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Your laptop doesn't do anything clever, it's just not earthed. My suggestion of lifting the ground doesn't do anything unsafe, it just emulates what you're doing when you're plugging it directly into your laptop by not earthing that connection.
Ground hum occurs when you have a potential difference between the points at which your system is connected to the earth. If you have a single earthing point you will not have a ground hum because there's no ground loop - you can't have a potential difference when you have a single earth connection. If you're using shielded phono leads and these are plugged into your MiniDSP then there will be a route to ground to whatever it is they're grounding to on the other end. Lifting the ground on a wall plug which is only connected to your MiniDSP will not be unsafe because it's exactly the same as plugging it into your laptop.
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There's lots of stuff like this around https://hifimediy.com/product/usb-isolator/ not sure whether they are proven or snake oil though.
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Exactly this!
The phono cable is already 'carrying' ground from the amp. If then you connect that phono cable to something connected to ground, you are creating a ground loop!
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Removing ground from something isn't advisable but doesn't mean something bad will definitely happen. Ground is there more as a safety measure. Removing ground to check if that is the source of an issue, if done carefully, can be hardly labelled as dangerous.
If by removing the ground the hum is gone, that solves the issue and kind of proves there was a ground loop. Btw when you break a ground loop everything is still grounded! -
when you break a ground loop everything is still grounded!
But the earth loop impedance may be higher than planned, which does a couple of things. First, it means a fault from live to the casework will expose the user to a higher potential, and second the fault current will be reduced so protective devices (fuse, circuit breaker) will open slower or maybe not at all.
TL;DR: Never cut the earth connection where it is part of a mains voltage circuit.
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If that was the case removing the computer from the outlet and running it on battery would sort the problem?
On a guitar I guess even the person holding it can work as a 'ground loop'? specially if bare foot... :D
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Yes, the guitarist can create a hum but usually when you touch the strings the opposite happens.
Your computer is not really running from the mains, it's charging and powering the battery. I would never have said your computer has no earth potential, even if the power supply has no earth the case is connected to earth. So all the time you only have one source of earth there is no hum, introduce another different source of earth and it creates a hum.
I'm not going to try and give you a definitive answer to why without having a close look at the equipment involved and running some tests but the problem is the potential difference between 2 pieces of equipment and it's a nightmare in sound engineering because different designers have different approaches.
Almost all systems have some noise, it's a question of how much gain you apply to it. Guitars/Mic Inputs/Phono Stages are all small amplifiers providing a lot of gain so they are a common source of noise.
Just to say I've built phono amps, amps and all kinds of micro electronics but don't pretend to understand them in any great depth. I'm also a qualified electrician but when I have the same problem as you I leave the thing plugged into the usb port.
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yeah, ground hum is an absolute pain in the arse. I'm an electrical design engineer - for consumer products we build to standards to pass safety certification so as long as you're within certain tolerances it's 'fine'. For things like audio equipment, however, fine for a safety standard doesn't necessarily cut it for audio quality / interoperability.
This is why I suggested lifting the ground on a power supply connecting to the 5v usb port. It's a low voltage circuit which has already been identified as being able to fix the problem. Saves the hours of ground hum problem solving you'd have to do plus it's not risking any safety problems.
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It all gets too complicated to provide a simple answer doesn't it. I was reading the first few posts thinking 'great, someone on here might know what to do!'. I'm no wiser after the answers.
If you indelibly marked the adaptor as having the earth removed and for use only by a competent person for the specific purpose maybe no one could complain. It's still a socket that is expected to have an earth though. Most people don't realise the earth (or cpc) and neutral are joined in the consumer unit.
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This is why I suggested a USB plug with a plastic ground pin first - it's a consumer unit which is only expected to be used with low voltage stuff rather than an extension cord which you might forget about.
The combined PE + N system in the UK is a real problem when you're designing stuff with high loads for outside use. If you have a broken PEN line somewhere it means that your PE line effectively becomes an extension of your neutral return. If you've got a metal casing (think heavy duty catering equipment in a gazebo) which will be grounded internally to the PE - you've now got a fridge in a gazebo carrying mains current through its easily graspable metal handle.
If only our grid hadn't been built on the cheap and they just ran a standalone PE.
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I don't think so. I mean, if you specifically want LS50s, get 'em.
One thing I will say is if you have CA floorstanders and move to LS50s you're losing a lot of lower frequencies. So I'd be cautious of that. The lack of low end is one of the main reasons I returned my Meta's.
Not sure what CA you have but the SX-80 freq response is: 40Hz – 20kHz
And the Meta's: 79 Hz - 28 kHz
Those are very different sets of speakers...
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Audiophiles hifi appreciation thread old and new
Posted by
@coppiThat
Agreed, I don't want to remove safety earthing. The phono leads are new (and expensive) shielding should be excellent on them.
How does the laptop usb port lift the ground? Surely there's something cheap and similar which does the trick?