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<blockquote data-quote="Scott Helmke" data-source="post: 6858" data-attributes="member: 96">Here&#039;s an interesting thing I ran across a couple weeks ago.&nbsp; I did a service call to a big church with the praise band, to troubleshoot hum problems in their monitor wedges.&nbsp; We (me and the house tech) went through all the usual things.&nbsp; Finally found that the hum occurred between the monitor position and the amps, and could be mostly removed with isolation transformers.However, it also turned out that the 20 amp circuit to monitor world had a rather high neutral to ground voltage, a bit more than 3 volts.&nbsp; None of the other dedicated audio power had anything that bad.&nbsp; Now here&#039;s the &quot;aha!&quot; moment.&nbsp; They had a pretty full load on that circuit, big old Yamaha M3000 console plus a bunch of UHF-R, some analog outboard, and power amp for cue wedge.&nbsp; So there was measurable line loss, even though they weren&#039;t overloaded on the circuit.&nbsp; We borrowed a big heavy extension cord from the maintenance guy and used it to power the monitor console from a random outlet backstage... and the hum was drastically reduced.&nbsp; We started turning off wireless and the cue amp, and the hum dropped even further.Now here&#039;s the interesting part.&nbsp; Electricity travels in a loop, Kirchhoff&#039;s Law, symmetry, etc.&nbsp; So line loss happens not only on the hot wire, but equally on the neutral wire.&nbsp; As the hot wire drops, the neutral *rises*.&nbsp; &nbsp; And we all know that a high neutral to ground voltage is usually found right alongside system hum and noise.&nbsp; Which means that we really want to send thick wire and extra circuits on that long FOH run, to minimize line loss.</blockquote>

[QUOTE="Scott Helmke, post: 6858, member: 96"] Here's an interesting thing I ran across a couple weeks ago. I did a service call to a big church with the praise band, to troubleshoot hum problems in their monitor wedges. We (me and the house tech) went through all the usual things. Finally found that the hum occurred between the monitor position and the amps, and could be mostly removed with isolation transformers. However, it also turned out that the 20 amp circuit to monitor world had a rather high neutral to ground voltage, a bit more than 3 volts. None of the other dedicated audio power had anything that bad. Now here's the "aha!" moment. They had a pretty full load on that circuit, big old Yamaha M3000 console plus a bunch of UHF-R, some analog outboard, and power amp for cue wedge. So there was measurable line loss, even though they weren't overloaded on the circuit. We borrowed a big heavy extension cord from the maintenance guy and used it to power the monitor console from a random outlet backstage... and the hum was drastically reduced. We started turning off wireless and the cue amp, and the hum dropped even further. Now here's the interesting part. Electricity travels in a loop, Kirchhoff's Law, symmetry, etc. So line loss happens not only on the hot wire, but equally on the neutral wire. As the hot wire drops, the neutral *rises*. And we all know that a high neutral to ground voltage is usually found right alongside system hum and noise. Which means that we really want to send thick wire and extra circuits on that long FOH run, to minimize line loss. [/QUOTE]

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