Hi,

I seek the wisdom of this list.

I have set up a Digital Audio Recording system.

I have connected one set of line outputs from a small fixed-installation
house PA system (built around a Mackie board) into the line inputs of a
Tascam Digital Audio Workstation (DAW, for short). This workstation is
located in a small closet with the sound system. It is basically a high
quality sound blaster, with tapedeck like transport switches for control,
connected through USB to the PC.

The sound system has myriad inputs and outputs which I could elaborate on,
but it would take a long time.

It connects to a Dell P4-1.6GHz approx. 30 feet distant, in another room. I
have used a USB extender by B&B Electronics to make the USB connection to
the DAW, and I have a run-of-the-mill stereo audio cable with 1/8" stereo
phone plugs to carry the line out signal to the Dell powered speaker system
in the room with the PC, thus giving the ability to monitor the program
content at the PC while recording.

It can be controlled at the DAW, or at the PC.

Now, the problem: When the flourescent lights are on in a room which is not
located in proximity to either the PC or the Sound system, I get 60Hz hum
ONLY at the DAW's line output, not anywhere in the sound system. This shows
up both on the recorded content on the PC, and in the powered speaker
system's output, but not on the mains of the PA system.

Switch the lights off, and the hum goes away.

I have tried powering the remote PC, powered speaker system and all it's
peripherals from an extension cord coming from the sound system closet.

I have also tried a stereo audio isolation transformer on the line going
back to the PC, and tried an AC "hum eliminator" from Radio Shack on the
supply of the PC and powered speaker system. No joy.

The cable carrying the line signal back to the powered speaker system runs
through the ceiling, above some acoustic ceiling tiles. I examined it's path
and do not see any AC wiring in it's direct (within 2 feet) vicinity.

I plan to try a separate cable running along the floor in place of the cable
in the ceiling to send the line signal back to the powered speakers.

I also plan to try moving the PC and speakers right next to the DAW and
eliminate the USB extender and use short cables, to see if this affects it.

I also have a circuit for creating a balanced, high voltage signal to
transmit the audio and at the other end converting it back again, which as
of now is my last resort.

Another clue, if I run the line output of a LCD multimedia projector into a
line input on the mixing console through some permanently installed cable in
the room, I also get this symptom, but only when these lights are on.

Does anyone have any suggestions as to how else I might eliminate the hum?

Thanks,
Mark

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