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Balanced ground loops
- Thread starter Ardacer
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Balanced (differential) connections are generally comprised of signal(+), signal(-), and shield (ground). This allows signal return current to flow "inside" the cable where it is shielded from external noise and such. They do not intrinsically break ground loops as the shield is connected at both ends. However, you can lift (open) the shield at one end (I lift at the load end by convention but it does not usually matter) to break a ground loop without affecting the signal path. There is an article here on ASR, somewhere, and numerous other articles online explaining how balanced connections work (including why not all "balanced" circuits are truly differential).
Some cables and components (mainly in the pro world) include a clip or switch to make it easy to lift the shield at one end.
It is also possible the ground loop is coming from some other connection, of course, so adding a balanced cable does not help.
HTH - Don
Some cables and components (mainly in the pro world) include a clip or switch to make it easy to lift the shield at one end.
It is also possible the ground loop is coming from some other connection, of course, so adding a balanced cable does not help.
HTH - Don
The shield ground and signal ground (return) are not the same in a balanced design. That means you can break the shield and not affect the signal. Breaking it at only one end means the shield is still grounded (at the other end), which maintains isolation (shielding) from external noise sources, but breaks a ground loop since the two components' grounds are no longer tied through the cable.
Can't tell, since there's no "what I'm doing" described to ponder.
OP
Ardacer
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That would perhaps explain why it still hums. Improper balanced design? If the return is earthed too, it kinda makes no sense to have it in the first place, right?
"Can't tell, since there's no "what I'm doing" described to ponder. "
Connecting a powered monitor to a pre using balanced xlr. Humms and PC noise comming through. To be specific, rokit 4 g3 and ur22mk2.
I'll try to make a custom xlr with shield disconnected on one end and see if that helps.
"Can't tell, since there's no "what I'm doing" described to ponder. "
Connecting a powered monitor to a pre using balanced xlr. Humms and PC noise comming through. To be specific, rokit 4 g3 and ur22mk2.
I'll try to make a custom xlr with shield disconnected on one end and see if that helps.
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My view is that balanced operation using screened cable won't eliminate ground loops, but can and usually does reduce their effect to the point where hum isn't noticeable.
Using unscreened twisted pairs is one way of avoiding ground loops, and this works fine for line-level signals in a benign environment. I've seen several radio stations wired entirely with UTP cable except for microphone circuits. Another way is to use transformers, and that's my preferred method if I don't know how a venue is wired, so my interface to/from their cabling to mine is through transformers.
In most situations, using modern kit which has electronically balanced IO, then screened twisted pairs do fine, and any hum loops have no noticeable effect. If they do, a couple of transformers will generally fix it.
S
Using unscreened twisted pairs is one way of avoiding ground loops, and this works fine for line-level signals in a benign environment. I've seen several radio stations wired entirely with UTP cable except for microphone circuits. Another way is to use transformers, and that's my preferred method if I don't know how a venue is wired, so my interface to/from their cabling to mine is through transformers.
In most situations, using modern kit which has electronically balanced IO, then screened twisted pairs do fine, and any hum loops have no noticeable effect. If they do, a couple of transformers will generally fix it.
S
Does it hum when only the pre and monitors are connected together?
No inputs connected to the pre?
No inputs connected to the pre?
OP
Ardacer
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I was led to believe transformers more or less degrade sound. I usually don't believe audiophoolery pseudoscience mumbojumbo but never really researched the topic fully. You'd argue they don't cause problems? What type of xformers?
No hum in that scenario. When pre connects to PC with an usb cable it gets really noisy.
Good transformers are completely transparent, and I use Sowter transformers myself, but they're not cheap, around £60 / $80 each.
As to the hum when you connect the USB cable, I think that may be due to earth leakage in the switch mode power supply. One of my laptops does that, another one doesn't. Transformers definitely stop the hum from the laptop when I have to use that one.
