#881436 - 12/11/99 09:48 PM
A.C. NITEMARE
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PJR
Gold Member
Registered: 08/09/99
Posts: 653
Loc: Orange Co, Ny
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My band just finished a corporate Xmas gig at a fairly large catering hall fri nite.We set up in the afternoon because it was a place we had not played at before and wanted everything to be just right.There was to be approx. 300 guests . When we arrived we found to my delight a very spacious stage with 3 separate 20 amp lines which were tracable to the power box behind the stage.At this point all systems looked to be great, enough 'juice' to power the amp rack, stage amps and lighting without fear of blowing a fuse. We set everything up and did a quick sound check and everything was great. The PA was whisper quiet with 0 input as it should be , and all my testing gear indicated ample current . So, we all went home to relax and get cleaned up for the nite to come.We returned about 45 min prior to showtime , and when I turned on the PA a very loud obnoxious high pitched buzz, much like a giant mosquito, was eminating from the mains.I mean this was loud .It was now scramble time for me as I unsuccessfully attempted different electrical configurations to rid my PA of this horrible sound, which was not present just 4 hours earlier.I tried everything, different AC box, different amp configurations, I could not even dial out the noise from the EQ. The show had to go on, and I'd venture to say that most of the guests did not notice the hum, as the music did drown most of it out.I knew it was there .About 40 minutes into our 1st set, it grew even louder, then disappeared almost to nothing.The remaining 2 sets went wonderfully with no AC noise or buzz whatsoever.The next day I set up the same equip in my rehearsal room with no problems. I cannot come up with a valid reason why this occurred. Is it possible that somewhere 'upstream' from the stage power was the culprit, maybe the kitchen, (it was around dinner serving time), or microwave activity?? Is there anything I can do to prevent this ??? just wondering. signing off, Peter, ac is not my friend.
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#881437 - 12/12/99 08:01 PM
Re: A.C. NITEMARE
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gigeditor
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Registered: 08/20/99
Posts: 27
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Peter
I have had similar problems and they are almost always due to something else (usually kitchen or AC) using the same circuit. I once had a "thump-thump-thump" kind of sound coming, not through the entire PA but just the channel that powered my MIDI guitar rig. Turned out my rig was plugged into the same circuit that ran the ceiling fans and I only figured it out when i noticed that the thumps were in prefect time with the rotation of the fan. Unfortunately, short of completely isolating the AC for your system, it's probably back to the old process of elimination.
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#881438 - 12/14/99 05:10 PM
Re: A.C. NITEMARE
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eddieray
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Registered: 11/04/99
Posts: 25
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We've played places where the hum thru the guitar amps was really bad. Isn't there some kind of hardware device available that could help reduce it or eliminate it?
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#881439 - 12/14/99 07:44 PM
Re: A.C. NITEMARE
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Mark Amundson
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Registered: 10/30/01
Posts: 5
Loc: Cambridge,MN,UNITED STATES
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Your AC nightmare has no really cost effective cure. Possible cures would be: 1) Power conditioning suitable for the gig and the noise source, and/or 2)a separate power source (typically a generator cart).
I can't be certain, but I suspect kitchen microwave ovens or other motor driven appliances are the culprits to your bad (noisy) AC. This kind of noise is too low in frequency to be filtered by typical EMI/RFI elements in most rack power conditioners and is to high in frequency to be handled by automatic voltage regulators.
There are "no excuses" power conditioners out there that deliver perfect AC, but they intended for small loads and not the heavy jobs like gig power. And way too expensive besides. Genny carts are good solutions, but they rent fairly expensive and you really have to have the "big time" power distro system to plug-in. Besides, most hotels probably do not appreciate power feeders in their hallways and the humming genny cart near the guest rooms.
Mark Amundson,
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