Karaoke Forums

Hey folks, I'm looking for thoughts on this, hopefully someone will see the obvious solution that I haven't tried yet or at least I'll get some fresh ideas. There's a bar that I play at on a very irregular basis. They have a big screen TV that they want me to display the lyrics on, no problem, I have the PC to TV EZ adapter so it gives me an RCA to send to the TV and the VGA goes to singers' monitor.

This all works great except for one little problem, I get a ground loop through the RCA cable. The TV is plugged into one power source and all my equipment into another and apparently the ground is carrying all the way through the computer, the audio connections through to the mixer where the loop rears it's ugly head as that wonderful 60Hz hum. So I'm trying to come up with a good way to isolate this and so far the only solution I have found is not one that I like.

For now, I've been using a 3-prong adapter as a ground lift for all my gear (can't convince the bar owner to do so on his TV so I'm stuck). This is the only thing that completely eliminates it by ensuring only one path to ground. However, I don't trust the sheild of that RCA cable being sufficient as an electrical ground if truly needed. So my last gig their I decided to just put a gate on the offending channel to take out the hum. Well that works for the audio, however the ground loop causes interference with the TV and so the picture had the 60 cycle bars scrolling through it.

So I'm looking for thoughts on how I can isolate the TV's ground (coming through the RCA) from my equipment and keep my equipment properly grounded. I had thought about connectong the laptop to the mixer through a stereo DI with a ground lift (right now it's a 1/8 trs to dual 1/4 TS Y-Cable direct), but I'm not 100% certain this would work either. I've tried looking for some kind of ground lift that could be added to the video signal chain but so far have had no luck finding anything. I'll gotta say I'm pretty amazed that the ground from that RCA perpetuates itself all the way through the USB or VGA (Not sure which yet) interface on the laptop all the way through the audio connection on the internal soundcard and to the console.

Let me know your thoughts.

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DJ Tony
Let It Rip Karaoke

Will the bar owner allow you to plug the tv into the same source as your other equipment via extension cord? That sounds like the easiest solution, but I could be wrong. You're much more tech saavy than me, so I'm sure you know better than I do, just thought that sounded like an easy solution.

Srnitynow

Is it coming from the satellite/cable connection? If it is HDMI, or you could get a quick-disconnect connector for another cable type, you could disconnect the satellite at the same time you connect the RCA.

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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.

I tried rca video ground isolators from MCM electronics. They didn't really work. The hum went away (at least to an un-noticeable background level) when I switched to JBL EON 315s from Peavey PR15Ps.

Jonn

That's an interesting thought. I hadn't even considered that the loop may not be from the electrical ground but rather from the grounded cable connection. I'll definitely have to experiment with that.

srnitynow as far as plugging the TV into the same source, I believe that doing that would correct it for sure (unless of course the loop turns out to be through the CATV connection), however given the way the TV is installed and where I'm not sure it would be feasible to do that. It's pretty tight up against the wall and the power is on the far side of the TV that I can't reach. I'll at least take a look next time I'm there and see what I can determine.

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DJ Tony
Let It Rip Karaoke

Disconnect the bar tv from the other video source.

edit....ah see it was suggested. I used to have this problem with cable systems.

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

Hmmm. Some laptops have two prong US power adaptors that aren't made with one prong slightly wider than the other to assure proper phase. If your laptop is one of these, unplug the power adaptor and see if the problem goes away. Then if it does, rotate the plug 180 degrees and plug it back in to see if the problem stays gone.

You could also try one of these . . .

http://www.radioshack.com/product/index ... Id=2062214

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Dave's not here.

This helped me out after the bar went to satellites. http://www.ebtechaudio.com/he-2des.html
I had to use this because the bar had sat receivers plugged into the TV that we split off to.

Tell the bar owner its ok because you have a "flux capacitor" built into your system.

But really, why would he not go for that. At one of my gigs I've tried everything to get rid of the hum and the good ole 3 prong plug seems to be the only fix.

good luck, Mojo

Because he understands enough about electricity to know that there are safety concerns surrounding not having equipment grounded, but doesn't know enough to understand what they are and how it wouldn't impact him if I did this with his TV.

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DJ Tony
Let It Rip Karaoke

[quote="letitrip @ November 5th 2009, 10:10 am"][quote="DJMojo @ Thu Nov 05, 2009 3:18 am"][quote]For now, I've been using a 3-prong adapter as a ground lift for all my gear (can't convince the bar owner to do so on his TV so I'm stuck). [/quote]

Tell the bar owner its ok because you have a "flux capacitor" built into your system.

But really, why would he not go for that. At one of my gigs I've tried everything to get rid of the hum and the good ole 3 prong plug seems to be the only fix.

good luck, Mojo[/quote]

Because he understands enough about electricity to know that there are safety concerns surrounding not having equipment grounded, but doesn't know enough to understand what they are and how it wouldn't impact him if I did this with his TV.[/quote]

Just bring in a pair of good cutters and cut off the third prong on his TV cord and plug it back in. The guy will never notice the change until he replaces the TV in the future.

