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Issues with Driverack PA - Volume deteriates slowly

bobforsbobfors Posts: 11
edited June 2007 in PA General Discussion
Am running JBL JRX 115's through a QSC 2450 and JBL 118S's through a QSC 850 via an Allen and Heath MixWizard WZ3 16:2. Everything has been working GREAT until the other day...we noticed the output volume was slowly detiriating over the course of a set. Had to stop and reset (turn off and on) the PA. Then the volume was fine again for another almost full set (30 minutes).

I have troubleshooted the heck out of everything (mixer, subs, mains, etc)even with another small Yamaha PA...no issues

Any ideas why this would happen? It's definitely the PA doing it. Fix? Please help.

Bob

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    kpippenkpippen Posts: 551
    Hi Bob,

    Just curious: Did you notice if the DriveRack was getting warm?... Have you tried a hard reset as described in the manual (not by just cycling the power)?... Did you setup the gain structure?... Was the DriveRack clipping?... Were your amps clipping?... What do your speakers sound like when it starts to deteriate?... Are you using compression?...
    bobfors wrote:
    Everything has been working GREAT until the other day
    How long has has everything been working great?... What has changed?... What have you just tried or changed recently?...compression?...

    Also,...are you running the subs in stereo/parallel mode or bridge-mono mode on the RMX850?... IMHO if in stereo/parallel mode you may be way underpowered but it's probably not related to the problem in hand...

    Kevin
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    bobforsbobfors Posts: 11
    Have not tried a hard reset.

    Has been working well for close to 1 year. Nothing was clipping, and am not using compression.
    Speakers dont sound like anything as the volume decreases. Gigs start out very normal and sounding good, and the volume just deteriates...no unusual sounds or anything.
    It's like someone is slowly turning down the volume over a 20-30 minute period of time.

    Running subs in the bridged mono mode.

    Gain structure? Didnt see that in the manual anywhere.

    Thanks for the reply!!!!

    Bob
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    kpippenkpippen Posts: 551
    Hi Bob,

    I would do the hard reset as described in the manual... Be advised that you will need to re-enter your program afterwards... I would also set the gain structure as described in \"Appendix A\" in the back of the DRPA manual but it's probably not related...

    Do you know if you were getting adequate power (120VAC) to the DriveRack when this happened?... Did it happen to the 115s to the subs or both?... Are you using battery type UPS in front of the DriveRack?... If so...is it a cheap one or a decent one?...

    Kevin
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    bobforsbobfors Posts: 11
    WIll try the hard reset and look at the gain structure you mention.

    Never had these issues before though and have not changed anything over time. Very strange that the colume slowly deteriates over time......
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    kpippenkpippen Posts: 551
    Hi Bob,

    These might be some key questions to consider... If you were out giging and nothing was changed with your equipment then was your power source the only thing that did change?...

    Do you know if you were getting adequate power (120VAC) to the DriveRack when this happened?... Are you using battery type UPS in front of the DriveRack?... If so...is it a cheap one or a decent one?...

    Kevin
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    bobforsbobfors Posts: 11
    Definitely know I was getting adequate power. It happened at practice last week inside at 72 degrees, then outside at a gig this past Saturday.

    I do have a Power Conditioner in the chain, but do not have a UPS at all. Is this recommended?

    The strange thing is that everything else was fine and didnt notice any spikes, or other equipment doing anything strange...just a steady decrease in volume on the main's....


    Bob
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    kpippenkpippen Posts: 551
    bobfors wrote:
    I do have a Power Conditioner in the chain, but do not have a UPS at all. Is this recommended?
    Hi Bob,

    A UPS is recommended prior to the DRPA so it won't shut down before your amps in the event of a power interruption... Based on information posted here and on other sites the DRPA has the potential to spike amps if it's turned off before the amps... Since a lot of folks are using a battery type UPS to prevent this... I thought a cheap one could be causing a problem... Hey,...it's just a process of elimination...
    bobfors wrote:
    The strange thing is that everything else was fine and didnt notice any spikes, or other equipment doing anything strange...just a steady decrease in volume on the main's....
    Are you saying that the subs are NOT decreasing in volume when this occurs?... If that's the case I would switch the amps to see if the problem follows the amp or not...2cents.gif

    Kevin
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    bobforsbobfors Posts: 11
    Will look into a UPS....great idea anyway....

    I thought I troubleshooted the amps out of it, but I used a smaller PA and bypassed the amps. I didnt repower the amps though when it happened...just turned them down for a second, re-powered the Driverack (turned it off and back on) and then turned the amps back up...fixed it....normal volume. If it were amps, thinking I would have had to turn them off and reset, etc..... crazy.....

    Will check the subs also. Could not tell if they were decreasing also...just didnt have any siound. Assuming so.

    Bob
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    kpippenkpippen Posts: 551
    Bob,

    I would try leaving the DriveRack on and only cycling power to the amps... The result of that step may either isolate or help us in figuring out what's going on...

    Has any wiring or cabling been changed prior to the problem?...

    Kevin
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    bobforsbobfors Posts: 11
    No....no cabling changes. As I said up front...everything was running fine, then all of a sudden last week at preactice, we all noticed a decrease in volume in the mains, and I just turned off the driverack and turned it back on...all was solved, until Saturday when it happened again. It starts out normal, and decreases over 30 minutes.

    Will try the amp reset to see if that isolates it any further.
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    kpippenkpippen Posts: 551
    bobfors wrote:
    Will try the amp reset to see if that isolates it any further.
    Another thought: you might also try muting the channels on the DRPA for a couple of seconds to see what happens...

