Buzz in PA system

[JKT]

NNNNNNOOOOOOOOO! Don't ever tell anyone to do that again, please. There are WAY to many products to deal with ground issues without eliminating the AC ground of ANY equipment to ever recommend something like that.

Oh Please. I didn't tell anyone to stick their tongue in a lightbulb socket.
Tell me you've never had to get power from a non three prong outlet. If you haven't, then you obviously have never gigged outside your bedroom.

Is it better to be plugged in to a nice comfy, three prong all the time?
Sure. Will the dudes amp explode if tries to isolate a hum problem? Probably not. If there is a real risk, you should probably not be using that power source anyway.

JKT

 

[lindseyp]

Where can you find a two-prong source outside your bedroom in the U.S.? Where they would let you plug a rig in, I mean.

 

[JustDavid]

Oh Please. I didn't tell anyone to stick their tongue in a lightbulb socket.

Literally, no you didn't. But what you did advise can be just as deadly. Yes, deadly.

Tell me you've never had to get power from a non three prong outlet. If you haven't, then you obviously have never gigged outside your bedroom.

No I never have, & yes I gig a fair amount. We ALWAYS plug into properly-wired outlets (at least they are when I test them, & the defective ones I tape over with red tape) ALL sound into a distro I've made (& had verified by a licensed electrician) that also has full ground fault protection.

I can get behind using a ground lift INTELLIGENTLY & SAFELY; what you recommend is neither safe nor intelligent. I'd use it as a troubleshooting step ONLY, making sure everyone is hands-off gear, & do it briefly to prove the issue or not. But I do not recommend that to everyone.


Would you hand an electrician your bass & expect him to do a decent job playing it? Then how is a bassist playing Electrician any different?

 

[Alaska Bass]

Oh Please. I didn't tell anyone to stick their tongue in a lightbulb socket.
Tell me you've never had to get power from a non three prong outlet. If you haven't, then you obviously have never gigged outside your bedroom.

Is it better to be plugged in to a nice comfy, three prong all the time?
Sure. Will the dudes amp explode if tries to isolate a hum problem? Probably not. If there is a real risk, you should probably not be using that power source anyway.

JKT

Technically when you plug your gear into an improperly wired system, your bass can very easily become the socket, so actually you are telling them to.

Does Barker Basses really sponsor you? With the bad rep and liability you impose, I am suprised by that.

The very fact that you are offered a groundless power source at a gig should tell you that the sites power is suspect.

And "gigging" in front of a few thousand of my closest friends is nothing new for me, but nice try. Grow up and quit giving bad information to others. It might just save a life one day.

 

[GregShadoan]

The OP's buzz could be coming from any number of places. In a perfect world, there would be no AC ground loops. But since we all live in the real world, I think we could all agree, that improperly installed AC circuits exsist. As to the issue of AC ground lifts, I would like to make it VEERY clear that these should ONLY be used as a troubleshooting tool. Not a FIX. If an AC gound lift fixes an AC ground loop issue, then you should not use said outlet, but continue to troubleshoot until a safe clean properly installed AC outlet can be found. Preferrably from the Audio AC distro. If the term AC distro is a mystrey to you, step away from the outlet. AC power will KILL you. Please use extreme caution. Please consult with a certified licened bonded electrian to solve any AC problem.

 

[JustDavid]

First off, peace bro!! Let's try to move this forward for people.

The very fact that you are offered a groundless power source at a gig should tell you that the sites power is suspect.

I feel I should urge ALL to purchase an outlet tester & keep it in their kit. Roughly $5.00, the kind with 3 lights (2 yellow, 1 red), available at any hardware store.

The tester will immediately tell you if an outlet is wired correctly. If it isn't, don't use it.

There are levels & levels of Stagecraft when it comes to power feeds, but please at least observe that first & basic level.

 

[GregShadoan]

First off, peace bro!! Let's try to move this forward for people.



I feel I should urge ALL to purchase an outlet tester & keep it in their kit. Roughly $5.00, the kind with 3 lights (2 yellow, 1 red), available at any hardware store.

The tester will immediately tell you if an outlet is wired correctly. If it isn't, don't use it.

There are levels & levels of Stagecraft when it comes to power feeds, but please at least observe that first & basic level.

These devices, although very helpful, (often referred to as mouse'ers) will not identify a ground "loop". Everyone should have one. A mouse'er that is

 

[JKT]

Where can you find a two-prong source outside your bedroom in the U.S.? Where they would let you plug a rig in, I mean.

