Device to remove a ground loop hum?

JohnW63

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I've used various devices to try and remove the ground loop 60hz hum and not all of them work. I have a teacher that has a powered speaker connected with an XLR cable and a plugged-in device that feeds it. He hasn't told me what that is exactly. They get plugged into different outlets and get the hum. I found this device online that seems to get good reviews.


It does it by working on the power line from one of the two devices rather than the audio connection between the devices. That would not filter out tone from the speaker, I would guess.

Has anyone used this device or knows of ones that work well and you can recommend them?
 

GAD

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An isolation transformer will solve your problem if it's a ground loop. I don't think the HumX is an isolation transformer given its size, and I seem to recall some concerns with the fact that they're not UL listed, but aside from those concerns, a lot of people swear by them.
 

JohnW63

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I figured an isolation transfomer would work, but when I did a quick Google of the internets, this one came up a lot.

I am pretty sure it is because the teacher, are you ready for this, ...used an old power cord and broke the ground prong off and didn't have a hum when he fired it back up.
 

GAD

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I figured an isolation transfomer would work, but when I did a quick Google of the internets, this one came up a lot.

I am pretty sure it is because the teacher, are you ready for this, ...used an old power cord and broke the ground prong off and didn't have a hum when he fired it back up.
Not surprising. Ground is one of those things that is kind of non-intuitive for most people. Until you've been shocked by a live chassis or got RF burns from an improperly grounded ham station (assuming you're not an EE or has been trained by someone who knows better), grounding is just this nebulous thing we know is good but we're not sure why.

Cutting off the ground plug breaks the ground loop. Isn't that the goal? :)
 

Rocky

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Cutting off the ground plug breaks the ground loop. Isn't that the goal? :)
😲
I know you're joking, but...

The proper way to do it if you're daisy chaining two amps is to cut the shield on the instrument cable connecting the two amps at one end. That way the path to ground is through the mains on both amps.

I believe the Hum-X uses diodes between the different legs to filter out the hum. There's a fairly extensive exploration of it here: https://www.thegearpage.net/board/index.php?threads/diy-hum-x-5-ground-loop-fix-how-to.1691481/
 

GAD

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😲
I know you're joking, but...

The proper way to do it if you're daisy chaining two amps is to cut the shield on the instrument cable connecting the two amps at one end. That way the path to ground is through the mains on both amps.

I believe the Hum-X uses diodes between the different legs to filter out the hum. There's a fairly extensive exploration of it here: https://www.thegearpage.net/board/index.php?threads/diy-hum-x-5-ground-loop-fix-how-to.1691481/
The proper way to do it is to fix the damn power in the first place. I never get far with that argument all the way up to Fortune100 CEOs, though.
 

Rocky

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The proper way to do it is to fix the damn power in the first place. I never get far with that argument all the way up to Fortune100 CEOs, though.

True, but as long as bar owners let regulars pay their tabs off in trade, there will be sketchy power in clubs. When possible, I try to have people all plug into the same outlet, to minimize the chance of reversed polarity/ground issues between band members and the PA. But I don't play big places with big PA either.
 

Nuuska

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I'll play . . .

First I assume you are talking about a system, that is quiet in one place, but not somewhere else.

The idea of grounding of a large sound system is somewhat similar to a tree - like birch. Each leave must have one - and only one - path to ground.

And before going deeper - the system MUST ALWAYS BE GROUNDED ! ! !

Let's start simple - one guitar connected into two amps. Plug guitar into first amp - and have the signal of first amp taken from line output of first amp into second amp. We have a triangle earth wiring - sides of the triangle = 1 amp power cord ground wire - 2 second amp power cord ground wire - 3 interconnecting cable ground wire. They make a loop. And because there is this omnipresent electric field - there is some of that field fowing through that loop generating hum.

There are at least three solutions - simple one is to use the ground, lift adaptor in the power cord of the SECOND amp. This way your guitar strings will be grounded via first amp. Drawback is, that if you need to use the second amp separately or in a pinch plug into that - you must first remove the adaptor plug off the power chord. But in case of ground failure combined with some other failure in first amp you are in shaky situation at least.

Second solution is that if you take the signal of the first amp from a line output, you can use a cable or box with signal transformer, that provides galvanic isolation between amps. In this case both amps power cords must be grounded.