Bruce, that is dangerous and illegal. I guess you didn't read letitrip's earlier post when he said a ground lift adapter on his audio rig can solve the problem, but he does not want to do that because it's ... dangerous and illegal. So why would he want to make an unauthorized, dangerous, and illegal modification to a TV he doesn't own?!

I wish I knew the answer to this problem, too. One of my friends has the same issue at a bar he works 6 nights a week. The only way I was able to get rid of the noise was to use a wireless TV transmitter/receiver system to electrically isolate the laptop from the bar TVs. All that did was help, not solve, the problem because the building ground is full of garbage too.

I would do what you thought about earlier, letitrip, and try a common power source for that TV and your audio system; but again I think it won't help because of the cable or satellite system.

What about a switch for the TV's coax input? If it's not connected to the cable / satellite when you are using it, because the switch is in the "karaoke" position, this might help?

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Jeff Wheeler, moonlight DJ/KJ

Yeah I think what I'm gonna do the next time I'm there is first try disconnecting the coax from the cable input and see if that takes care of it. If so I'll have to come up with a more permanent solution (possibly a switchbox like you suggest althought I'd need to make sure that it isolates the ground).

The interesting thing here is the first time I played the bar, I didn't have this issue. However that night we also had a big storm that knocked out the cable in the bar for most of the night. The next time I came in, I had this issue. Would be interesting if something they did repairing the cable that night led to this.

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DJ Tony
Let It Rip Karaoke

From my experience, almost none do. A DPMT switch is rare, indeed. That's why I recommended a quick disconnect.

If it's a HD signal, you might get lucky and have HDMI which would be a snap to deal with.

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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.

http://en.wikipedia.org/wiki/Sheath_current_filter apparently what you need is called a "Sheath current filter." Amazingly I could only find some on eBay and e-tailers I've never heard of before. By what they have on Wikipedia, it seems you could easily make your own with a plastic box to hold the bare wire, a cheap capacitor, and some solder.

Maybe this is a common feature in "Home Theater" or A/V power strips with "filtered" coax in/out, and they just don't advertise it with that terminology?

It might be worth buying a fancy Monster A/V power strip from BestBuy or another store with a good return policy. If it doesn't solve the problem, take it back. If it does, well, don't feel bad for spending $50 - $100 on a Monster product if it fixes the problem.

You might try posting this question on the LAB Lounge or Basement and see if you get pointers to a commercial product from some of the smart A/V guys.

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Jeff Wheeler, moonlight DJ/KJ

Perhaps the answer is as simple as one of these--> http://www.ebtechaudio.com/humxdes.html

Lonnie reccomended this to me in an earlier thread and I got one and it does indeed work. You can do a search and find them for less than half of the MSRP.

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Music speaks to the heart in ways words cannot express.

Not to over simplify things, but why not use a wireless video transmitter and isolate it completely. They're fairly cheap and nice to use when you don't have easy cable access to a TV.

I have a 2.4GHz wireless video transmitter that I could setup, however that to me would be almost a last resort thing. I'd have to find a place to put the transmitter and the receiver where line of site will not be blocked. Also, the bar has a cordless phone and I don't know what frequency it operates on, but from experience if it is a 2.4GHz phone it will interfere. It is a possibility that I'll keep in my list of things to try next time, but as I said, there's a lot of other potential solutions I'd like to try first.

RLC, I did look at that device and I may try it out. However, since it can only support equipment with up to a 6A draw, I'd have to put it on the TV rather than on my equipment. I'm pretty sure my amp alone would draw 6A.

I was also looking last night at a way to build a ground lift into an RCA cable. I found instructions for doing it for RCA audio, I'd just need to make sure it would work for a video cable as well, I'm not sure what frequencies travel over an RCA video cable.

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DJ Tony
Let It Rip Karaoke

Rip: You said that the problem came up after an electrical storm, and the cable had been knocked out.

A couple of things that I would check out are

1. Make sure that the ground at the TV is actually working, if you are getting a ground loop through the cable back through your equipment maybe the ground for the TV is not actually there and was being provided by the cable they fixed and now that cable is ungrounded.

2. Hook your cable up to the TV and check to see if there are any voltages on that cable before you plug it into you equipment. Voltages coming down the cable could ruin your equipment.

another solution:
Buy a 75-Ohm Coax Combiner-Splitter and a "Matching Transformer". The 75-Ohm Coax Combiner/Splitter converts the impedance from 75 ohms to 300 ohms and the "Matching Transformer" converts the impedance from 300 ohms to 75 ohms. Both parts connected together will act as a "poor man's" isolation transformer.
(taken from wikipedia so I didn't have to type it all out). I have used this when a neighbor complained that my Ham Radio signal was getting into his TV, and although it wasn't my equipment I helped keep the peace by doing this.

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I like everyone when I first meet them. If you don't like me that's not my problem it's YOURS!
A stranger is a friend you haven't met yet

I say go with the wireless system and give us the number of the bar. We'll keep calling and see if we can knock the TV off-line.