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Live looping rig - balanced v unbalanced

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Live looping rig - balanced v unbalanced

Postby millipz » Tue Jul 21, 2020 9:01 pm

Hi! Newcomer here. I had a quick look at the rules and I think it's okay to just post a new topic for help, but if not, let me know where it should go!

I'm putting together a rig for live looping, involving guitar, vocal mic, an OP-Z synth and some effects. This is a side project, and I would be doing all the vocals and instruments myself. Loading up pre-prepared beats and jamming on the OP-Z while layering vocals and guitar.

Here is the rig:

Image

My plan is to have a 3m snake between the pedalboard/gear and the mixer (Behringer X18), allowing for flexible placement.

I want to place the looper on a send-return to keep things flexible.

My looper is Ditto X4, which has stereo unbalanced TS in and out. My questions are:

1. Do I need DI boxes or reamping boxes anywhere? I'd like to avoid reamping boxes if I can as they seem to be quite costly

2. Will my unbalanced signal to and from the X4 suffer in the 3m to and from the mixer?

3. Any other comments on the setup?

Thanks!
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Re: Live looping rig - balanced v unbalanced

Postby resistorman » Wed Jul 22, 2020 3:57 am

Welcome, and thanks for the diagram! The answer to all 3 questions from me is no.
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Re: Live looping rig - balanced v unbalanced

Postby millipz » Wed Jul 22, 2020 7:16 am

No problem, I’m visual thinker. Thanks for taking the time to respond! :thumbup:

That’s a pleasingly succinct first reply! Sounds like I can order my cables then and see how it goes. I’ve already tried looping the OP-Z with midi sync and it works tolerably well. Hopefully I can mix in and out of different grooves using the looper. Such fun!
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Re: Live looping rig - balanced v unbalanced

Postby Hugh Robjohns » Wed Jul 22, 2020 9:58 am

millipz wrote:My questions are:

1. Do I need DI boxes or reamping boxes anywhere? I'd like to avoid reamping boxes if I can as they seem to be quite costly

2. Will my unbalanced signal to and from the X4 suffer in the 3m to and from the mixer?

3. Any other comments on the setup?

I largely agree with Resistorman; my answers would be No, No, and Yes!

No, you don't need DI or Reamping boxes to connect your looper and synth to the mixer. Those devices produce (more or less) line level signals which are not troubled by input impedances, and the mixer can cope with unbvalanced sources and destinations perfectly well.

No, you are very unlikely to suffer from external interference breaking into your line level unbalanced signals over a 3m snake... but do try and keep it away from potentially nasty interference sources like lighting cables...

Yes, I do have another comment on the setup.

When connecting unbalanced devices there is always a possibility of creating ground-loops if two or more of those devices are 'class-1' -- meaning devices with a mains safety ground connection. The XR-18 mixer is definitely a class-1 device.

The Looper and GTX appear to run off wall-warts and are probably class-2 devices, which means they don't have a mains safety ground connection. That's a good thing in your situation as it means they cannot create ground-loop problems!

To check for sure, their power supplies should have the 'double-insulated' 'box-within-a-box' graphic symbol.

Here are the standard symbols for class-1 and class-2 devices:
Image

If you're running the Op-Z on batteries, there's obviously no mains earth connection there either, and so no possibility of any ground-loops via the source equipment. However, if you run it via USN from a laptop or external supply, you'll need to be careful about a possible mains ground connection via that path.

The only other (very small) potential for a ground-loop problem is via the mixer's output to whatever it's feeding... but if you use balanced XLR cables and feed balanced inputs you shouldn't have a problem there either.

And finally, drawing a connection diagram like yours is always a good idea when it comes to planning out connections, noting the cable types required, and spotting potential problems... but it's very helpful to include the powering arrangements too, noting which devices are class-1, which are class-2, and which are powered via a battery or USB etc. This helps to keep an eye on potential ground loop issues, as well as making sure you have the right power supplies, mains cables, and sufficient sockets on the plugboard!
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Re: Live looping rig - balanced v unbalanced

Postby millipz » Wed Jul 22, 2020 10:36 am

Hugh Robjohns wrote:And finally, drawing a connection diagram like yours is always a good idea when it comes to planning out connections, noting the cable types required, and spotting potential problems... but it's very helpful to include the powering arrangements too, noting which devices are class-1, which are class-2, and which are powered via a battery or USB etc. This helps to keep an eye on potential ground loop issues, as well as making sure you have the right power supplies, mains cables, and sufficient sockets on the plugboard!

Hi Hugh, thanks so much for taking the time to read and write such a detailed response! It seems to be a lively and helpful community you have here, really appreciate it.

I will definitely read up on ground loops, and your summary is super helpful. I'm a nerd in many other areas but my electronics knowledge is very patchy. I will also add the power arrangement to my sketch. A couple of followups if I may, as you've been so helpful!

1. At what distance would the unbalanced connection begin to be an issue? This may be somewhat subjective and need testing. Is it a case of external interference or will the cables in the snake start to affect each other?

