Noise heard through Sub when laptop plugged in...

[JRace]

When I have my laptop plugged i I can hear a quiet noise coming from the subwoofer. This happens with both a Cerwin Vega powered sub and with my passive shiva/butkicker BK1000 setup.

The sound was not audible at all through a Paradigm Ultracube 10 powered sub.
As well the sound is louder if I increase the subwoofers level control.

When I disconnect the laptop powers supply the sound goes away.
The sound occurs when the laptop is working hard or accessing the HD.
I have tried connecting both power supplies through a power bar, both directly into the same outlet, and both on different oultes (same fuse though).
I have fixed the cable tv induced ground loop hum, and this is stll present.

Any ideas on where to start?

[brucek]

Does the noise go away when you use a 'cheater adapter' on the laptop power supply?

If so, it's a simple groundloop..........

brucek

[Wayne A. Pflughaupt]

brucek can probably speak to this better than I can, but I’d suspect the computer’s power supply. In general, they aren’t known for clean power. There may be some residual AC artifacts not being adequately filtered or rectified.

Worse case, using an outboard USB sound card should solve the problem.

Regards,
Wayne

[JRace]

I havnt located a cheater plug yet.
If it is a groundloop, and ideas on how to fix?


Wayne: I am running the audio through a Soundblaster external USB and coax.
No diff between that and the onboard audio.

[Wayne A. Pflughaupt]

Perhaps we should back the boat up and start from scratch.

A good place to start would be to give us a description of the system you’re talking about. In your first post you mentioned “plugging in” the laptop, but didn’t tell us what you were plugging it into. You also mentioned “HD” and “cable TV.” So I’m really confused about what we’re dealing with here. I’m not sure if you have some kind of home theater PC rig, or if you’re merely trying to connect a laptop to a regular HT system.

Regards,
Wayne

[JRace]

It is a laptop running an external usb (digital coax) to a Marantz reciever.
Video is sent thru the VGA out into a Projector.
The only device going into the laptop is an external USB harddrive.
The subwoofer is conected via the reciever's sub/LFE ouput.
We have internet only through the CATV - no televison.
I eliminated the ground loop hum created by the CATV a year ago, no hum heard through any speakers.

When I refered to "plugging in" the laptop I meant the power supply. The sound heard through the sub goes away when I am on battery power.

I meant Hard Drive - not High Def!! I can see the confusion now ...
When the laptop is idle (no cpu draw and not accessing the hard drive) the sound goes away. If I move the mouse the sound returns.

The sound heard is not a HUM - more of a click/clack/tick/tock...if taht makes any sense!

Thanks for the help, I may have a cheater plug by the end of the day.

[Otto]

So it's related to the drive? I believe that the drive could go into some type of power saving mode when you are on battery, and may only be used when it's needed -- it will probably be idle when it's not actively doing something. However, when plugged in with full power, the drive may take liberties to search around for problem areas or in other ways "take care of itself." That's normal drive behavior for 2.5" drive.

I doubt that a cheater plug will help you in this case, but it may. Does your laptop have a ground pin on its AC plug? I know neither of mine do.

[Wayne A. Pflughaupt]

I doubt a cheater plug will help either, although it can’t hurt to try. At least it would verify if its a ground loop problem. (Never been able to figure out why laptop power supplies have grounded plugs anyway...)

Since it all starts when the power supply is plugged in, I’m still suspicious of it.

Anyway you can change out the coaxial digital cable to the Marantz with an optical?

Regards,
Wayne

[JRace]

Problem still happens with optical...no change.
(The soundblaster external USB does both optical and coax).

The laptop has a three pronged power cord and I have no cheater plug to try at the moment.

I am having the same problem !!!!
I bought this ampli with 2 speakers ... and I also bought the creative xmod device (sound going through the usb port) ... I can hear noise through the speakers ...
even with the external usb device !!!
so I bought better cables, a power bar that has filtering.
and im still having the problem ...
naturally when i unplug the laptop's power the noise goes away ... any help ???