Car audio - what would cause an amp to cut out?

Discussion in 'The Garage' started by jlee, Apr 5, 2011.

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  1. jlee

    jlee Lifer

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    '91 MR2
    Infinity Kappa Five
    Infinity Kappa Perfect components
    Dayton 10" subwoofer

    The amp and crossovers are mounted to a board in the frunk. The amp is wired directly to the battery with 8ga cable (about 3ft of cable, basically enough that you can pull the rack out to mess with it without disconnecting everything).

    The crossovers are wired to the tweeters and woofers with 16ga speaker wire (equal lengths for all of them). The amp is set to 2ch / bridged. The subwoofer is wired with 10ga speaker wire to the subwoofer channel on the amplifier.

    The problem is whenever I turn it up to moderately high volume (not ear-splitting, but say t-tops off at highway speed volume), the woofers and subwoofer cut out. The tweeters play quietly for a few seconds, then everything kicks back on. If I run a lower volume, it's fine indefinitely.

    I can run 4ga power and ground cables, but I don't see how that'd be the problem given that I have such a short run (and I'm not listening at max volume). Any ideas? I had the same problem before I tore into the car (just was running a 5.25" subwoofer instead of a 10"), so I know it's not anything I screwed up in the last few days. :p
     
  2. alevasseur14

    alevasseur14 Golden Member

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    Is it possible the amp is overheating? I'm no expert but that's what it sounds like to me.
     
  3. jlee

    jlee Lifer

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    It doesn't have to be on for long - matter of seconds. If it's overheating that fast, there's something wrong (well, there is something wrong, I guess..just hope it's not the amp :p).
     
  4. alevasseur14

    alevasseur14 Golden Member

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    Wow, no kidding. How old is the amp and how many volts are your deck's pre-outs?
     
  5. jlee

    jlee Lifer

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    The amp is brand new (well, last year, but probably less than 5 hours of use on it). 2.2v pre-outs to 2M-long KnuKonceptz RCAs.
     
  6. alevasseur14

    alevasseur14 Golden Member

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    Wow. That's really weird. I'm sure you've double checked all the power connections but that's really the last thing I can come up with. Hope you get it worked out!
     
  7. fbrdphreak

    fbrdphreak Lifer

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    Sounds to me like the amp is having some kind of trouble sending power to the woofers & subs (being that they are the units that draw the most power and your tweeters continue playing).

    An interesting test would be to measure the output at the amp (via multimeter) when playing normally and then under the conditions that cause it to drop.

    If the power output at the amp is the same during both conditions, it's safe to say the problem is between the amp & speakers. If the amp output drops, then there's your answer.

    Couldn't hurt to re-check all of your connections and re-do any that are at all suspect.
     
  8. jlee

    jlee Lifer

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    Wouldn't that mean the wiring to both crossovers and/or both woofers and the subwoofer would all have to be messed up? I just wired the subwoofer today and it's doing the same thing that the last one did, and I ran new wire.. :/

    I do have spade connectors connecting all the speaker wires close to the amp so I can pull the whole rack for autocross/etc..would that cause an issue somehow?
     
    #8 jlee, Apr 6, 2011
    Last edited: Apr 6, 2011
  9. fbrdphreak

    fbrdphreak Lifer

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    Spade connectors should be fine, to my knowledge. Good point on the wiring, but again something to check.

    Definitely put a multimeter to it.
     
  10. Howard

    Howard Lifer

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    The sub is running off the dedicated input on the amp from the HU, right? But the woofer and the subwoofer die simultaneously? That rules out the crossover, so I would guess that the amp cuts out if its supply voltage drops below a certain point... possibly because there is a poor ground somewhere.

    EDIT: You can borrow an oscilloscope and watch the voltage on the amp power terminals?
     
    #10 Howard, Apr 6, 2011
    Last edited: Apr 6, 2011
  11. jlee

    jlee Lifer

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    The battery is old and the negative terminal is not the greatest around...I may try replacing the battery and/or the terminal tomorrow and see if that helps. Thanks!
     
