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Author Topic: Thump when turning on LED reader Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 05-01-2004 01:59 AM                     I recently installed a Kelmar reverse scan reader. When the LED is turned on, a thump can be heard in the auditorium. How can this be stopped?  |  IP: Logged Mike Olpin Chop Chop! Posts: 1852 From: Dallas, TX Registered: Jan 2002 posted 05-01-2004 02:12 AM                     Put the processor in non-sync or mute before turning on the reader. If your theatre has automation, it can be set up to do this automatically when you start the show. For instance, our system turns on the LED reader as soon as start is pressed, but it does not toggle the processor over to SR until the dowser opens.  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 05-01-2004 12:36 PM                     Yes, that would definately work. But, is there a way to make the LED turn on gradually instead of all at once to avoid a thump?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-01-2004 01:01 PM                     The thump is more likely from the powering up of the preamp than the led I would sujest wireing the led powersupply with the projector motor so it is on just before the changeover switching  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 05-01-2004 08:29 PM                     These days I almost always hook the reverse scam supply across the motor feed terminals as many do not feature an on-off terminal as C.E. does. BACP reccomends theirs always be left on, but on the Kelmar there is no way other than to power it up and down and yes, the thump can actually be from both the plus and minus supplies comming up and the bias that the LED turning on causes on the cell itself. You basically have to do it as Mike suggests......most automation used today switches the processor between non-sync and SR, or digital with sr as the analog fallback. There is no feature for bringing the LED voltage up gradually and being able to do this would not completely eliminate the thump anyway. Mark  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 05-01-2004 08:59 PM                     Thanks for the help.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 05-01-2004 09:02 PM                        So what's the solution for installations which use an exciter-lamp changeover system? Does it have to be reworked with a processor that can do the sound changeover electronically? I am sure that someone here will point out that exciter-lamp changeover systems are cheesy and I agree completely, but I've had to deal with many such setups, as they are fairly common.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-01-2004 09:58 PM                     THe CE is the only one that would allow the led only to be off but you couldn't wire a changeover control to it identically as the old excitor one  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-02-2004 01:20 AM                     CE does offer, upon request, their LS-40 power supply with the logic such that you can replace an exciter lamp changeover system (or an exciter lamp switched system). Just ask for the "Cardinal Mod" You will then need to connect the terminals in the rear to turn the LED on (Factory default is the reverse logic where the LED comes on unless you connect the terminals to turn it off). Steve  |  IP: Logged

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