• Guys, we've spent considerable money converting the Les Paul Forum to this new XenForo platform, and we have ongoing monthly operating expenses. THE "DONATIONS" TAB IS NOW WORKING, AND WE WOULD APPRECIATE ANY DONATIONS YOU CAN MAKE TO KEEP THE LES PAUL FORUM GOING! Thank you!

Les Paul wiring issue

Gadge

Member
Joined
Jun 22, 2019
Messages
43
The reason your laptop (or any other electrical device for that matter) doesn't electrocute you is that the manufacturers have a vested interest in designing them not to do so, mainly so that they can avoid lawsuits but also so they can continue to sell you more of their devices! :) Joking aside laptops run on low voltage DC, typically 12 - 18v which is supplied either from the battery or via a mains power supply, the design of the power supply is such that the laptop itself is isolated from the mains and there is no high voltage present. Not all devices need a ground connection in order to be safe, it depends upon the design of the product.

As for your hum problem I wouldn't recommend running ground wires from the USB socket as you suggest, although this is unlikely to cause any damage or hazard it is not a recommended procedure. Without knowing the details of your setup and what you have connected to the computer it is difficult to diagnose the problem but it sounds like a ground loop of some sort. First thing to try would be to see if the problem goes away with the laptop running on it's battery and not connected to the mains. If you can let me know exactly what you have connected to the computer I might be able to help more.

Nice one, I knew that bit about the transformer thing knocking it down from 240 to 12v, this is what im curious about the bit about the design and how we know how high a voltage needs to be before it needs an earth.

Yes the laptop is quiet when running on battery and noisy with the power plug inserted.
Before reading your post I already tried the grounding plug idea and its working ok, totally silent no hum or hiss.
Heres a picture of my setup:

https://pasteboard.co/IoCGENb.png
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
673
this is what im curious about the bit about the design and how we know how high a voltage needs to be before it needs an earth.

It's actually nothing to do with the voltage but depends on the design of the appliance. There are basically 2 types of appliance, in simple terms if an appliance has exposed metal parts that could potentially become live in the event of a fault then it needs an earth connection to make it safe. If a device is designed in such a way that there are no exposed metal parts that could become live (sometimes referred to as double insulated) then an earth is not needed. When an appliance is operating normally the safety earth connection plays no part in it's operation and no current flows through it, it only does anything if a fault develops which causes some metal part of the appliance to become live, then a current would flow through the earth connection and cause the fuse or circuit breaker to blow and prevent a dangerous situation.

Going back to your hum issue, many laptop power supplies do have an earth connection, in these the earth is not needed as a safety earth but it connects the negative side of the DC supply to ground which is exactly what you are doing with your ground wire. The ground wire as you show it in your diagram will not cause any harm to anything but if you wanted a more permanent solution you could look for a suitable power supply that has an earth connection, should be easily available from eBay or other places, you would just need to make sure that it is compatible with your laptop and that it has an earth pin on the mains plug.
 

Gadge

Member
Joined
Jun 22, 2019
Messages
43
It's actually nothing to do with the voltage but depends on the design of the appliance. There are basically 2 types of appliance, in simple terms if an appliance has exposed metal parts that could potentially become live in the event of a fault then it needs an earth connection to make it safe. If a device is designed in such a way that there are no exposed metal parts that could become live (sometimes referred to as double insulated) then an earth is not needed. When an appliance is operating normally the safety earth connection plays no part in it's operation and no current flows through it, it only does anything if a fault develops which causes some metal part of the appliance to become live, then a current would flow through the earth connection and cause the fuse or circuit breaker to blow and prevent a dangerous situation.

Going back to your hum issue, many laptop power supplies do have an earth connection, in these the earth is not needed as a safety earth but it connects the negative side of the DC supply to ground which is exactly what you are doing with your ground wire. The ground wire as you show it in your diagram will not cause any harm to anything but if you wanted a more permanent solution you could look for a suitable power supply that has an earth connection, should be easily available from eBay or other places, you would just need to make sure that it is compatible with your laptop and that it has an earth pin on the mains plug.

Its a very old laptop so I will just make sure the next one is earthed and use this earth cable for now, in fact im gonna make sure everything I buy is earthed now. Thanks man.
 
Top