[linux-audio-user] noise from USB printer

[Pieter Palmers]

Dave Phillips wrote:
> Hi Mark :
> 
>> Ground loop problem? As a test only, what happens if you unplug power
>> on the printer, or turn the printer off?
> 
> Same noise. It stops if I pull either the power or the USB cable.
Is the noise only present when printing, or also when the printer is idle?

> 
>> If it is a ground loop issue - I did hear of this recently with a USB
>> hard drive I think - then possibly it's a cable issue or maybe you
>> could stuck a USB hub in the middle to break the loop? (Just
>> guessing!) ;-)
> 
> I tried sticking a hub between the machine and the printer, it didn't 
> reduce the noise at all. :(
That isn't very surprising as the ground will just be connected through.

What you can do to test whether it is a ground loop is interrupting the 
ground connection of the power plug (e.g. by wrapping some 
non-conductive tape around the pin). If the noise stops, you have a 
ground loop. Don't use this as a solution to your ground loop however, 
as it is probably against regulations and is also pretty unsafe 
regarding electric shocks.

If it is a ground loop, it is pretty difficult to solve. It's badly 
designed hardware. You could try to plug your printer into the same 
power outlet as the machine.

Greets,

Pieter