial Stagebug DI box: the ART DTI seems to also have 1/4 outputs in addition to XLRs, so could I run my keyboard signals through the DTI to the ui24r via two TRS cables?

Thank you again!

PS: Thank you for explaining that the audio ground is different than the voltage ground, and so the former is safe to lift!

[Hugh Robjohns]

1) I was wondering if one of these DI boxes (below, maybe the Radial Stagebug-sb6 for its increased connection flexibility over the sb2?) would be just as good as the ART DTI?

The Radial SB6 would be a suitable alternative.

2) If it somehow is better for me to use the ART DTI than the Radial Stagebug DI box: the ART DTI seems to also have 1/4 outputs in addition to XLRs, so could I run my keyboard signals through the DTI to the ui24r via two TRS cables?

I've not compared prices, but I imagine the Radial is more expensive than the ART, but its also probably of a higher quality and has some useful additional features.

The nice thing about the DTI is its plethora of connectors which makes it very versatile in terms of how it can be connected, and flexible in allowing signal duplication and splitting as well.

And yes, you could use the balanced TRS outputs from the DTI rather than the XLRs. The Radial RB6 uses TRS outputs too, or course, as does ART'S CleanBox2.

[alexis]

1) I was wondering if one of these DI boxes (below, maybe the Radial Stagebug-sb6 for its increased connection flexibility over the sb2?) would be just as good as the ART DTI?

The Radial SB6 would be a suitable alternative.

2) If it somehow is better for me to use the ART DTI than the Radial Stagebug DI box: the ART DTI seems to also have 1/4 outputs in addition to XLRs, so could I run my keyboard signals through the DTI to the ui24r via two TRS cables?

I've not compared prices, but I imagine the Radial is more expensive than the ART, but its also probably of a higher quality and has some useful additional features.

The nice thing about the DTI is its plethora of connectors which makes it very versatile in terms of how it can be connected, and flexible in allowing signal duplication and splitting as well.

And yes, you could use the balanced TRS outputs from the DTI rather than the XLRs. The Radial RB6 uses TRS outputs too, or course, as does ART'S CleanBox2.

Thanks, Hugh!

Radial SB6: $150US
ART DTI: $80US

Dang! The ART has all those extra connector options (XLR, TRS, RCA; vs TRS only on the Radial). The quality of the Radial sound (= transformer quality?) must be light years better (...?)

Since I'm fussing all about the piano sound quality I'm thinking I may as well spend the extra $ on the Radial (lifetime investment, the difference in price after all being half the cost of a dinner out for two) ...

One last question please, from earlier: Does the output voltage of the ART DTI depend on which connector is accessed - i.e., is mic voltage output if the XLR outs are used, line voltage output if the 1/4" output is used, etc.?

Thank you again!

[Hugh Robjohns]

Radial SB6: $150US
ART DTI: $80US

Yeah, that figures!

The quality of the Radial sound (= transformer quality?) must be light years better (...?)

Sadly, it's a case of diminishing returns. To get a little better performance costs a lot more. We're talking lower distortion (especially at low frequencies) and more headroom.

Since I'm fussing all about the piano sound quality I'm thinking I may as well spend the extra $ on the Radial (lifetime investment...

...and it fits with your Radial DI simplicity policy!

I've always found Radial gear to be well-engineered and rugged (although for full transparency I know not everyone here has enjoyed the same experience), so the investment should serve a lifetime.

Does the output voltage of the ART DTI depend on which connector is accessed - i.e., is mic voltage output if the XLR outs are used, line voltage output if the 1/4" output is used, etc.?

Nope. All the input connectors are wired together, and to the primary or a 1:1 ratio transformer. Similarly, the secondary of the transformer is wired to all the output connectors.
So they all carry the same, identical signal level.

[alexis]

...

Does the output voltage of the ART DTI depend on which connector is accessed - i.e., is mic voltage output if the XLR outs are used, line voltage output if the 1/4" output is used, etc.?

Nope. All the input connectors are wired together, and to the primary or a 1:1 ratio transformer. Similarly, the secondary of the transformer is wired to all the output connectors.
So they all carry the same, identical signal level.

Super, thank you, Hugh!

(Oh ... sorry, how would I know if the ART DTI outputs are all at line, vs. mic, level? I'm assuming line, since iirc an XLRf to TRSm cable was discussed as a potential connection from the ART DTI to the 1/4" input on the ui24r ... but of course I'm not sure!)

[Hugh Robjohns]

It's a 1:1 ratio transformer, meaning the output is the same level as the input.

It's optimised for line level, but if you put mic level in you'll get mic level out.

[alexis]

It's a 1:1 ratio transformer, meaning the output is the same level as the input.

It's optimised for line level, but if you put mic level in you'll get mic level out.

I'm so happy to know all this - thank you, Hugh!

Armed with your lesson material I'm going to look for "schematics" of the box to reverse engineer my understanding of how to read those things )

[Hugh Robjohns]

Armed with your lesson material I'm going to look for "schematics" of the box to reverse engineer my understanding of how to read those things )

Here it is...

The transformer in the middle is shown with primary (input) and secondary (output) windings of equal length, indicating a 1:1 ratio. The black dots show the 'in-phase' end of each winding

(A step-down transformer, such as used in a DI box, would have a smaller secondary winding. The ratio might be 4:1, for example. A step-up transformer, such as on the input to a mic preamp, would have a smaller primary winding and a ratio of 1:6, perhaps.)

For the input side the 'hot' terminals (TRS tip, XLR pin-2 and centre of the RCA-phono socket) all connect to the in-phase end of the primary winding. The cold terminals (TRS ring, XLR pin-3, and RCA-phono sleeve) all join to the opposite end of the primary.

The input ground connections (TRS sleeve and XLR pin1) join together and to a case ground stud, but go nowhere else.

The output side connectors are wired in exactly the same way to the secondary winding. The TRS and XLR grounds are joined together, but isolated from both the case and the input ground — effecting a permanent ground-lift.

The resistor and capacitor shown wired in series across the secondary winding is called a Zobel Network, and it's there to ensure a flat frequency response by damping the inherent high frequency resonance of the transformer.