> Hi there, Martin. > > The standard approach is to use an audio isolation transformer. I > have had very good success with issues such as what you are describing. > > Shameless plug: my company sells little isolation transformer modules > for not much money. These use a semi-custom transformer from > Datatronics and really do work very well. I think that cost is > around Can $25 in singles (soon to increase due to supplier cost > increases) plus shipping. > > > > Let me know if you want to try this out. I'll arrange to send one to > you and you can either pay for it or return it as you see fit. > > dwayne I agree that the simplest way to do this would be with an audio transformer. The next simplest way would be with a differential amplifier. I'd use two conductor (twisted pair) shielded cable. At the unbalanced output, the - conductor is connected to chassis. The + conductor is connected to the unbalanced "hot" line. At the differential amplifier (or transformer), the + and - leads go to the + and - inputs of the differential amplifier (or to the transformer primary). I'd still tie the grounds on each piece of equipment together (shield tied to chassis at each end) to minimize the common mode voltage on the differential pair. There will be some shield current, but it should not induce anything into the differential pair. If the grounds are not tied together, there can be substantial common mode voltage that is difficult for the differential amplifier or transformer to reject. Harold (I still have my Western Electric 111C audio transformer) --=20 FCC Rules Updated Daily at http://www.hallikainen.com Not sent from an iPhone. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .