DI needed or not - Live Sound

[vgermani]

Hi, I have a live keyboard rig with an off-stage rack that all of my audio goes through. A while back, one of the sound guys recommended this setup. I take the main xlr outs of my X-Air 18 mixer into a balanced stereo compressor (Ashley CLX-52). From there, I would have thought I could take the balanced XLR outs of the compressor directly to FOH. He recommended I go through a DI box before FOH. Not sure if it was for the ground lift or otherwise. I use the Whirlwind Multi-Director DI.

Two questions:
1-Do I really need the DI (and why)
2-If I do, It seems like I would be going from Balanced to Unbalanced, back to Balanced. Is there a better DI solution where I wouldn't need to make so many changes to the system?

Thanks in advance for any help or pointers you may have!

[BertKoor]

Imho for balanced line level signals like you have, a DI is not needed. It adds noise, so skip it.
It were different if you had a unbalanced signal (like the output of the synths themselves) that had to go through the multicable, then a DI is recommended.

To put it into perspective, the main outs of the FOH mixer will also go through a compressor/limiter, then a hundred meters of balanced multicable snake back to stage to feed the PA & monitoring amps. So I fail to see any difference with your setup

[thecontrolcentre]

I would have thought that your mixer outputs will connect to FOH from the PA systems DI box, so you shouldn't need to provide your own DI. That's how its worked at every gig I ever did. Stereo out from my mixer to the venues DI box, then to FOH mixer.

[CrystalWizard]

Yes, they generally provide DI boxes at the venue. They prefer DIs to runinning xlr because DI boxes are electrically isolating (1:1 transformer). That said i have run xlr out of my mixers straight to FOH. I have show up without my mixer for computer only gigs and been told “we don’t have enough direct ins!” I bought a really nice Radial DI box that i now bring along just in case.

[vgermani]

Thanks for the responses. @CrystalWizard, I was starting to wonder if it had to do with transformer isolation. Are there devices that provide transformer isolation without having to change from balanced to unbalanced then back to balanced again (balanced to balanced isolation)?

I have a similar question related to power, since I'm using an isolation transformer for mains power as well, but that's another post

[CrystalWizard]

Yes, there are balanced xlr to xlr

[JCJR]

The di could be desirable for electrical isolation.

OTOH, what do you expect out of the Ashley compressor that you can't get by inserting a built-in compressor instance on the main outs of your digital mixer? Does your sound guy know you already have compressors and eqs and such built-in the digital mixer for free?

I mean, Ashley makes good gear but a bus comp on a live keyboard mixer is not exactly a demanding application and your mixer offers several built in compressors you could try without having to spend more money.

[BertKoor]

Are there devices that provide transformer isolation without having to change from balanced to unbalanced then back to balanced again (balanced to balanced isolation)?

I don't really get what you mean here. Most DI's have balanced inputs & balanced outputs. Transformers are balanced by nature.
At what point in the chain is this "change from balanced to unbalanced" required?

[vgermani]

@BertKoor, I was referencing my current configuration of coming out of the balanced compressor, going into an unbalanced DI input, only to convert it back to balanced. With the above config, I can keep it balanced all the way through. I thought most DIs have unbalanced ins and balanced outs. It seems that there are with some, but the one I'm currently using is all unbalanced in/balanced out.

[vgermani]

oops. ignore

[vgermani]

THANKS! Good point. At the time of this original configuration, I only had a small analog mixer. That's why he suggest the outboard compressor. After doing some reading, I'm guessing adding the DI box between that and FOH would be to isolate the signal. Now that I have the digital mixer, I should be able to eliminate the outboard compressor and DI box. I'm thinking that I will go from the XLR outs of the mixer into a line isolator
Then I won't have to play around with converting balanced to unbalanced signals and back again, I'll have isolation and a ground lift if needed. See any issues with that?

[vgermani]

Looking at the twin-iso from Radial

[JCJR]

Yeah some direct boxes have both balanced and unbalanced inputs. For line-level isolation from your mixer to another mixer, one of the "hum buster" isolation transformer type products would be "about the same thing" as a DI.

For line-level transformer isolation, note that cheap transformers will distort at lower signal levels than better transformers. Such distortion is most audible with low-frequencies and sometimes folks like cheap transformers as an effect because the bass saturation adds harmonics, warms up the lows without much affecting the highs. But IMO its better to find an isolation box that is speced good enough to handle fairly hot line level from your mixer without adding transformer saturation.

I only mention that because some of the cheapest isolation transformers I read about a year or so ago, either did not mention max signal levels or they quoted levels lower than I would personally want in order to assure clean signal. It is hard to "draw the line" because the very best studio-quality low distortion line transformers such as Jensen get real expensive. A DI made mainly for instruments and mics wouldn't need to be built to be low-distortion with hot signal levels.

I suppose most sound guys nowadays take their own electrical distribution systems with them and know how to avoid electrical faults, but you never can tell, and in my opinion better safe than sorry connecting thru hundreds of feet cable. If the AC wiring is incompatible in certain ways between where you are plugged in and where the FOH mixer is plugged in, it could be a bad day involving smoke coming out of your gear. Doesn't happen real frequently but a bummer when it does happen. Could also help with hum somewhat, but for live use I'd mainly be concerned with avoiding frying my gear due to AC wiring faults.

[vgermani]

Thanks again! I really appreciate all of the responses..@JCJR, from what I can tell, the twin iso uses jenson transformers and shouldn't distort under +21db.
http://www.radialeng.com/product/twin-iso
*POWER*, as you mentioned, is another issue. I'm writing another post right now to address that.

Thanks!

[JCJR]

Hi vgermani. That Radial isolation transformer looks like a very good product according to what the web page says!