Dmills Posted February 16, 2009 Share Posted February 16, 2009 National motorhome show. People travel in theirs, and stay over night on a car park....... Staying in a motorhome on a car park. In February.Okaaayyy, I can see this, now how much do the organisers pay people to do this thing? Sleeping in the back of a van, in February, in a car park, sounds like some sort of low budget tour gone pearshaped. In fact I am sure I remember this one from my late teens! Regards, Dan. Link to comment Share on other sites More sharing options...
Rob_Beech Posted February 16, 2009 Share Posted February 16, 2009 The money isn't brilliant but its a small show, that I can do on my own and it pays for kit (just about) , transport, hotel, and 5 days engineering. You must have misunderstood, I was saying whilst I have that stuff in my van, I've paid for a hotel. I'm not sleeping in a vehicle like the punters do. Link to comment Share on other sites More sharing options...
J Pearce Posted February 16, 2009 Share Posted February 16, 2009 It could be said that you're not sleeping at the hotel either, as you're still on TBR at 2.30am :blink: However, this is all getting rather off topic and frivolous for a topic entitled Ground loops in a multiphase amp rack. Link to comment Share on other sites More sharing options...
Dmills Posted February 16, 2009 Share Posted February 16, 2009 The solution is to run the mains for FOH from the stage and then there is just the single earth point on stage.Can't do that? Got to run FOH from local power? Use an mains isolating transformer at FOH to break the ground reference. Go to whatever lengths are necessary to keep and maintain a single earth point, it saves so much time in the long run :blink:Well yes, that works, but in a largish installed system it is horribly fragile (Think feeds to media rooms, monitors in the lobby, paging and show relay, maybe an OB feed.....), personally I would rather just fix the racks so they handle balanced lines properly, then you do not have to worry about it. I don't like a system where some numpty plugging in a video deck in another part of the building can start things humming where I am (Seen it at a previous venue, it was nasty and if I ever get my paws on the installer.... ). I really dislike the whole 'technical earth' approach, it is a pain in the arse and IME does not really work. Circulating currents in the screens should not be able to couple to the electronics reference grounds full stop. If they can (say because pin one goes to ground via a trace that goes three times around the mic pre), then THAT is the problem, not a few hundred mA of induced screen current. Now SCIN is real, and can be an issue, but it is so far below the common hum problem that it can be mostly ignored in the first instance. I have lately finished a little project involving fitting a single termination panel to the back of all my racks, all the signal and power cable screens/grounds are commoned at that panel, where gear has a pin one problem the pigtail from this termination panel has pin one lifted at the receiver, all the pigtails have common mode chokes fitted. The effect has been quite interesting, in that the rig just does not hum, at all, no hums, no buzzes, and I have tested by pushing a lot of current into a screen connections (>10A), the cable got warm, but there was no hum! I no longer have to worry about star grounding (outside of the gear racks anyway), plug in wherever is convenient, screw the multicores in and go. Sorry, but star grounding entire stages is just the wrong way to do it IME. My thanks to T.W. and the theatre sound mailing list crew for turning me on to the right way to do this. AES 48 is well worth the time if you do audio systems, as are the papers by Tony Waldron, Neil Muncy & Bill Whitlock. Regards, Dan. Link to comment Share on other sites More sharing options...
Sound Juice Posted February 16, 2009 Author Share Posted February 16, 2009 The solution is to run the mains for FOH from the stage and then there is just the single earth point on stage. Check, we have a 16A cable attached to our multicore which goes into our PA distro. I have lately finished a little project involving fitting a single termination panel to the back of all my racks, all the signal and power cable... Having got to the warehouse this morning and investigated inside the back of the racks (which have always been fitted with a single termination panel), I'll have a look at the paper you mentioned, then try it out Link to comment Share on other sites More sharing options...
dbuckley Posted February 16, 2009 Share Posted February 16, 2009 The work that has been done on the "pin 1 problem" is facinating, and I've read at least the paper from the Cadac bloke, albeit some time ago. The issue I see is that its all very well having your rig perfect so it can work in any terrible situation but as soon as you subhire or someone turns up with a rack they built there must be a possibility of trouble. The "good 'ole star earth" model has stood the test of time for working adequately well. Link to comment Share on other sites More sharing options...
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