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Advice on Ground Loops

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Advice on Ground Loops

Postby bayswater » Tue Oct 25, 2011 10:42 am

I am moving my equipment to a different room. Currently, it is all powered on a "tree" to avoid ground loops, but in the new room, I might have to use multiple outlets. Can anyone tell me whether using a different outlet for things like hard drives or digital only devices has the potential to cause ground loops? Or is it only a risk with analog audio devices? Also, IIRC, MIDI cables have the ground disconnected at one end, so I'm assuming that a device connected to other equipment only via a MIDI cable (in my case, drum pad triggers) would also not have the potential to cause a ground loop?
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Re: Advice on Ground Loops

Postby Shooshie » Tue Oct 25, 2011 1:05 pm

Anybody have a good procedure for isolating ground loops?
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Advice on Ground Loops

Postby MIDI Life Crisis » Tue Oct 25, 2011 2:14 pm

Ground lifters are the obvious quick solution. You can't force the grounds to match unless you in some way rewire the systems in question. There are audio isolation transformers for audio lines but that won't work on power lines.
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Re: Advice on Ground Loops

Postby bayswater » Tue Oct 25, 2011 2:59 pm

I know there are ways to overcome the loops. But is it possible for an all digital connection connection to give rise to the problem?
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Advice on Ground Loops

Postby MIDI Life Crisis » Tue Oct 25, 2011 3:11 pm

At some point in any audio system digital becomes analog if you intend to make the signal audible. The system ground from device to device will be shared and runs the risk of introducing hum or distortion either in playback, archive, or both. As far as I know you have to rewire the power supply to match or lift (or isolate) the loop.
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Re: Advice on Ground Loops

Postby bayswater » Tue Oct 25, 2011 5:28 pm

OK, I think that answers most of the question. So the ground levels of the attached components have to match -- it doesn't matter whether they have connected audio signals. I'll just figure out how to link everything to one 20 amp outlet with no loops.

The remaining possibility is a set of drum triggers. The trigger signal is send by MIDI to the MIDI interface, and from there to the Mac and a VI. Since the MIDI cable doesn't actually have the ground connected at both ends (I think), that shouldn't create a loop if the triggers are powered on a separate outlet. I guess I'l find out.
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Advice on Ground Loops

Postby MIDI Life Crisis » Tue Oct 25, 2011 5:31 pm

There's a good chance they could have a common ground. It really depends on the devices and cables. Lifting the ground is usually pretty safe on lower level stuff.
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Re: Advice on Ground Loops

Postby bayswater » Tue Oct 25, 2011 5:46 pm

Right. A MIDI Input it not supposed to be connected to ground, so lifting it should not be an issue.
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Re: Advice on Ground Loops

Postby Shooshie » Wed Oct 26, 2011 1:58 pm

If you're not playing your guitar next to plumbing or a refrigerator or other large metal appliance, interrupting ground isn't all bad. But it's frowned upon in technical circles since occasionally it shocks the hell out of someone -- or kills them. A tree from a single (high capacity) outlet is one way to help the situation. I'd make sure all your power strips are wired the same. That would be a pretty massive fail if they weren't, but with all this stuff coming out of emerging nations, you never know. Plug them all into each other, then use a continuity tester to make sure the circuit doesn't flip-flop from one strip to the next. (pretty unlikely that they would) Then there is each individual power supply and/or amplifier in each box you've got.

The thing about ground loops is that they do not have to indicate faulty wiring. If devices share a ground, and you've got high-powered devices and low-powered devices on the same circuit and if there is a difference in potential across the ground -- just a difference in voltage, not a mis-wiring of the circuit -- you can get a ground loop. These plague the best of electricians and audio designers, so don't feel like it's "just you." There is a lot of literature out there about this. I've plowed into some of it, but for now I'm not having too bad a problem. My stuff all feeds off of one circuit in the house, and there are no appliances on this circuit. In fact, it's pretty isolated, although my desk lamps also come off of it. Geez… we musicians also have to be computer people, electricians, AND we still have to tote all this gear? Who'd do this for a living??? :lol:

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Re: Advice on Ground Loops

Postby bayswater » Wed Oct 26, 2011 2:04 pm

I don't think there even has to be a voltage difference. Just a whole lot of wiring around a room that acts like a huge antenna picking up everything from 100 mile around seems to be enough.
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Advice on Ground Loops

