To resolve this I took home an old Otari DAT machine from work that didn't work properly. The DAT has an in & out SP-DIF which makes it ideal to connect to the PulsarII for use as an external D to A converter.
Result:
The input into my desk is now as clean as a whistle. I can't quite believe that I have been living with this noise (minimal as it was) whilst that DAT machine was sitting in a cupboard idle. Doh!
So, the lesson here is: Check out all those old bits of kit lying around.

<font size=-1>[ This Message was edited by: mgranger on 2003-10-09 04:32 ]</font>