Hi,

just want to share a solution, which might be useful for others, too. There are some threads in this forum about hearing "my computer working" and other noises when connecting the analog output expansion to other external equipment.

Some users were able to minimize the noises by changing BIOS settings for energy saving modes and other (E1ST, C1E, C3/C6/C7, C1/C2/C7, Virtualization technology, CPU thermal monitor). In my case, none of these did work. The device manager (Win XP) showed, that the HDSP9632 used the same IRQ as one of the USB ports and an IDE (hard drive) device. So my thought was, maybe the noise is caused be an interrupt conflict. By setting the BIOS option "On-Chip SATA" to "Non-Combined" instead of "Enhanced" a different IRQ became assigned to the IDE device and I disabled the USB port. This reduced some of the noises just a little bit, but still was far away from being a solution.

In my case the solution was "old school": the cause of the noise seemed to be a ground loop between my computer and the external eqipment (which has unsymmetrical inputs). Inserting a ground isolator between the analog outputs of the AO4S and the inputs of the external equipment removed the computer noise as well as the "hum" to a level, where it is not anymore perceptible (compared to an audio signal played back at the same level). I did some research because I wanted an affordable and easy solution (it's just for the monitoring headphone amp when recording - no hi-end solution needed here). Finally i found passive, ready to use ground isolators in the field of car-hifi. I tried the FGA-40 by Monacor and it works very well for my setup. Only the connectors are of the wrong type (RCA) - back to the soldering iron.

I am not saying this is *the* solution, but if nothing else works, it is worth a try.

Finn