I have seen it too many times to count

JKT

 

[JKT]

Technically when you plug your gear into an improperly wired system, your bass can very easily become the socket, so actually you are telling them to.

Does Barker Basses really sponsor you? With the bad rep and liability you impose, I am suprised by that.

The very fact that you are offered a groundless power source at a gig should tell you that the sites power is suspect.

And "gigging" in front of a few thousand of my closest friends is nothing new for me, but nice try. Grow up and quit giving bad information to others. It might just save a life one day.

I have to say, this is slightly an over-reaction and exaggeration. Temporarily groundlifting and sticking your tongue in a light socket are never gonna be the same thing and anyone adhering to that is just an alarmist nut. And I didn't have to qualify as an electrician to enter into an endorsement deal.

And you sir, are getting a little nasty with absolutely no call to. Whats the deal? Too cold up there?

I also never recommended the procedure beyond troubleshooting the OP's hum problem. If you want to disagree fine. We can disagree. Why don't you save your personal attacks for another forum?

 

[cdawzrd]

First of all, I'm guessing the bassist is referring to his VOLUME knob as DRIVE for some reason.

Second of all, to the OP: Does the bass hum with ONE 1/4" cable straight from the bass into the mixing board, standing right next to it? Try another 1/4" cable that you haven't tried before if so, to make sure it isn't the cable.

Does it hum when you plug that same cable into the DI box, then an XLR cable from the DI box into the board? Try a different cable, and a different XLR cable. Try both positions of the ground lift switch for all cables.

If it hums at the first step, it's probably the bass's pickups. Step two, it's probably the DI. If the bass only hums when you introduce the amp into the equation, then the only thing I can think of is that the DI is not properly lifting the ground and creating a ground loop. Again, this points to a new DI as the easiest solution. Maybe try borrowing a DI from someone to make sure that fixes the problem.

 

[JKT]

I can't remember, did anybody suggest groundlifting at the amp AC yet?

JKT

Notice how I didn't say everything should be fine now?

Notice how I just suggested to groundlift the amp?

Remember the OP mentioning he had a hum problem?

If he has a hum problem, them we can assume he is already plugged in to said power source.

This isn't someting I would do in a chicken coop, but oddly, I have never gigged in a chicken coop. Close mind you, but not actually in a chicken coop.

You'll have to excuse me. I have been a working musician for over 3 decades. You pick it, I have played there. And most of the time for people who don't always care what my opinion of the power and wiring are, but who do care that music happens when they expect it. Call me a rebel, call me a daredevil, but yes kids, I have lifted to find/stop a buzz here and there in my travels. Implying that it is akin to sticking your tongue or finger in a hot socket or that one is flirting with death because of it is IMO a little over the top. Yes, bad things can happen in this old world. But I'm way more scared these days of actually driving to the gig.

 

[JackANSI]

You guys do know that 'ground lift' on a properly designed amp (if its UL listed, its wired like this) doesn't actually lift the ground from the chassis right?

It just breaks the connection of the earth ground to the audio ground...

Most amps also are incapable of delivering more current (from the wall socket, worst case) than their input impedence will allow from their input jack to ground. You'll feel this as something like a 9v on the tongue when you bring your lips up to a grounded microphone. Now tube amps will give you a bit more of a jolt, but usually no more than an 18V battery.

I don't recommend lifting your whole amp, just open up a XLR cable (on the end that plugs into your rig) and snip the wire at pin 1 (ground) and the sheild if its not the ground also.. There is your ground lift DI cable. You and your amp are still grounded, but the ground loop buzz should diminish greatly. If you leave the other end (PA end) ground and sheilds intact, the sheild is still going reject noise relative to the system that matters (PA).

Then proceed to

 

[JustDavid]

JKT, I read you the same way Alaska did. True, you didn't say permanently, but you didn't say it should be done only temporarily as a troubleshooting step nor urge caution about the hazards groundlifting can create.

 

[JustDavid]

These devices, although very helpful, (often referred to as mouse'ers) will not identify a ground "loop". Everyone should have one. A mouse'er that is

True; ground loop detection'd be quite a bit more than $5

Towards that end, there's one Behringer product I love!! Their cable tester will verify shields, & trap some intermittents.

 

[Alaska Bass]

I have to say, this is slightly an over-reaction and exaggeration. Temporarily groundlifting and sticking your tongue in a light socket are never gonna be the same thing and anyone adhering to that is just an alarmist nut. And I didn't have to qualify as an electrician to enter into an endorsement deal.

