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reasons for an amp to go into "protection"

Discussion in 'Mobile Phones / Entertainment' started by Kevin G., Mar 21, 2005.

  1. Kevin G.

    Kevin G. Well-Known Member

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    Hooked up an old amp that a friend gave me to my Pioneer 12"...
    I took my time and made sure all my wires were clean and no frayed ends. used connectors... Bridged the amp, turned everything down to begin with, and moved from there...
    Powered up, and raised the output and level, It immediately went into protection, (light lit red), and had zero output.
    I double checked my connections...everything seems to be right. I then lowered all the gain and level, and slowly raised each. It got some bass, but cut out fairly early.
    I then un-bridged,(hooked up one side only) and started again. I was able to raise the output more this time, but it still went to protection.
    Anyone know off hand what the prob could be??
    Jim, you out there??
    I know it's not high-end stuff, but I can't think what could be causing this.
    Pioneer HU, 50w x4
    Pioneer SVC 12" 4ohm
    Jensen XH275 300w 4ohm
     
  2. Daniel Johnson

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    There are quite a few things that could be causing this, and without knowing any of the specifics of your hardware, we can try to single a few things out.

    First, what's the impedance on the subwoofer (assuming it's a single voice coil)? What kind of inputs do you have going into the amp (line level or speaker level)? Does the driver work on other amplifiers (perhaps it could have a cracked voice coil)? What kind of enclosure is the driver in?

    Assuming the gear is in good condition, protect mode is generally caused by a few things: shorts in speaker circuits, impedance levels that are too low, or not enough current for the amplifier, though I doubt you're running into current problems. Speaking of which, what wire gauges are you using for the hot and ground leads to the amplfier?
     
  3. Kevin G.

    Kevin G. Well-Known Member

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    Wow, finally, I was beginning to think noone reads the car audio forum....Thanks Daniel,
    It's a 4 ohm Pioneer SVC.
    The amp is a 2ohm stable 150x2, running bridged.
    8ga.(I believe), wire running direct from battery, in-line fused.
    8ga. ground directly to body @ 1.5 foot long.
    Pioneer HU 50x4 pre-outs to amp.
    I have been reading up and down the web, anything I can to figure this thing out, I think I've found the problem, (unless I don't understand like I think I do.) The Speaker Is presenting a 0.8 ohm load to the amp, which is why it is protecting itself...
    I used a DMM pos. to pos. on binding posts @ my box, neg to neg.
    Should I test directly to the speaker itself? Will this be any different.?
    I noticed the guy before me wired the box with like 16 ga.,
    Would that make a difference?
    Caveat Emptor, I guess, Bought it on ebay, had a seven day window to return, Wish I'd have known how to test earlier.

    [​IMG]
     
  4. Daniel Johnson

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    Hmm. The driver should present a load that's in range for that amplifier, as 4 ohms bridged is essentially the same as 2 ohm stereo.

    If you know for a fact that the amplifier works driving other speakers, it's probably the sub, sorry to say.

    One more thing you can try out... Try turning the amp on with nothing connected to the speaker output terminals and see if it still goes into protect.
     
  5. Kevin G.

    Kevin G. Well-Known Member

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    Won't this damage the outputs of the amp??
     
  6. Daniel Johnson

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    Nah, as long as you don't crank the heck out of the gain levels, it'll be alright. You only have to do it for a few seconds to verify whether or not it'll switch into protect mode.

    All you're doing here is checking for an internal short.
     
  7. Kevin G.

    Kevin G. Well-Known Member

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    Well, I hooked up a JL Audio 10/WO tonight, and it bumped pretty good out of one side, as soon as I bridged the amp , though, off to Protect mode again....
    I dunno WTF, but its really pissin' me off!
    My buddy walked across the shop with his 12 W3, that is bridged at the speaker...I added that to the other channel, and could push it as hard as I wanted... As soon as I unhooked the 10 and tried to bridge...Bang!!! Into protect...
     
  8. Adam R

    Adam R Member

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    Even then it wouldn't matter. With nothing connected to the amp's output you could crank the gain to max, drive it well into clipping, and then just let it sit there for hours. With nothing connected there's no current leaving the amp, which means there's no heat buildup regardless of the output voltage or if the amp is clipping.

    If your sub read .8ohm DC then one of 2 things is going on, a speaker wire slipped off of the terminal and is making a short, or the voice coil is blown. Either of which will send the amp into protection immediately. You said it did it with the JL though, what impedance is that sub?
     
  9. eddie-M

    eddie-M Active Member

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    Sounds to me you have a bad amp, if it is still cutting out while just using one side (not bridged) then the amp must be bad, try a different amp.
     
  10. Rudy Cardona

    Rudy Cardona Member

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    let me just get this straight, youre jensen is a 4 channel amp right??? well in that case IT IS NOT STABLE AT 2 OHMS, that is a big no no for class A/B amps and very few can do that, your amp WILL shut off very quickly like that, but youre not presenting anything lower than a 4 ohm load and a jensen amp is of a very poor quality.


    So if youre sub a svc jl w0 4 ohm then when you bridge it , it you should be getting a 4 ohm load, that is perfect and if youre amp still cuts off at that independence than amplifier is bad, since its a 4 channel try to bridge the OTHER 2 channels and see what happens.
     
  11. Kevin G.

    Kevin G. Well-Known Member

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    I have since given up trying to bridge the amp.. since it goes into protect every time I do. (at the amp only)
    I run both channels to Mtx blue thunder 12's It cranks pretty good.
    I know the amp is a cheappie, but it was free...
     

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