Karaoke Forums

Vic, can you give a link to the post you refer to? I tried to do a search but cannot find that thread.

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I can neither confirm nor deny ever having or knowing anything about nothing.... mrscott

I've seen PA's explode (amp rack caught fire), guys get electrocuted (on a construction site, he had removed the ground from a table saw) and have myself been shocked as a result of this type of thing.

A quick background on where that grounding plug came from. It was invented in the early twentieth century. In those days, with slightly less refined electrical service than most of us enjoy today, it was not uncommon to receive an electric shock when plugging a cord into an outlet. The inventor literally just got sick of getting shocked and invented a plug and receptacle that included a long round contact in addition to the two flat blades (today's NEMA-5 standard North American grounded plug). You'll notice that when you look at most grounded plugs (NEMA-5, the UK plug, etc) that the ground probe is longer than the two other contacts. This is how it was designed so that the ground connection is made first so when the other probes make electrical contact, any stray voltage can find it's way to ground through that probe rather than the person's body.

Grounded plugs have been around ever since and for good reason. It's not debatable as to their practicality or necessity, it's a proven fact. It's a safety feature, just like your seatbelts in your car, hand rails on stairs or a reserve parachute. Sure, not having any one of them doesn't mean that you absolutely will get injured, but when the situation arises where they're needed, they're your only protection against serious injury. Such is the same with your grounding connection, however not only does it protect you in a stray voltage situation, it also protects your valuable equipment.

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DJ Tony
Let It Rip Karaoke

Hi Jian

http://www.karaoke-forum.com/viewtopic. ... ht=#236215

I think this is the link. See if it works. The topic was BUZZING SOUND THROUGH SPEAKERS

Cheers

Vic in Sydney

Thanks Vic. anyone care to comment on the link?

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I can neither confirm nor deny ever having or knowing anything about nothing.... mrscott

Yep, stupid advice then too, however far from a "few years back" as was claimed....! I don't recall that thread, I definitely would have commented. Absolutely worst advice someone could give for a permanent solution.

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LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

Huh, interesting, that thread was right before I joined this board. I have to imagine had I seen that I'd have had something to say.

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DJ Tony
Let It Rip Karaoke

The talk is of breaking a ground on the DC power supply for a laptop. There is no AC going to the laptop at all, so how does that transmit itself to a microphone?

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[color=#ffff55]Mickey J.[/color]
Alas for those who never sing, but die with all their music in them.
-- Oliver Wendell Holmes, Sr.

When you have a transformer like you do for a laptop or any other DC device, one of the two conductors for the DC voltage also acts as the ground. In most cases the negative is also the ground, so this is the connection between the laptop and the earth ground.

Now that said, not all laptops have grounded power supplies. The result is that if any stray voltage comes into the laptop from an extraneous source or if for some reason the laptop has a short circuit, that voltage is going to go looking for a path to ground and might very well find it through your body.

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DJ Tony
Let It Rip Karaoke

Yes of course. Which is why transformers are usually double-insulated when you only use a two-prong power cord to a DC power supply.

But that really doesn't have much to do with causing a ground fault on a microphone or other parts of the system due to pulling the ground pin on a laptop DC power supply.

I suppose theoretically a faulty laptop power supply could connect AC to the laptop case. But that would be exceedingly unlikely, and the laptop would be unlikely to survive the experience. And it still would be difficult to show a way that a microphone user all the way on the mixer could have any deleterious effect.

Now I am fully capable of a mea culpa. Some people are fully capable of driving a truck through a pinhole, meaning that hearing they can lift any ground at all means they can lift all grounds at all times. There are people who just won't listen no matter what you say. So perhaps the best policy is to say "never clip a ground pin ever". It is clear to *me* that lifting a ground on a plastic low-voltage DC power supply is unlikely to cause a problem, but I should perhaps keep that to myself.

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[color=#ffff55]Mickey J.[/color]
Alas for those who never sing, but die with all their music in them.
-- Oliver Wendell Holmes, Sr.

Well a couple thoughts here. First, the voltage through the mic example was someone elses not mine. However, ground paths being constant throughout, if the laptop did have a short circuit situation, the ground (chassis of the laptop) is where it will bleed to. Now if the laptop itself is not grounded through it's own transformer, that voltage is going to follow your USB connection to the soundcard over that ground, then out through the shield connection of the audio cable to the mixer and now on it's ground buss. Now if the mixer is grounded, ok the voltage goes to ground there, no big deal. If not it's going to still seek a low resistance path to ground. If the only path is through the mic cable to the mic and through your body to the ground, that's where it's gonna go. Maybe unlikely and even less likely to be fatal (even less likely still if you use wireless mics ) but still possible. Additionally, as you sort of mentioned, the risk to equipment from that stray voltage exists all along that path too.

Maybe I'm just too much of a purist, but having seen the results of self appointed electricians modifying equipment, proper practice is always important to me no matter what the odds.

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DJ Tony
Let It Rip Karaoke

Now you guys have got me worried -

1. I use a grounded power strip.
2. All of my equipment is connected to the power strip.
3. My laptop is the ONLY thing without a grounding pin, but is connected to my grounded power strip.

How likely is it that something bad is going to happen?

Thanks

Vic in Sydney

Still very unlikely. You aren't really any worse off than someone whose laptop doesn't have a three-prong plug, which is very common.

But as Tony correctly points out, you don't really want to clip grounds. And we shouldn't recommend that you do, because it is too easy for someone to try and extend the situation to a point where they will clip the ground from the power strip or something bad like that.

And also, thinking about it you never quite know what is under the hood. They may have had a better reason than just using a very common power cord type.

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[color=#ffff55]Mickey J.[/color]
Alas for those who never sing, but die with all their music in them.
-- Oliver Wendell Holmes, Sr.

Vic, I wouldn't get too worried about it, of all the things you could have removed it from, the laptop is probably the least likely to have issues with stray voltage. If everything else is grounded, even if there was a stray voltage situation, it would find it's way to ground through your other equipment's ground paths. Not real likely but for future reference I would bear in mind that modifying those plugs is a bad idea and there are better ways to deal with ground loop situations.

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DJ Tony
Let It Rip Karaoke

phew... *wiping sweat off brow*

I apologize--hadn't had the chance to see if a new cable or USB card would fix the problem. will keep you posted

The amps from the usb ports alone can kill you.....

switched the cable and same problem---it turns out it is the AC adapter to the laptop---when it runs on battery ---quiet as a mouse --plug it in to a power strip or directly into the wall STATIC AND NOISE. I guess it could be the actual socket I am using in my basement???---I'll try try this laptop at my gig FRIDAY and see if I get the noise...oh well

Anything else on that circuit - not just that outlet but the entire circuit itself (many outlets may be on the same circuit - you probably know that, just for others that may not) - flourescent lights, anything with motors, etc...

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LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

I have seen laptops where the charging circuit is close to the sound card and causes interference when it is plugged in. Do you have an external USB soundcard you can try?

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DJ Tony
Let It Rip Karaoke

And you tried unplugging the TV and that made no difference?

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[color=#ffff55]Mickey J.[/color]
Alas for those who never sing, but die with all their music in them.
-- Oliver Wendell Holmes, Sr.