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Author Topic: intermittent sound dropout Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 01-21-2012 12:33 PM                        I've been trying to solve this problem for over a year. Every time I think it is fixed, it starts again a month or so later. The center channel drops the highs, giving voices the sound of coming through a movie telephone filter. Things we done that have "fixed" it in the past: Replaced LED's in reader Replaced Kelmar power supply for both machines. Replaced the Ashely X1 crossovers on all the amps. Last fall I had two service calls (one to track down the bad crossovers and one to reset the whole A/B chain). In addition we've pulled out and reseated the cards in the Dolby 650 (and cleaned it out). We checked the connections in all of the amps. The LCD display on the 650 shows no dropout of the center channel, but you can hear it on the monitor, which should eliminate a bad speaker (though we checked those, too). Sound was good in November, we closed in December, and the sound was fine for the first week in January. I heard quick bits of it for the first show last week and then was out of town, so couldn't follow up. Last night, new show and it was horrible (thankfully, a subtitled film). The dropout doesn't usually last more than 30 secs. Sometimes it just happens once a film. Last night it was on and off all through the film. Does it in Digital,SR and Mono. What's left? Dolby motherboard?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-22-2012 12:00 AM                        Definatly look at the crossover again. If you still have the older XR-1 crossovers, not the newer ones with no controls, I am certain this is it. You could operate the very small switches on the crossover and then leave them set where they started. Same with the pushbuttons. It is a sad fact that our last project just before closing was to redesign the Ashly crossover due to unreliability in the theatres. Drops right in and is preset for your model JBL speaker. We made 500 of these and then closed. It is possible that an amp channel is bad, but not likely, since they rarely cure themselves. Currently on vacation in Vienna, back Tuesday. Louis  |  IP: Logged Ron Lacheur Jedi Master Film Handler Posts: 650 From: British Columbia, Canada Registered: Feb 2002 posted 01-22-2012 12:33 AM                     Dirty gain pot on the offending channel?  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 01-22-2012 05:51 AM                     Hi there, If I am not mistaken you have not tried replacing the amplifier, yet. If you haven't got a spare one why not swapping, say, the centre one with the left one, to see if the issue follows the amp or the channel? You may also want to find a way to monitor the amp output, does your monitor accept amp return lines? Louis, could it be an overheating issue?  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 01-22-2012 10:01 AM                     It sounds like I've got almost the same intermittant problem, only on my system the LOWS of the center channel drop out, making it sound like a "movie telephone filter". The set up sounds similar to yours. Ashly amps & CP-650. It's very occasional and unpredictable, which makes it tricky to troubleshoot. The input pots & switches on the Ashlys notoriously unreliable. "Exercise" them a bit & see if the problem goes away. I haven't tried swapping my amps yet either, but I probably will next time the sound drops out. Last time it happened was around Thanksgiving week. It dropped out just as I was leaving the booth, but by the time I got back inside, it had 'fixed' itself. It's been behaving well since then but I still don't trust it. Also, on my system, if the problem is going to happen, it almost always only dropped out during the trailers or the first reel of the feature. I never had it go out during the middle of the film. That first lead me to beleive it's perhaps a temperature related issue, but sometimes I come in early to do work and the amps are on for several hours before the first show, which you'd think would give them time to 'warm up' & stablize by showtime. So no matter what, it seems to be happening randomly. Very vexing! Sometimes I wish it would just catostrophically fail. It would be much easier to troubleshoot!  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 01-22-2012 10:17 AM                        You say that this is audible on the booth monitor. Is that with the monitor set to the "amp" position or the "processor" position? Or both? You are not using the Dolby crossover card, correct? Does the problem occur with the processor in bypass mode?  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 01-22-2012 10:59 AM                        Louis: What's the best way to contact you when you get back?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-22-2012 11:09 AM                        Cell phone works; fax does still for a little while.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-22-2012 11:10 AM                        Cell phone works; fax does still for a little while.Louis  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 01-22-2012 11:49 AM                     I'm with Ron on this one. Seen it happen a lot once Ashley amplifiers get some age to them. I would recommend you turn off all amplifiers except center and with something fairly constant audio playing (maybe a loop of a trailer) jiggle the gain pots on the back of the amplifier and see if you can make it drop. If so, that's your problem.  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 01-22-2012 03:48 PM                        Spent about a half an hour playing with the levels. Couldn't force it to go out, so maybe dirty pot is the immediate problem. And, as with Jim, it was the low freq going out, not the high (so much for my musical skills). Lowering the low freq perfectly replicated the problem. I'll just have to keep an ear out for it happening again.  |  IP: Logged Dominic Espinosa Phenomenal Film Handler Posts: 1172 From: California, U.S.A. Registered: Jan 2004 posted 01-22-2012 03:58 PM                     Ironically I too had a center channel dropping out highs rather than lows intermittently a while back. Thought it was the xover but it turned out to be the horn driver. Nevertheless I'm curious as mentioned above: when it's dropped out do you hear full signal from the monitor listening to the amps or processor or both?  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 01-22-2012 10:35 PM                     Sounds like assumptions are being made before this important question is first answered. quote: Scott Norwood You say that this is audible on the booth monitor. Is that with the monitor set to the "amp" position or the "processor" position? Or both?  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 01-22-2012 11:40 PM                     ..swap the diaphrams the HF horn drivers between L and C...windings on those diaphrams can open up when they want to.  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 01-23-2012 11:43 AM                     You're assuming that the monitor has a "processor" function, and that it's actually wired up. But with amplifier crossovers (my least favorite kind) the processor monitor won't tell you much in this case. I haven't come across a processor without crossovers that managed to filter all the highs or lows out of a full range signal, although it is possible. This is most likely the Ashley crossover module has failed, they do. The volume control pot is also known for failure and noise (cheap unsealed potentiometers that are never moved all eventually become unreliable, and high quality sealed pots are expensive).  |  IP: Logged

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