And you sir, are getting a little nasty with absolutely no call to. Whats the deal? Too cold up there?

I also never recommended the procedure beyond troubleshooting the OP's hum problem. If you want to disagree fine. We can disagree. Why don't you save your personal attacks for another forum?

You never said anything about temporarily doing anything. The way you phrased your comment could easily be construed to mean removing the ground pin on the 120 volt plug to your amplifier. This is unsafe and can lead to death, yes death.

Perhaps I was not quite as polite as I should have been; it actually warmed up to -27* F today, so hopefully I will be less "nasty".

 

[Alaska Bass]

You guys do know that 'ground lift' on a properly designed amp (if its UL listed, its wired like this) doesn't actually lift the ground from the chassis right?

It just breaks the connection of the earth ground to the audio ground...

Most amps also are incapable of delivering more current (from the wall socket, worst case) than their input impedence will allow from their input jack to ground. You'll feel this as something like a 9v on the tongue when you bring your lips up to a grounded microphone. Now tube amps will give you a bit more of a jolt, but usually no more than an 18V battery.

I don't recommend lifting your whole amp, just open up a XLR cable (on the end that plugs into your rig) and snip the wire at pin 1 (ground) and the sheild if its not the ground also.. There is your ground lift DI cable. You and your amp are still grounded, but the ground loop buzz should diminish greatly. If you leave the other end (PA end) ground and sheilds intact, the sheild is still going reject noise relative to the system that matters (PA).

Then proceed to

The comment was "groundlifting at the amp AC". This means removing the ground pin on a 3 pin AC power cord (whether directly or through a 3 pin to 2 pin adapter). It is not safe, and opens up tremendous liability (the guitar player tells the bass player to do it, or even worse does it himself/the bass player gets electrocuted/who goes to jail?).

Isolating the audio ground from the chassis ground is a very different creature, and one that still is not necessarily good, this can actually increase the chance of noise in the system.

I agree that a telescoping SHIELD on a balanced cable can eliminate the potential for ground loops if done correctly.

 

[JackANSI]

Still not going to get more current to go through the input jack the impedence will allow.

The preacher got whacked by the direct earth ground of the plumbing system, reduced skin resistance due to the water he was waist deep in, and some other device somewhere in the church that shared the same electrical ground as the audio system, and was in fault of that on the neutral side. Had to be something low resistance, like a motor on a fridge or a light fixture.

 

[JustDavid]

Good point about ground lift on XLRs. & a 'ground-lift XLR' cable is a good troubleshooting tool to have in the kit.

Most amps also are incapable of delivering more current (from the wall socket, worst case) than their input impedence will allow from their input jack to ground. You'll feel this as something like a 9v on the tongue when you bring your lips up to a grounded microphone. Now tube amps will give you a bit more of a jolt, but usually no more than an 18V battery.

No, no, no. DANGEROUS advice.

I'll agree for a newer model amp functioning properly. But broken amps frequently act in ways they aren't supposed to, & some of them can be lethal.

no more than 18 V from a tube amp

 

[JackANSI]

whatever

 

[Alaska Bass]

Still not going to get more current to go through the input jack the impedence will allow.

The preacher got whacked by the direct earth ground of the plumbing system, reduced skin resistance due to the water he was waist deep in, and some other device somewhere in the church that shared the same electrical ground as the audio system, and was in fault of that on the neutral side. Had to be something low resistance, like a motor on a fridge or a light fixture.

That logic is flawed. Depending upon the breakers used (GFCI or Arc-fault or regular) and if they are functioning correctly, you could receive an electrical shock (even if it is a short duration) that is much higher then the rated capacity of the circuit breaker. The conductor size and impedence built into the cable that is attached will limit to some extent the amperage that will flow through the cable but this in no way means you can't get shocked or killed with a 120v 20A circuit malfunctioning while you are providing your body as the contact between power and earth ground (ever read about someone electrocuting themselves in a bathtub?).

Properly designed equipment that is properly wired will limit the exposure to this almost completely, HOWEVER, we are talking about equipment that is already suspect (remember the buzz?).

As for the pastor, your logic is flawed as well. He was in the water with no problem until he touched the microphone (which made him the contact between an improperly grounded/electrically charged audio system and earth ground which came from the water in the baptismal font). The electrical discharge went through his body and several hundred people got to watch him get electrocuted. If there was power on the neutral leg of the building power due to miswiring, proper audio wiring proceedures would have shown that, and the situation could have been remedied.