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Junior Varsity
Complete the DC circuit?
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<blockquote data-quote="Jay Barracato" data-source="post: 5426" data-attributes="member: 24"><p>I had one of those throw up your hands at someone elses poor decisions shows the other night.</p><p></p><p>At a local restaurant/bar, they have a minimal system that was anything but professionally installed. I went in there about 3 weeks ago with a band and at least got everything they had in a reasonable working configuration. All the power was being drawn from a single edison on the wall through a "power conditioner" on the amp rack. This is one of those restaurants that converts into a bar right in front of your eyes and they don't expect anything to come out of the system until the first song of the bands performance, so I was a little limited to how much tweaking I could do. I did fix a couple of things like subgroups are not necessarily for subs, and it is not necessary to patch everything into everything on the board (there was more effects in the monitors than signal).</p><p></p><p>I went back with the same band last week and as soon as we setup, the singer tells me his mic is shocking him. I shutdown and start checking it out. It turns out someone had replaced the extension cord feeding the whole rig with one of those two wire lamp extension cords, and since the three prong from the rack wouldn't fit into it, they had pulled out the safety ground prong.</p><p></p><p>Wouldn't you know that this was the one night I didn't have a single of my good extension cords in the car?</p><p></p><p>A little checking showed the problem was the global phantom power on the mixer. Which led me to start thinking about interfacing AC and DC equipment. I know that the phantom is DC fed along pin 2 and pin 3 with the ground on pin 1. What I am not sure of is the connection inside the mixer between the ground of the XLR jacks and the safety ground of the entire mixer. Why would breaking the ground connection on the AC feed open the DC phantom power circuit? It seems strange to turn the safety ground into a current carrying wire, even if it is only DC. If I were to measure between the safety ground wire of the cable feeding the rack and the ground of the wall jack, should I be able to see that 48 V DC? It seems to me that this DC current could end up all sorts of places you wouldn't want it.</p></blockquote><p></p>
[QUOTE="Jay Barracato, post: 5426, member: 24"] I had one of those throw up your hands at someone elses poor decisions shows the other night. At a local restaurant/bar, they have a minimal system that was anything but professionally installed. I went in there about 3 weeks ago with a band and at least got everything they had in a reasonable working configuration. All the power was being drawn from a single edison on the wall through a "power conditioner" on the amp rack. This is one of those restaurants that converts into a bar right in front of your eyes and they don't expect anything to come out of the system until the first song of the bands performance, so I was a little limited to how much tweaking I could do. I did fix a couple of things like subgroups are not necessarily for subs, and it is not necessary to patch everything into everything on the board (there was more effects in the monitors than signal). I went back with the same band last week and as soon as we setup, the singer tells me his mic is shocking him. I shutdown and start checking it out. It turns out someone had replaced the extension cord feeding the whole rig with one of those two wire lamp extension cords, and since the three prong from the rack wouldn't fit into it, they had pulled out the safety ground prong. Wouldn't you know that this was the one night I didn't have a single of my good extension cords in the car? A little checking showed the problem was the global phantom power on the mixer. Which led me to start thinking about interfacing AC and DC equipment. I know that the phantom is DC fed along pin 2 and pin 3 with the ground on pin 1. What I am not sure of is the connection inside the mixer between the ground of the XLR jacks and the safety ground of the entire mixer. Why would breaking the ground connection on the AC feed open the DC phantom power circuit? It seems strange to turn the safety ground into a current carrying wire, even if it is only DC. If I were to measure between the safety ground wire of the cable feeding the rack and the ground of the wall jack, should I be able to see that 48 V DC? It seems to me that this DC current could end up all sorts of places you wouldn't want it. [/QUOTE]
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Complete the DC circuit?
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