USB hum/noise

[Sholarios]

Hi, all.

I got in trouble buying EMU 0404 USB and Alesis M1Active 520 and attaching them to my laptop (Acer Aspire 5672wlmi). The notebook produce huge hum + hiss + other noises as much time it is connected to AC source. All the headphones i had until now didn't make it evident. When the laptop is on its own battery, nothing of this sort appears, the sound is clear (even if i am not at all satisfied by the hiss of the monitors, which exists by default when you turn the knob of GAIN close to maximum, without any source of signal).
The plug is grounded, so this is not the solution. The AC converter produces the noises and i can't find any solution to cut it.
I am thinking in buying a new notebook, but what should i buy? I don't want to hear such parazite noises coming from the USB.

Any kind of help would be greately received.

[charlesE]

It sounds like a ground-loop problem. The EMU 0404 has it's own power-supply so it's probably not a power-noise issue. You could try getting an audio isolation transformer, like this one:
The Source By Circuit City : Cables - RCA Audio - GROUND LOOP ISOLATOR ADAPTER

But it will distort the audio somewhat, you can find some that are much better than that one, it's just an example.

You probably didn't hear it with headphones because it's your amp that's creating the ground loop with your laptop. You could also try using a power cord that doesn't connect the third prong on your amp to the wall, but try that at your own risk. It is a violation of a handful of safety regulations that are there to ensure that you won't get electrocuted if the mains inside the amp short out to the case. I suggest just trying that as a test; if at all, and if it eliminates the issue going to your local Audio Shop and asking them for a more permanent ground-loop elimination product (there are many available).

You could also try plugging your amp and laptop into the same power-bar, that may help.