Postby MIDI Life Crisis » Wed Oct 26, 2011 3:07 pm

And just to add a little more to the mix, every time I have had cable TV there was 60 cycle hum when connected to ANY grounded system. Apparently they use their own ground.
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Re: Advice on Ground Loops

Postby bayswater » Wed Oct 26, 2011 4:02 pm

In many places they share with the Telco which has it's own 48V DC power system, and the grounding is shared with the electrical utility (because they share conduits and poles.)
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Re: Advice on Ground Loops

Postby Shooshie » Wed Oct 26, 2011 5:53 pm

bayswater wrote:In many places they share with the Telco which has it's own 48V DC power system, and the grounding is shared with the electrical utility (because they share conduits and poles.)

Back in the days of rotary phones, someone brought over a little radio that had no visible source of power. Plus it was tiny, as in about the size of your thumb. That means nothing to people today, who get a full FM stereo/AM/Shortwave/Radio telescopy/GammaRay radio on a chip you can barely see with a magnifier, but then it was a big deal. The thing is, it got its power, and apparently its antenna, by clipping it onto the finger-stop of the rotary dial. It was a bare-metal piece that was connected to the phone's chassis, so it had the ground potential. Apparently, the person holding it completed the ground circuit, and you could listen to music on this thing. I've never really figured it out before, but that has to be how it worked. I mean, I knew that all appliances had a ground potential, but I could not figure out why this thing only had ONE WIRE with an alligator clip on it. Not two wires. One. That has always been a mystery to me.

Then again, the coolest radio ever was the one my grandfather gave me when I was a kid. It consisted of a base with a… oh… I'll never describe this thing. I saw one on the internet recently. I'll find a picture and post it. It's a crystal radio, and has no "power" source. I listened to it through his old antique aviation headphones. (which he'd used dozens of years before; he was a relatively well-known pioneer pilot.) That radio was gonzo! Pulling pure energy out of a rock, and listening to radio signals through it.


Image
Link

Sorry to hijack the discussion, but hey… it's all about electrical potentials!

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Re: Advice on Ground Loops

Postby bayswater » Wed Oct 26, 2011 6:09 pm

That's right Shooshie. You only really need one wire as long as you can find a path to ground and the source is connected to ground. And by ground, we mean the ground. That's how a lot of early power and telecom worked. The problem of course is that a lot of people and animals can be the conductor to ground.
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Re: Advice on Ground Loops

Postby Shooshie » Wed Oct 26, 2011 7:25 pm

Shooshie wrote:Back in the days of rotary phones, someone brought over a little radio that had no visible source of power. Plus it was tiny, as in about the size of your thumb. That means nothing to people today, who get a full FM stereo/AM/Shortwave/Radio telescopy/GammaRay radio on a chip you can barely see with a magnifier, but then it was a big deal. The thing is, it got its power, and apparently its antenna, by clipping it onto the finger-stop of the rotary dial. It was a bare-metal piece that was connected to the phone's chassis, so it had the ground potential. Apparently, the person holding it completed the ground circuit, and you could listen to music on this thing. I've never really figured it out before, but that has to be how it worked. I mean, I knew that all appliances had a ground potential, but I could not figure out why this thing only had ONE WIRE with an alligator clip on it. Not two wires. One. That has always been a mystery to me.

Then again, the coolest radio ever was the one my grandfather gave me when I was a kid. It consisted of a base with a… oh… I'll never describe this thing. I saw one on the internet recently. I'll find a picture and post it. It's a crystal radio, and has no "power" source. I listened to it through his old antique aviation headphones. (which he'd used dozens of years before; he was a relatively well-known pioneer pilot.) That radio was gonzo! Pulling pure energy out of a rock, and listening to radio signals through it.



Just had a delayed reaction epiphany. I was wondering why it only took ONE wire to power the radio mentioned above, in which an alligator clip was used to ground it onto the telephone. Where was the other lead in the circuit?

DUH!

The antenna, stupid! The electrical potential of radio waves is all around us, all the time. Just ground the antenna, and you've completed a circuit, in which radio waves already propagated from a broadcast tube with a ground are just looking for places to return to that ground. It's a very weak signal, not like listening to a transistor or tube radio with all their amplification. But it's enough to make sensitive headphones resonate electrically, responding to the tiny current by moving their diaphragms.

I got out my old crystal radio and was just staring at it, and the answer became quite obvious. Learning more about these ground loops all the time.

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