I made a recording of a 2-LP set before ever listening to it, and after mucho processing, I listened and discovered that it was corrupted by large amounts of ground noise. Bleh. I had to throw them out and re-record.
After much searching I discovered that the power supply from my Dell laptop was the culprit. Moving the turntable cables away from the PS relieved the noise. Moving them back increased it. Wrapping the cable around the power supply amplified the noise tremendously.
The noise consisted of peaks about 30db above the noise floor at 60hz and 180hz, many peaks in the 20db range from 200-10khz, and a huge mass of +20db harmonics centered at about 13khz and 18khz. Not subtle at all.
This throws a major wrench into my whole way of thinking about balanced turntable connections. I was under the impression that a well-shielded balanced cable is fairly immune to EMI of this nature; clearly I'm mistaken.
Microphone and pro audio connections have the same issues; I'll need to research how sensitive they are supposed to be to this sort of thing before I consider making cabling/equipment changes.
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