ground loop toolkit

[Bill Davis]

Bob,

I’m sorry, but removing the ground pin from ANY AC plug is boneheadedly STUPID. And should NEVER, EVER be recommended by anyone.

Hums are inconvenient. Shocking/Injuring/Killing people on a set is VASTLY more inconvenient.

Safe ground lift adaptors are readily available. Yeah, they cost money. But noone doing sound or sound for video should practice without them.

Sorry to be harsh. But one mistake in this area could destroy your reputation and possibly bankrupt you both professionally and personally.

Ground pins have a FUNCTION. To keep people using electricity safe and healthy.

[Bob Cole]

[Bill Davis] “Safe ground lift adaptor”

Could you name some devices that you could recommend? For both AC and XLR cables?

Thanks!

Bob C

[Bob Cole]

[Bill Davis] “I’m sorry, but removing the ground pin from ANY AC plug is boneheadedly STUPID. And should NEVER, EVER be recommended by anyone. “

I accept your view, but since I’m already publicly stupid, I thought I’d ask a dumb question.

In the service panel, I thought I saw that the neutral wire was connected to the ground. So why is there even a necessity for a separate ground wire?

Wincing as I anticipate the lash again,

Bob C (and sincerely, I do accept your judgment that removing a ground pin is stupid)

[Bill Davis]

Hosa makes a cheap one that works just fine and is under $6.
Search: Hosa GLT-255 XLR Female to XLR Male Ground Lift Hum Stopper

Or you can just go to any Guitar Center and drop $20 on one.

The cost is insignificant compared to the danger of just cutting the third pin from a grounded plug.

Oh, and the point is that THIS outlet or THAT outlet and the state of it’s wiring may or may not put you in danger at any one point. But that’s NO guarantee that in six months you won’t find yourself in a hotel where they shaved a few thousand off the building costs by hiring idiots to wire things.

Then that extension cord, or equipment IBEC power cord, or whatever that you’ve happily been using for so long that you’ve totally forgotten that you snipped the ground prong off with your dykes – that’s the cable you’ll find yourself using – while standing on a piece of carpet where a recent champagne bucket spill has you a single sodden piece of shoe leather away from a world of hurt.

Sure, 120 probably won’t kill you. Unless you’re unlucky enough to grab something live and find that your arm and hand muscles have contracted under current and you simply CAN’T let it go.

I’m not so good with that concept.

Accidents have a name because they’re a universal human experience.

Cutting ground prongs ups the odds a LOT. Plus it puts a dangerous cable out into the world where someone who’s got NO clue is free to use it to power their home built kenetic metal sculpture.

Just say no to cutting ground pins and the world is a slightly better and safer place.

[Brian Reynolds]

I always work on the assumption that on EVERY job with different powering points you will give trouble.
But NEVER, NEVER, NEVER, NEVER remove the earth on the powering side.
Have a go at this.
1. make your power feed from the same point as the rest of the AV equiptment.And run ALL of your gear from this common power.
2.Get yourself an XLR-XLR cable about 100mmm long with only pins 2 & 3 connected between the connectors.(2 needed for stereo)
3.Get a small audio transformer 1:1 ratio in a box and insert it in the line for isolation.(2 needed for stereo)
4.Make sure that any audio cables are away from power cords.

I have never known of a hum problem that cant be fixed with one or all of these steps.

The difference between Knowledge and Wisdom is… Knowledge is the knowing of facts…. Wisdom is the sensible application of good quality knowledge…

[Bob Cole]

[Brian Reynolds] “an XLR-XLR cable about 100mmm long with only pins 2 & 3 connected between the connectors.(2 needed for stereo)
3.Get a small audio transformer 1:1 ratio in a box and insert it in the line for isolation”

Thanks for the advice — more please!

When you write, “only pins 2 & 3 connected between the connectors,” do you mean simply don’t use pin 1? You don’t mean to short out 2 & 3, right?

What is a “small audio transformer 1:1 ratio?”

In your Item 1, the word “your” was linked to a post that has been deactivated. Is there something there that I should know about?

Also in Item 1, I assume you mean audio devices only from a common power point. We often need (for the lights) every circuit that is available within a 100′.

Finally, in response to Bill too, there are many practical sources in houses which have only two prongs. I assume that these are wired as I stated earlier, with the “cold” also serving as ground.

Thanks again for your help.

Bob C

[Bob Cole]

I’ve checked out some of the rec’s here. But I thought I saw something on location once that I haven’t seen online. It was an XLR hum eliminator which had a switch, so that you could either pass through all three XLR pins, or eliminate one, to get rid of the hum.

Does that sound right, and familiar? It seems better than the Ebtech HumXLR, just because if the XLR cable isn’t really the source of the hum, you don’t have to disconnect and reconnect to track it down.

Bob C

[Brian Reynolds]

Yes your right the XLR-XLR has no connection on pin 1,in one of the connectors.
The transformer I use is a 600 ohm – 600 ohm that is often found in electronics stores for telco isolation.
I tend to make most of my adaptors, some makers use switches for earth lifting.

The difference between Knowledge and Wisdom is… Knowledge is the knowing of facts…. Wisdom is the sensible application of good quality knowledge…

[Jordan Wolf]

The ground is meant to conduct electricity away from the devices we use so that, if there is a fault in the wiring (internally or externally), the parts of the gear that we touch will not become electrically charged and electrocute us. Eliminating that safety is, at best unsafe and at worst fatal.

Just say this to yourself if you think about snipping that ground prong: “What if this kills someone?”

I think that there needs to be more of a distinction between Pin-1 Lifts and Ground Lifts. One applies to audio signal, the other to potentially fatal electrical distribution.

Pin-1 Lifts can work fine – I prefer an isolation transformer myself. ProCo has some, as does Whirldwind and Jensen.

Stay safe!

Wolf
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[Bob Cole]

[Jordan Wolf] “Pin-1 Lifts can work fine – I prefer an isolation transformer”

I’m just curious – why does the Pin-1 Lift work? Why do they call a hum-inducing ground a “ground loop?”

Bob C