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| Thread ID: 58038 | 2005-05-19 12:30:00 | Passive Crossover | george12 (7) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 356728 | 2005-05-23 13:13:00 | Differential loads on a multiphase source can produce inter-phase voltages on neutrals and earths . I have measured voltage levels up to 20v p-p and these can result in micro-shocks on stage for performers handling metal cased mics if they make contact with any equipment connected to an item earthed via another phase line . Significant noise can be injected into the system via this mechanism, and if waylines to a rear-of-house control room reference a different earth (yes, I know they shouldn't but I have found some that do) then electrical noise can reach unacceptable levels . In my system which has been dubbed "Girtee", the mixing desk at the back of the room is ALLWAYS supplied from the same phase of the same splitter box as the power for the backline gear, such as the guitar amplifiers etc . This is one of the reasons we generally use a 3 phase socket and one of my splitters to power the audio rather than any plug we can find around the pub . In the interest of balance, i then use one or both of the other phases to run the amplifiers used for front of house and monitors . This minamises the problem of mild shocks as the stage earthed guitarists gob all over my desk earthed mics . The "earth lift" switch on the D . I . boxes used for keyboards, bass guitar, DJs etc illiminates electrical noise caused by earthloops carrying current over the audio cables between the 2 pieces of equipment earthed at different ends of the building . A feed from some audio device upstairs, or a built in DJ booth is the worst, as i have little control over the equipments power sourse . Just to be extra safe, and reduce the noise in my system and just like everything else i do with a passion, my earthing is always just a little OTT anyway . What makes the three-phase system you linked work is its modular design with the three-phase input direct to the amp, not supplying separate modules . The common low-impedance earth would work much better under that configuration . There might still be problems if a mic audio feed had to head off via a wayline to a control room and back again to a different item of single-phase equipment, but I somehow doubt that this would be a likely configuration for these amps . Yes . . i'm still envyous of the tidyness of a single BIG 3-phase power supply running many amplifier modules, as opposed to 3 phase power being split into several single phase feeds to run several power supplies for individual pairs of amplifiers, as mine does . As for noise problems, these Oceania amplifiers have nothing to do with the wiring between control equipment and mics . Other than the speakers themselves they are at the end of the audio chain, in several racks, usually at one or both sides of the stage . The mics allways are connected not to a control room, but to an audio splitter at the side of the stage that conects them to the monitor desk, and to the FOH desk at the other end of the stadium . The FOH desk then runs these amps (via EQ, delays etc etc etc) All power for the Audio is ALLWAYS run from the same splitter, usually just under the stage somewhere . It takes all sorts of balanced cables and strategicly broken earths to keep the system quiet . I've wheeled enough of the Oceania racks into the Westpac Trust Stadium in CHCH while working as a loader to know and envy them . I still want one one day when i grow up or something . Till then, i'll stick with my labs . :D |
personthingy (1670) | ||
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