S
Are the pre and the PC and the monitors sharing the same electrical outlet?
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Ardacer
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They don't. I live in Europe though, so everything is wired together, no split stuff like in the states.
Those trafo's are way to expensive for what I'm trying to achive. My guess is that simply the shield and the ground is ... wait... ohmygod.jpg
I just went to check, ofcourse. Ur22mk2 has balanced trs out, so I used a balanced trs/xlr cable to connect it to the monitors. That's probably the reason, right? Shit. That also means balanced won't solve it in my particular scenario :/
Trafo's are expensive, usb isolator chips work fine with everything ecxept the ur22mk2. Kill me.
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TRS and XLR are both balanced. So an adapter like that would be fine and not cause any problems.
You've determined the problem happens when the PC is connected. Usually if the PC were connected to the same outlet as the other gear there is no or less hum (though switching supplies can be tricky about this). As an experiment you could connect to the same outlet with an extension cord and see if that makes the hum go away. Hum and computer activity noises sounds like maybe the ur22mk2 does a poor job of isolating the USB from the rest of the unit. This is just a supposition though.
If you happen to have one, you could also try a powered USB hub between PC and ur22mk2. Those will sometimes isolate noise over the USB line. Plug the hub in near the Steinberg unit if possible.
The simplest and cheapest way is to remove the screen from one end of the cable to the monitors, so if there is noise on the screen, it won't get through. This will still maintain the balance and differential connection. The next cheapest is to use a USB isolator between PC and UR22, although as the UR22 is bus powered, I'm not sure how that will work, as the power has to get through so I expect it'll depend on what sort of isolator you're using, and whether it provides onwards power. As far as I know, most don't, they just pass on the data, so you may need to look around.
S
Fitzcaraldo215
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My audio/video system is XLR connected and dead quiet, using 4 separate 20A 120 V circuits of identical length all going to the same phase on the breaker box. But, when I first connected my Media PC to the Mch DAC via USB plus HiDef TV via HDMI, there was hum, noise and garbling. The PC is in an adjoining utility room on a different house circuit.
The solution was to just run an extension cord for the PC's UPS to one of the 4 20A audio circuits. The UPS powers the PC, its monitor, my NAS and network components. That heavy duty extension cord is still there coming through a hole in the wall. No problems for years. Don't tell the electrical inspectors.
The solution was to just run an extension cord for the PC's UPS to one of the 4 20A audio circuits. The UPS powers the PC, its monitor, my NAS and network components. That heavy duty extension cord is still there coming through a hole in the wall. No problems for years. Don't tell the electrical inspectors.
I'm not familiar with Euro home wiring but I had the same issue here and solved it by lifting the ground on the PC with a 3-2 adapter.
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I do the same for the rear powered speakers in the vid set up. As the box is non-conductive I think it's okay. But it's bad safety wise. It would be a bigger concern on a desktop PC with a metal case.
What I need to do is order some of these XLR ground lift adapters for my rear two speakers. At least I think that would work.
https://www.amazon.com/Hosa-GLT-255-Female-Ground-Stopper/dp/B00FC4YPL4
If you need your PC connected that way, while still not proper, you'd be safer if the outlet is a GFCI plug. It might prevent electrocution though you could still get a nasty shock.
BTW, the AV7701 has a two pin power cord (that looks like a three pin) and only has two pins where it plugs into the chassis. I was surprised to see that in a relatively modern AV device.
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I too would NEVER EVER remove the earth from an appliance, if it's provided with a three core mains cable. The earth connection is there for a purpose, that of avoiding death by electrocution, so MUST be there.
If there's a hum loop problem, then solve it the correct way, either by disconnecting the screen from a balanced connection at one end, (or using an XLR ground-lift connector) or an isolating transformer.
S.
If there's a hum loop problem, then solve it the correct way, either by disconnecting the screen from a balanced connection at one end, (or using an XLR ground-lift connector) or an isolating transformer.
S.
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