2. Linked to the above, I am considering plugging the "wall warts" as you colourfully call them into a PDU, rack mounted with the XR18, and running power (barrel plug extensions) through the snake to the pedals. Maybe also a USB A extension cable for power to the OP-Z. might these power runs cause interference?

Thanks again!

Miles
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Re: Live looping rig - balanced v unbalanced

Postby millipz » Wed Jul 22, 2020 10:49 am

Forgot to mention, as an upgrade I am also considering running a MIDI cable through the snake to control the XR18 with a MIDI pedal. I presume MIDI cables are not too bad for interference? Thanks, M
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Re: Live looping rig - balanced v unbalanced

Postby Hugh Robjohns » Wed Jul 22, 2020 11:26 am

millipz wrote:It seems to be a lively and helpful community you have here...

It is -- there are a lot of very knowledgeable and talented people here who enjoy helping others in a kind and supportive way. It makes this a very different and special forum from most of the others out there!

I will definitely read up on ground loops...

A 'ground-loop' is formed when two class-1 mains-powered devices are connected together via audio cables. What happens is that there is always some AC current flowing in the earth wires of the building's mains wiring. Any length of cable has some inherent resistance, and current flowing through a resistance creates a voltage difference across it. So when you plug one device into one mains socket, and another device into a different one, their mains safety earth connections are at slightly different voltages. If you then join those two devices with an audio cable, the shield of the cable effectively links their earths together and, as they are at different voltages an AC current flows in the audio cable's shield.

The ground-loop current flows from the building wiring, into one device via its mains cable, through the audio cable to the other device, and through that device's mains cable back into the building's wiring. hence the 'loop'.

Now, if the audio cable is a balanced one, the wanted audio signal is kept entirely separate from the cable ground -- it flows back and forth only over the hot and cold signal wires -- and there's no problem. (Well, actually there can be sometimes, but only if the equipment isn't designed and built properly!).

However, an unbalanced signal flows back and forth over the signal wire and the cable shield... but if there is a ground-loop current already flowing in the shield as well that inherently gets added to the wanted audio signal -- and that's when you hear those nasty hums and buzzes. And it doesn't take much ground loop current to make a nasty noise on an audio signal!

1. At what distance would the unbalanced connection begin to be an issue? This may be somewhat subjective and need testing. Is it a case of external interference or will the cables in the snake start to affect each other?

Crosstalk between cables isn't likely to be a problem even with 10 or 20 metres. What makes the difference is the destination (and source) impedance, the signal level, and the environment. The greatest risk is from external RF interference, so the nastier the environment, the higher the impedances involved, the lower signal levels, and the longer the cable all increase the risk of problems.

But if you keep the cables away from anything radiating nasties, work with normal line level signals and standard line interface impedances, you should be able to run out to 30 feet or more without problems. Shorter is always better, though!

2. Linked to the above, I am considering plugging the "wall warts" as you colourfully call them into a PDU, rack mounted with the XR18, and running power (barrel plug extensions) through the snake to the pedals. Maybe also a USB A extension cable for power to the OP-Z. might these power runs cause interference?

I'd hope not, but it depends on the quality of the power supplies! bear in mind that you may end up losing power voltage if you extend the supplies over long cables, potentially resulting in reduced headroom, lower output levels, and less reliability... So test carefully before committing!
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Re: Live looping rig - balanced v unbalanced

Postby millipz » Wed Jul 22, 2020 4:25 pm

Fantastic! Thanks so much. I’m going to order what I need for a 3M snake, set up and get testing. Will report back. M
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Re: Live looping rig - balanced v unbalanced

Postby resistorman » Wed Jul 22, 2020 7:23 pm

Keep in mind that wall warts and line lumps will likely cause noise if you run unbalanced audio near them.
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Re: Live looping rig - balanced v unbalanced

Postby AlecSp » Thu Jul 23, 2020 11:41 am

Hugh Robjohns wrote:I'd hope not, but it depends on the quality of the power supplies! bear in mind that you may end up losing power voltage if you extend the supplies over long cables, potentially resulting in reduced headroom, lower output levels, and less reliability... So test carefully before committing!
Hugh has, unsurprisingly, summarised the issue very well.

Perhaps the most important piece is his last, almost throwaway, comment to test.

All of the comments above have effectively said "you should be OK with unbalanced cables over that short distance, but...".

Without needing to build a snake, you can test your setup out with individual cables. Connect everything up, turn up and listen - what hum/noise do you hear. Move things around - particularly around PSUs - what, if anything changes. It really isn't uncommon to find PSUs in particular inducing hum into nearby items. See if you can make that happen - then you'll recognise it if it occurs later, and be confident of what you need to do (typically moving things apart) to resolve it.

You can also try playing with long power and USB cables to confirm whether or not they'll give problems.

While it's very sensible to plan carefully and seek advice, learning by experimentation and experience can be incredibly instructive.
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Re: Live looping rig - balanced v unbalanced

Postby millipz » Thu Jul 23, 2020 11:19 pm

Really great points. I want to learn to build cables so my plan is to order an 8-channel snake and chop around the connectors to get what I want. In the meantime I can experiment with some guitar TS cables and the wall warts. Thanks for the comprehensive replies!
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