  12. Howard

    Howard Lifer

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    Well, the crossover isn't something that concerns me at all, anyway. If it works at low power, it'll work at high power, provided it's built decently.

    It's probably the amp... if you have a 'scope, and check the outputs of the HU during the silences, you can figure out where in the signal stream the process is pooched.

    EDIT: If the negative terminal is bad, the lights would dim under high load in some situations, too... have you double-checked all the wiring?
     
    #12 Howard, Apr 6, 2011
    Last edited: Apr 6, 2011
  13. EightySix Four

    EightySix Four Diamond Member

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    To me it sounds 100% like a power issue. The amp is clipping due to a lack of power for one reason or another and going into protect mode.
     
  14. Smoove910

    Smoove910 Golden Member

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    Why would you worry about the negative terminal being bad? It is something that needs fixed, but your amp shouldn't be connected to the negative terminal anyways. Personally I would re-run a short 8 or 4 guage ground wire from your amp and find another ground. In my car I used a bolt that secures the spare tire. Of course you will want to sand the paint off in the area you are connecting the ground to so you are contacting bare metal.

    Another option is to ensure your remote wire doesn't have a short. This is the wire from your deck that tells your amp to turn on/off.
     
  15. Possessed Freak

    Possessed Freak Diamond Member

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    Try the simple things, toss a multimeter on the battery posts and have somebody turn up the volume. If the voltage dips, then you know the problem.

    It doesn't sound like a shorting issue as it works at lower volume, but you can always make the system an external one (pull it out of the car and run everything outside) and make sure your wiring is good.
     
  16. jlee

    jlee Lifer

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    Grounding it elsewhere doesn't matter - same problem. I can check the remote wire...there might be a sketchy connection in there from a previous owner.
     
  17. Smoove910

    Smoove910 Golden Member

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    Since your negative battery terminal is corroded, is the positive one corroded too? Me wonders if your power connection needs reran due to corroding connections.
     
  18. jlee

    jlee Lifer

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    It's not corroded, but either the post is no longer as big as it should be, or the negative terminal has worn out and won't grip very well. Everything is clean, but I need to push down on the negative terminal while tightening it for it to get a good grip. I don't see why it wouldn't work now..it'll start the car, but it could be tighter.

    It's definitely not all nasty and dirty (taken pre-wiring):

    [​IMG]
     
  19. FuzzyDunlop

    FuzzyDunlop Diamond Member

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    This

    To me it sounds like your amp is not getting the juice it needs to run the woofer at that level. The amp is grasping for more power, and cant draw any more from just the battery, and is cutting out. Try installing a capacitor between your battery and the amp on the positive side.
    This will also help prevent light dimming during hits.
     
    #19 FuzzyDunlop, Apr 6, 2011
    Last edited: Apr 6, 2011
  20. Howard

    Howard Lifer

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    Band-aid approach, especially since the issue occurs at volumes that are not unreasonably high.
     
  21. jlee

    jlee Lifer

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    I think I'll start by rewiring with quality 4ga wire with crimped and soldered connectors and see what happens. I'm using remnants of a WalMart wiring kit with ring terminals from god-knows-where, and they might have a crappy crimp job too.
     
  22. DominionSeraph

    DominionSeraph Diamond Member

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    As the Kappa Five's thermal protection apparently doesn't shut down the amp (so that's not it), I'd say it's likely one of your speakers (probably the sub) has a partial short.
     
  23. jlee

    jlee Lifer

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    I had the same issue with the previous sub (which was a factory replacement). By partial short you mean a faulty speaker, or bad wiring at a speaker? I could pull the door panels and check..
     
  24. DominionSeraph

    DominionSeraph Diamond Member

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    It would have been in the voice coil of the speaker. But if you had the same issue with another sub then that's not it. (You can look up the DC resistance of the sub and do a resistance check anyway, just to be positive. Disconnect the speaker leads from the amp and just read across those)

    Try running it with just the sub connected.
     
  25. Smoove910

    Smoove910 Golden Member

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    Is that black wire on your battery the ground to your amp? That could be a problem if it is... What are those blue wires? They look like RCA cables or speaker wire
     
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