As explained in the previous FAQ, the vast majority of laptops use a switched mode power
supply with a twin-core mains cable, so that there is no direct earth (ground) connection.
However, this isn't always the case, since some US users have found they can cure audio
interference problems with certain laptops by using a 'three-prong to two-prong adapter',
which effectively means they are disconnecting their laptop PSU earth connection from the
Some Dell models fall into this category including the Latitude
D-Family and the Inspiron 8200, 8500, and 8600, and I've found lots of disgruntled users
on Dell's forums complaining about various background noises.
You should be able to
tell fairly easily which category your laptop falls into, since two-core mains cable is
usually has a flat oval shape, and may even use a two-pin plug at the PSU end. If it has a
round profile, or uses a three-pin plug at the PSU end, then your laptop motherboard
ground connections may already be connected to earth, and as soon as you plug other
earthed audio gear into it you may create the classic ground loop.
this ground loop 'fix' can also be employed by UK users by removing the moulded mains plug
and wiring another by hand and leaving the earth wire disconnected, this may seriously
compromise your safety if any of the laptop exterior metalwork is also connected to earth.
If temporarily lifting the mains earth cures your problem, the safe solution is to buy a
line-level DI box or make up a special set of audio cables, as explained in the previous
Incidentally, while researching this FAQ I also came across details of
problems with audio interference during CD playback with the Dell Inspiron 8500 model, due
to drive noise being passed on the internal analog CD audio lines. This has apparently
been cured with a BIOS update.