DI box for gig - Is this the right setup?


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Hi there - I'm new to this forum, so hello all!

My band is playing a gig this weekend with a slightly new setup involving a DI box, and I'm just looking for some expertise...

I currently play a Roland RD-800, which has 2x 1/4" jack outputs (L/MONO, R) and 2x XLR outputs (L, R). I usually go straight into the PA via our powered mixer (Behringer Europower PMP580S) with a 1/4" jack lead into the line-in input. We have previously had the mixer up on stage with us, or close-by.

However, at our upcoming gig the mixer will positioned further away (approx 10m back from the stage) with someone adjusting our levels live. I've been concerned that this is too far away to reliably run a jack lead (most people say this will result in too much noise) and therefore I've recently ordered a passive DI box (Behringer DI400P) and a 10m XLR lead, hoping that this is a more appropriate setup, with the idea being that I will run a 1/4" mono jack into the DI box

I'm a complete novice when it comes to DI boxes, so please bear with me! My questions are:

  • General setup: Is this the best connection setup for my needs? Have I bought the right kit to reliably/safely run a longer distance cable to our PA? Does it matter whether I run a TS or TRS cable into the DI box?

  • Phantom power: In an ideal world, I could presumably run a direct XLR-XLR from my Roland into the mixer, but we use a phantom power setting for some our microphones, which I understand is a risk to keyboards. Will this DI setup therefore protect me from the phantom power? Are there any factors such as cable types (or the ground/lift switch) which I need to be aware of?

  • Which input? Our mixer has several mono channels (1-6) with XLR inputs marked 'Low-Z', and channels 7/8 & 9/10 that have XLR inputs marked 'Mic' alongside 'L/R' 1/4" line-in inputs. Would it be better to go from the DI box into the 'Low-Z' or 'Mic' XLR inputs?
Many thanks in advance! :)
 
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It's probably a good idea to understand exactly what a DI box does, the two different kinds, and which/when to use them.

DI boxes essentially do two things:
A) The most obvious (but surprisingly the less important) is that they convert 1/4" plugs to XLR. Obviously this is necessary, but technically, the type of plug isn't really all that important. XLRs are more durable, resistant to wear and tear, and more commonly used, but theoretically a 1/4" TRS (3-pole) cable can deliver exactly the same signal under the right conditions. But this isn't particularly important to dwell on, XLR is going to be your best bet.

B) The most important thing is that DIs translate what's called an "unbalanced" signal to a "balanced" signal. The concept is a bit confusing at first, and usually takes people a little bit to get their head around, read up on how it works if you wish (when it finally clicked for me, I realized it was really ingenious and cool). But the short of it is that by splitting the signal into two copies and inverting their waveform polarity, you can GREATLY reduce the amount of noise incurred by long cable runs. All cables act as radio receivers, taking in radio, TV, and even cosmic background radiation. The longer the cable, the more surface area to pick up noise. So unbalanced runs should be kept to a minimum length.

C*) This is less talked about, but DIs also serve for impedance matching and gain boosting, but this isn't as much of an issue for active units like keyboard and computer outputs, which are actually even above line level.

Now, there are essentially two types of DIs: Passive and Active. Passive make up a good 75% of all the DIs you'll find out there, particularly house equipment. They require no power of their own (phantom or battery), they are a simple magnetic coil transformer. They're far cheaper to make (about half to 2/3 the price of an active), and will usually sufficed for most applications at least fairly well. Active DIs are powered by an internal battery or by Phantom power from the board to do their transforming. They are probably the better option for low-signal level sources like a bass guitar with passive pickups, because they can also impedance match and boost the gain on the low-output source.

A good rule of thumb is: Active source -> Passive DI (or either, really). Passive Source -> Active DI. But either will work. The majority of bass guitars have passive pickups, and the majority of DIs they often will plug into (if they're not going through their amp first) are passive, but they could probably sound a little better with an active. Keyboards, computers, and other electronic devices all have high-output circuitry (usually high enough for driving tiny speakers like headphones), and will be absolutely perfect for passive DIs.

Do you NEED to run a DI if you're 1/4" cable is long enough to reach the amp?
I'm actually gonna disagree with "Cowboy" and say, "No... maybe". From an audio quality and electronics standpoint, if you can run a 10ft 1/4" cable to an amp, or run the same cable to a DI, the signal-to-noise ratios will be identical. As long as you keep your output level on your device no more than 2/3rds full volume, you should also be delivering them a signal that won't overdrive the board, and the impedance should be well within respectable ranges. HOWEVER, from a SAFETY standpoint at a gig, unless you're literally right next to the board, it can be worrisome, as it would be much easier to trip over them and damage your jack. In low-key rehearsals, I often just run 1/4" right by the board, but I wouldn't recommend it for gigs if you have the option not to.

