Electrical cabling question for stage setup

[Mojo34]

Hi -

I ran into a problem a stage setup problem the other day with my band: I had electrical hum that I couldn't get rid of!

My usual pedalboard does not make noise, at least none that I hear at home or in practice. The usual "ground-lift" button tricks were not working at all, cables all plugged in, and no loose ends. The last pedal in the chain is a Two Notes Cab M+. I didn't have a ton of time to troubleshoot, so I tried XLS from the Genzler Maggelan preamp and I didn't have the buzz. But the sound without the Cab simulation was not what I wanted, so I plugged in my trusty Tech 21 Acoustic FlyRig and played my heart out with no buzz.

We had two electrical cables coming in for power: our layout had all the amplification, monitors, and PA system on one line, and *most* of the lights on the other. The guitar player had actually plugged some LED lighting into his power strip... which we figured out was causing buzzing for the piano on that same side of the stage! We separated that out and their noise went away.

So my question is this: IS IT COMMON KNOWLEDGE THAT YOU HAVE TO RUN LIGHTS ON A DIFFERENT CIRCUIT FROM INSTRUMENTS?

Thanks! Got a big show tomorrow and am looking forward to any answers the hive mind might provide.

 

[Slevage]

For starters—hum and buzz are two different issues. Hum is generally “conducted” noise, often ground loop or polarity. Buzz is generally emitted noise. It’s possible that the line and neutral on one of the circuits on your problem gig were reversed.

 

[Mojo34]

Interesting, thank you. But how to troubleshoot? All the plugs are power strips and extension cables, with the ground pin (round French plugs).
However, two of my pedals are only 2 prongs (old Carl Martin pedals) and could be plugged in either way. Could that maybe be the issue you are talking about? Note: we are on 220 V in France.

 

[Mojo34]

It's possible that my pedals are the real problem. I've turned on the noise gate in the Cab M, with the absolute minimum setting and it seems to resolve hum that I have here just using an active speaker.
I'll try that tomorrow, but also will bring my backup preamp.

 

[DanAdams]

You need a circuit tester in your guitar case. you can get one at any hardware store.
What was the deal with the show? A club? A random room with extention cords? an outdoor thing?

I've heard that you are less likely to get ground loops or other electrical gremlins if the circuits that you are pulling from are on the same phase.
Most US panels are two phase. Hopefully someone more knowledgable can chime in with wisdom on this.
knowing what each musician's rig amp draw could be helpful in the future.

 

[Mojo34]

The show was an outdoor gig with extension chords. We had two main chords, one intended for lights, one intended for all the rest. I personally think we are pulling too much on the everything-else line (PA, amplified speakers, monitors, pedalboards (for DI), one small tube amp, and a piano. The question is also whether lights should necessarily be on their own line.

 

[poochiecheeks]

i would be interested to hear how the electrical system works in france. but i think a loud florescent light would be picked up by single coil pickups or unbalanced instrument cables regardless of what circuit its on
you have 220v @ 50hz there?

 

[Slevage]

You need a circuit tester in your guitar case. you can get one at any hardware store.
What was the deal with the show? A club? A random room with extention cords? an outdoor thing?
View attachment 7525089
I've heard that you are less likely to get ground loops or other electrical gremlins if the circuits that you are pulling from are on the same phase.
Most US panels are two phase. Hopefully someone more knowledgable can chime in with wisdom on this.
knowing what each musician's rig amp draw could be helpful in the future.

Most US panels are split phase (different than 2 phase, which doesn’t exist), though many many years ago, there were 2 phase motors running on 3 phase systems.

 

[klyph]

Just because they ran two different cables, from two different outlets, doesn’t necessarily mean two different circuits. Battery power might be your only fool proof solution.

 

[cannedsardines]

You need a circuit tester in your guitar case. you can get one at any hardware store.
What was the deal with the show? A club? A random room with extention cords? an outdoor thing?
View attachment 7525089
I've heard that you are less likely to get ground loops or other electrical gremlins if the circuits that you are pulling from are on the same phase.
Most US panels are two phase. Hopefully someone more knowledgable can chime in with wisdom on this.
knowing what each musician's rig amp draw could be helpful in the future.