    Kevin
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    DraDra Posts: 3,777
    Something else to try to eliminate the amps. Set up without using subs and play until the \"thing\" happens. Then without turning anything off, unplug the high outputs from the DRPA, and then unplug the input cables to the DRPA and direct connect them. What happens? If the problem goes away then re-patch the DRPA without powering anything down. Problem back? If not, go ahead and re-bypass the DRPA as before and play until the problem returns (or at least 2x as long as usual. If it doesn't happen then, I think that you can rule in the DRPA as the culprit.
    Just remember, when troubleshooting, only change one thing at a time.

    Dra

    PS- the DRPA doesn't have mutes to punch in and out. But you can turn the x-over gains down to inf (off)
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    kpippenkpippen Posts: 551
    edited June 2007
    I was wondering if you were going to chime in?...

    Bob,...It's best to follow Dra's procedure... What he's suggesting makes a lot of sense... He knows a lot more about this stuff than I...:)

    Kevin
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    bobforsbobfors Posts: 11
    Thanks so much to everyone for all the replies. Will try those latest posts and see.
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    MikeyMikey Posts: 82
    How old are your amps? This sounds like one of two things-power compression (not likely) or bad capacitors in the power amp's power supply (much more likely).

    It could also be a thermal problem, but the reset that you did would not likely have allowed enough time for anything to cool.

    Have you tried just plugging a signal directly into the power amp and the amp to the speakers? How did you isolate the problem to the DRPA?

    As others have said, the hard reset is always a good place to start.

    Please post back.

    Mikey
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    DraDra Posts: 3,777
    Kevin, your too kind. I got pretty good at trouble shooting because 10-15 yrs ago I had a lot of crap gear. Well not crap gear, just bought 2nd, 3rd, 4th handed stuff. Crest, QSC, Peavey amps, home made FOH cabs and monitors, digi-tech 15 band EQ, Peavey board (the one with the spring reverb that if you bump it during convention speach would go \"BOOOOONG\". Yamaha boarbs and EQ's. Trouble shooting was a given for every set-up. Why no sound? Where's that buzz coming from? Etc What dimmer channel are the lavenders on? Why did the ambers come on with the Blues.
    A bit of trivia... Edgar Winter refuses to have any green stage lighting. Ever seen an albino under a green light.

    Dra
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    bobforsbobfors Posts: 11
    Update....

    I hard reset the Driverack and did some other troubleshooting. Found a bad XLR cable that was going from the left channel - high to the left channel on my amp. Thinking an overload on one channel may be the culprit, or have something to do with it.

    Still strange even with a bad cable that after powering off and then on again, it fixed it. I thought once cables went bad, they went.

    One thing I noticed is that I dont have a lot of picks for Amps and Speakers in the wizard. I may have one of the first models that didnt list the equipment I have now. The recent owner's manual has an appendix that lists available choices, and they are listed there, but are not on the Driverack itself.

    Band practice tonight...will see if that took care of it.
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    DraDra Posts: 3,777
    This from the 260 GUI

    tops amp - 37%
    Subs amp - 41%

    Tops Hi-pass 125hz BW24 (0 db)
    lows Hi-pass 45hz BW12 Lo-pass 125hz (-.2db)

    Lo PEQ 45hz Q 1.215 (+6.5db)
    162hz Q.939 (-3db)

    Limiters - both +18db over easy 4 (260 has a brick wall, the PA does not so bare that in mind)

    You are luckier than most, getting the PEQ settings.

    Dra
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    bobforsbobfors Posts: 11
    What would you pick for the amp and speaker type.....Cutsom? You list 37% and 41%....I dont remember seeing a choice on \"Custom\".....

    I have JBL JRX 115's through a QSC 1450 for mains and JBL 118S's through a QSC 850 for subs.

    Assuming the first list of specs are for the compresor settings?
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    DraDra Posts: 3,777
    The first specs are the amp attenuator knob positions. 37% of full on, 41% of full on.
    Yes, select custom for amps and speakers.

    The other settings are for the crossover, PEQ speaker tunings.

    What are you referring to with compressor settings?
    Don't use the compressor useless you what everything to be compressed if your signal peeks. Limiteras are what you will need to use protect your speakers.

    Dra
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    wolfgongwolfgong Posts: 74
    Gents -

    Cables.
    I can say without reservation that bad cables can be intermittent. In other words they can work fine and then if you twist them just right, and viola, you have your problem right back.

    I've gotten to the point with cables that if they fail once, I toss them. I know people who spend hours trying to fix cables where they think the problem is only to find they haven't fixed the problem after hours of work. Cables are the backbone of any system if you have one intermittent cable in your configuration, it can ruin many venues.

    Volume decrease.
    The problem of the volume change sounds like an amp is going into thermal protection for some reason. It sounds like it happens gradually.

    One thing that may cause a similar gradual thermal condition is a build up of low frequency which over time is over loading the amp.

    Have you set the 'selectable low frequency filters' on your amps. You can set them for 30Hz or 50Hz according to you amps spec sheet. This may help.

    W
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    bobforsbobfors Posts: 11
    Hard reset everything, set the settings per a couple of these replies, and replaced a bad output XLR cable to the amp. All is good. it appears the thermal protection thing was the culprit with the bad XLR cable. Driverack PA is sounding better than ever.

    Thanks to EVERYONE for the replies!!!!!

    Rock on!!!

    Bob
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    kpippenkpippen Posts: 551
    kpippen wrote:
    Has any wiring or cabling been changed prior to the problem?...
    I've always been a firm believer in that "Your cables are your sound!"...:)
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