Phil Leigh;548980 Wrote: > Never seen this on an SMPS (linear has transformer phasing to consider > which is a real effect - usually on a linear, reversing the > live/neutral will/won't alter the radiated EMI field of the > transformer). Also, the Touch SMPS has no earth... do you mean leakage > to the DC ground?
Yes, its leakage between the AC line and the "DC GND" going to the Touch. The DC GND is connected to the "shield" of the analog outs which connect to the "GND" of the box the interconnects connect to. There will always be some parasitic capacitance between the DC GND and the prongs of the plug, this allows ac current to flow between the mains and the DC GND of the device. Its usually pretty small but its still there. In most power supplies, even SMPS, the parasitic capacitance from DC GND to the two prongs is usually somewhat different. AND because in most countries one side of the main is a "neutral" (grounded somewhere in the house) there is asymmetry in the system. The ground current flowing through the interconnect shield will vary depending on which way the plug is inserted. The current flowing through the interconnect shield will induce a small voltage across the shield, and since at the far end of the cable the input circuit sees the voltage between the center pin and the shield, the noise voltage developed across the shield is added the the signal you want and gets amplified along with it. You can get rid of this affect by using balanced interconnects because the signal the receiver sees has nothing to do with the voltage on the shield. I'm pretty sure this is why people like balanced better, its not that the balanced system picks up less noise on the signal wires, but because its immune to ground current noise on the shield. This is just my paraphrase of whats really happening. There are several papers out on the net that go into detail about all this. I don't remember exactly where they are off the top of my head. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=78959 _______________________________________________ Touch mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/touch