Fear of the Phantom:
For the cases we're talking about, there is absolutely NO concern of hurting your device with fantom power. Fantom Power will end at a DI. It will power an active DI, and be completely unused on a passive DI. Furthermore, 1/4" inputs on boards are almost always unbalanced 2-pole inputs, incapable of phantom. And the few stereo jacks are specifically for receiving from stereo jacks... once again, unbalanced where phantom power isn't a thing. The ONLY time you could ever receive phantom power into your device is if you do something really strange (i.e.: stupid), and run an XLR cable from the board directly into a simple 1/4" converter (not a DI, just a little plug thing) into your board. THEN you're running directly from the phantom-capable XLR output from the board directly into your device. NEVER DO THAT. And it would be stupid anyway. If you want to plug directly into the board, always use 1/4" jacks if available (some boards, especially higher end ones, don't even have them), otherwise use a DI.

In short... get a DI, a simple passive will run you $30 for a decent one, and they're incredibly useful, and cut down headache. Best of all, you can rest easy you will never have to setup close enough to the board for your 10ft cable to reach.

So when does balance REALLY matter? The lower the signal, the more noise can get through. Microphones are INCREDIBLY low signal output, having a tiny magnet and tiny membrane. They go to balanced IMMEDIATELY and have to stay that way until the board. In fact, unproperly shielded plugs and jacks are enough to bring in audible noise, it's that critical. Instrument-level instruments can run a bit further, 10ft is pretty common, after that, it's better to go balanced. Active-circuitry can go even a bit further. Line-level can go even a bit further, headphone-level (which is most keyboards) can even go a bit further. Lastly, speaker cable (which we're talking about 10-100s of Watts) can literally go FOREVER, there is no reason to balance speaker cable, they're a few million times power powerful than a microphone level, and the noise they will receive will be a tiny blip.
 
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Do you NEED to run a DI if you're 1/4" cable is long enough to reach the amp?
I'm actually gonna disagree with "Cowboy" and say, "No... maybe".
No I agree with you, Eric. But remember, sound quality is not the only benefit a DI box brings.

You also don't "need" to lock your car when you're loading in/out at your gig. But I still recommend you ALWAYS do it.

I will not/do not gig without a DI.
 
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Thank you very much for the really useful responses, hugely appreciated! This has added clarity to the research I'd already done and makes me more confident it's the right setup to go for!

Regarding the correct XLR input on the PA, would you suggest putting the DI box into the XLRs marked 'Low-Z' (1-6) or one marked 'Mic' (7/8, 9/10)? (See attached image of PA inputs). Not sure if it matters too much, and now that I know this setup is 'safe' I guess I can just trial-and-error...

Thanks again - Gig is tonight! :)
 

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I can't see the pic on my phone but had a quick look on line at your manual. They're all standard XLR inputs and will work fine.
 
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Well, the gig was last night and the DI box worked a treat - Did exactly what I needed with a fairly long cable run to the mixer (and importantly, no phantom power disasters..!). What's more, the 'thru' jack output on the DI400p was also a lifesaver as it enabled me to hook up an extra keyboard monitor last-minute due to a less-than-ideal stage setup! I'll definitely be taking the DI with me to all future gigs... (Though would agree with Eric that a short 1/4" jack for rehearsal is fine, given that the signal-to-noise would be identical).

Incidentally I went into the channel 7/8 'Mic' input. I'm somewhat confused as to why an XLR input is on a stereo channel, as I understand that 3-pin XLRs are virtually always designed for balanced mono signals. Perhaps the channel is only 'stereo' when using the L/R 1/4" line inputs...

Anyway, worked well! Many thanks again for the tech help!
 
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No I agree with you, Eric. But remember, sound quality is not the only benefit a DI box brings.

You also don't "need" to lock your car when you're loading in/out at your gig. But I still recommend you ALWAYS do it.

I will not/do not gig without a DI.
Definitely not wrong here. My thoughts is it's fine for rehearsals and practices, but
 
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Suspect you’re intuitions at correct. They just slapped an XLR jack to inout 7, even though it was controlled through a stereo channel stripped
 

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