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Need Your Help. High-mid pitched buzz, suspect: laptop PSU?

Hi, I seek your help/advise as I am stuck in a classical situation. "It worked fine so far but today when I need it ..."

My setup. :

Recording path: Mics >> Mackie 1640 >> Firewire >> HP NX 7400 Laptop
Monitoring path: Mics >> Mackie 1640 >> Aux 1, 2, 3, 4 >> 4 channel headphone amp.

What happens:

All connected as above, the laptop runs on batteries there is no issue.
Jittery noise comes up as soon as I connect power supply to the laptop.
If I power up the mixing desk (connected via firewire with a laptop) the noise becomes even louder.

Interestingly the noise is loud even with the volume knob all the way down on the headphone amplifier...


Tried various electrical sockets.
Connected both laptop, mixer and headphone amp to the same switch board and then to 3 different sockets via extension leads. Tried different cables. No luck.

Anyone has any idea what is going on and how to sort this out?


Pro Audio Guest Wed, 02/13/2008 - 07:06

It does look so indeed ...
I use stock power supply that came with this laptop, 3 wires with earth, sure.

Interestingly there is no noise from the notebook headphone socket. The noise was passed only via firewire.

I reduced problem by using a different firewire cable. Same lenght though and both cable work fine in terms of data transfer.

Strange. Anyone who might have technical explanation is welcome to share it here...

Btw. do you know of any manufacturer that offers laptop power supplies that are decent? Seems like HP are cutting corners on power supplies big time.

JoeH Wed, 02/13/2008 - 10:15
What laptop are you using? I still suspect there's something potentially weird with the Mackie Onyx firewire interface & overall grounding. (I have three ONYX systems with FW; don't get me wrong, I like them a lot).

BUT, I was once the poster child for weirdness with my ONYX and Sony Vaio laptop a while back, with a very weird/odd problem. (It's over on the Mackie forums ad nauseum...) Mine was weird spikes that occured in the AUDIO domain, whenever I had the battery connected to the laptop.

Worked fine with the battery alone, worked fine with the AC adapter alone, but with both connected, troubles began. Turns out it was the charging circuit; every three minutes, i'm guessing the machine would attempt to charge the battery or at least poll it, and that's where we finally traced the spike, which showed up in the audio path (and printed to the audio files. ) Once I removed the battery while using AC, it was fine. (Went absolutely NUTS trying to find it, beforehand....sigh....)

I've long since upgraded my VAIO to a newer model, and the problems went away. Still, I have always suspected there's something odd with the ground path & the FW connection in the ONYX FW adapter. Just a theory, but who knows....?