Third solution - you may have a floor board that has external "wall wart" PSU - and with any luck there might be two separate outputs w possible ground switches for signal - I have never seen one yet, but they might exist. At least you have the last output of your pedal board - and that is low-impedance - thus capable of having a box with two transformers - primaries parallel - secondaries each feeding their own output - or a transformer w single primary + two separate secondary windings feeding their receiving amps.

I'm only scratching surface here - but I hope you get the picture - a tree with each leave connected to ground - but only one way.
 

steve488

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I have to go with GAD on this one. Changing the symptom does not resolve the problem..... and yes there may be one of those EE's related to ma someplace in the past :)
 

Guildedagain

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JohnW63

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The teacher in question is on an assignment to go around to all the schools showing off cool science stuff to the kids in the gymnasiums/ cafeterias. I think he has a mixer or PA system and then plugs a second powered speaker to the output to cover the large rooms. The speaker is powered by the nearest plug and the gear at the head end to it's nearest plug. The schools are various ages. From the late 1950s to 2008. What quality of electrical quality he may find at each place is a roll of the dice.

If the most expeditious way to kill the hum is to use one of the above hum busters , then I will suggest it.

We often use these Tripp-Lite ISOBAR strips on our equipment, but I don't think it would isolate the grounds to reduce the hum.
 

GAD

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The teacher in question is on an assignment to go around to all the schools showing off cool science stuff to the kids in the gymnasiums/ cafeterias. I think he has a mixer or PA system and then plugs a second powered speaker to the output to cover the large rooms. The speaker is powered by the nearest plug and the gear at the head end to it's nearest plug. The schools are various ages. From the late 1950s to 2008. What quality of electrical quality he may find at each place is a roll of the dice.

If the most expeditious way to kill the hum is to use one of the above hum busters , then I will suggest it.

We often use these Tripp-Lite ISOBAR strips on our equipment, but I don't think it would isolate the grounds to reduce the hum.
Nice strips. I use one in my home lab.

That makes sense. I’ve worked in old schools and seen some frightening things. I remember doing sound for one of the kid’s shows in the late 00s. This was an elementary school and when they brought me to the sound stuff it was just a giant knot of cables, power cords, and the off piece of PA gear jutting out from the knot.

Luckily the power at that school wasn’t bad. Now, the “new school” in town that went live around 2000 was a nightmare because of constant cost overruns. Sure it looked nice and new, but go into any of the wiring closets and I’d just back out slowely and say, “Nope.”
 

Nuuska

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The teacher should absolutely bring his own extension cord and use single wall outlet for everything. The way he is doing it now is asking for hum to appear. Those two outlets might be wired to different fuses - and who knows how far to fuse box. Might be in other end of building. And they might even be wired to different fuseboxes with different feed - thus enlargening the ground loop up to hundreds of yards.

If his system runs quiet in any one place wired into single wall outlet - then all he needs to do on the road is to carry his own cables and find one decent well grounded outlet.

When I travel with bands - I never ever let them use the nearest wall outlet for anything. I have my own wire harness that covers entire backline and frontline. They plug into that and no hum. More work to do - but less hassle - plus most importantly - it is electrically safe for everybody and their gear.
 

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The teacher should absolutely bring his own extension cord and use single wall outlet for everything. The way he is doing it now is asking for hum to appear. Those two outlets might be wired to different fuses - and who knows how far to fuse box. Might be in other end of building. And they might even be wired to different fuseboxes with different feed - thus enlargening the ground loop up to hundreds of yards.

If his system runs quiet in any one place wired into single wall outlet - then all he needs to do on the road is to carry his own cables and find one decent well grounded outlet.

When I travel with bands - I never ever let them use the nearest wall outlet for anything. I have my own wire harness that covers entire backline and frontline. They plug into that and no hum. More work to do - but less hassle - plus most importantly - it is electrically safe for everybody and their gear.
Yep. All your better PA companies will connect a sub panel direct to a venue's power supply (often w/ assistance from the in house electrician), and supply several quad AC outlet boxes on stage, all set up before the band begins to load their gear.
 

JohnW63

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I've offered him the surge strip and extension cord solution if he wants to try them.

I always like to be helpful with this teacher as he has got the coolest stuff and does a good job with the kids. He has a doctorate in Aeronautics, so I guess he is a rocket scientist. Before COVID he got one of our high schools to host a NASA downlink from the space station and our department handled all the sound gear and hookups. It's on the NASA channel somewhere. He also has a room where he has 4 projectors in the corners of the room and projects 3D images in the center of the room. Of course, one is the DeathStar. I think it's probably a 4-5 foot diameter image. Gary needs one of these setups.
 
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