If you plug one of these in and learn that the circuit is wired incorrectly, what would you do? E.g. hot and neutral reversed, floating ground?

 

[DanAdams]

If you plug one of these in and learn that the circuit is wired incorrectly, what would you do? E.g. hot and neutral reversed, floating ground?

I would try to use another recepticle and/or extension cord that the tester could confirm was wired correctly.
I would inform the venue that their electrical system is faulty and potentialy dangerous.
I would then not have to wonder what the issue was, or be fearful that the problem was inside my or the band's equipment.

There is a notable list of musicians who have received dangerous shocks, and even been killed by faulty wiring.
I'll bet that many of us have been stung on the lips by a SM58. I have been.

 

[Jefenator]

When you know you have two different breakers, it might not be the worst idea to isolate lights & sound.
Last night I wanted to the lights off a different generator. But one of the organizers took the second one to use elsewhere, so back to plan B.
My main concern was running down the battery. Hum never came up as an issue. (And turns out, we didn't run out of power, either.)
I've actually shared power with various smaller LED setups (yard lights and/or just a few stage cans) quite a few times now & never had an issue yet. Fluorescent neon sings & dimmers are a whole different story of course. Fortunately, I see less & less of those.

 

[Engle]

I had issues with LED stage lights creating noise in the PA. I found using Furman SS-6B-PRO power bars for the audio equipment worked. I'm in Canada, so obviously those wouldn't work for you, but maybe there is a similar product for Europe.

 

[Wasnex]

The noise can come from nearby cables, certain type of lights, etc. It can also be from noise riding on top of the AC, ground loops, etc. Noise is a very complex problem and it's not always possible to figure out a solution. Do the best you can.

 

[Mike Caldwell]

As mentioned earlier the type of noise can help where to start looking.
Something as simple as an unbalanced cable laying in and around a couple of wall wart power supplies can pick up noise or said type power
supply that is still working but yet failing and putting out noise RF or through the power to the device.

A simple XLR cable that has pin 1 tied to the outer shell can cause all kinds of strange noise problems......or none at all!
Hunting down a noise in a PA system can be challenging and kind of fun at the same time.....or not some days.

 

[Slevage]

If you plug one of these in and learn that the circuit is wired incorrectly, what would you do? E.g. hot and neutral reversed, floating ground?

Look for a different source if L and N are swapped. If there is an open G, using an extension cord with it’s own GFCI is a safe alternative.

 

[BassNugget]

Years ago, when I worked at Berklee, I learned not to run power and audio cables parallel to one other. If you have to cross them, do it at 90 degrees and you can tape the crossing down so it doesn't shift.

This solved a lot of hum and noise problems.

 

[Mike Caldwell]

Years ago, when I worked at Berklee, I learned not to run power and audio cables parallel to one other. If you have to cross them, do it at 90 degrees and you can tape the crossing down so it doesn't shift.

This solved a lot of hum and noise problems.

That could cause issues and even more so if the AC power cable is carrying a big current load, that said I lost count of the times I ran the snake to FOH and laying right along beside it was the power cable for FOH and that could be upwards to 150 feet. I don't miss moving that case with the snake in it and that was a short snake by some standards!

 

[JamesGrant]

Yep - very common to have separate lighting power and sound power cables.
And very common to keep lighting power from dimmer to fixtures well away from audio signal cables.

I once did a regular gig in a newly opened bar who had terrible trouble with bands and mains noise. I was the booking agent for the venue. I went in and troubleshooted early on morning at delivery and stocking time. Turns out the kitchen was on the same ring as the stage power sockets and amplifiers/soundweb… a kitchen full of fridges, freezers, etc etc.

Got their sparky down there that week and moved the stage onto its own breaker and the kitchen onto its intended phase. No more problems.

 

[4Mal]

I always try for lights on one circuit and audio on another. With modern LED though, probably it's just my habit from the old days... One thing I do in my lighting rig. No signal cable on the floor. Wireless dmx to the tree with all the tree's fixtures locally hard wired. That may help,with noise. It sure makes the setup and tear down faster.