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Thread: Please Help, Factory Amp Cutting Off

  1. #1
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    Please Help, Factory Amp Cutting Off

    I recently installed an amplifier and subwoofer in the car. I followed the wiring instructions in the BAV Audio manual for splicing into the L, R, and Remote On. Everything works beautifully when the car is off, radio on. When I drive the car and turn it up really loud, the factory amp will stop working and all audio shuts off until I turn off the car, and restart or turn on the radio again. Turning off the radio and back on without shutting down the car doesn't help. The head unit still functions, just no sound.

    When the symptom occurs, the amp and crossover still have power and pass audio so it's definately something wrong with the stock amp. I only have 175W RMS so it's not like I'm drawing 75 amps from the battery. Is this common? Do I need a capacitor?
    Last edited by Carhopper; 05-14-2011 at 12:17 PM.
    2002 E46 M3 Conv SMG - M for life!

  2. #2
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    I read a little bit that others have had trouble with the remote power on, white wire from the head unit. I measured the voltage and it is 10.9v with or without my amplifier attached. Then I decided to put in a relay as others have suggested to try and drop the load on the wire. I tested the current to my amp and it is 18ma. I connected a 12v relay I picked up from Advance Auto and it is drawing 246ma so I don't think it will put it in.

    So where does that leave me? Again, it only happens when the amp hits really hard and the car is running. Could this be a capacitor issue?
    2002 E46 M3 Conv SMG - M for life!

  3. #3
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    It hasn't happened again, I just avoid turning up the factory amp all the way. Who knows, the problem might have been there and I just never turned it up so far. It's easy to turn it up more than before because the massive bass drowns out the distortion that I might have heard from the smaller speakers.
    2002 E46 M3 Conv SMG - M for life!

  4. #4
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    I'm not a super expert, but when you are turning up the volume, you must remember your are pushing the relatively little RMS output of the amplifier into distortion and thus extra heat, it's probably going into thermal shut/cut out protection mode..

    So the resolution for you is another layer of compromise, in that you can't turn the volume up!

    As mentioned before, the route of splicing into the outputs of the oem amp is a basic and relatively rudimentary way of doing things, and you're discovering all the compromises. I hazard a guess at some point you'll get miffed with this setup and look into a more purposeful and reliable and much better quality sounding setup!

    Cheers, Dennis!

  5. #5
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    The system cut out on me 3 times yesterday and it's definately related to high volume, although I got it to cut out with my factory amp gain turned all the way down so it's not related to undercurrent from the amp. I disconnected the RCA inputs going to my crossover (before the amp) and it didn't cut out all the way home with factory amp only, this tells me that the input impedance of the crossover is probably a little low and is drawing down the signal enough to cut out the factory amp and/or head unit. Ultimately you want audio input devices to have infinite impedance (impractically speaking), and outputs to have zero for maximum power transfer. This morning I put a 10K resister in series with the signal wire into the crossover, thus dropping my signal about 10db (trained ear measurement). I still have plenty of gain in the crossover and amp to make up for the difference. I'm thinking this isolation will fix the problem. Off to test it today.
    Last edited by Carhopper; 05-21-2011 at 08:49 AM.
    2002 E46 M3 Conv SMG - M for life!

  6. #6
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    Still happened at 10k, but seemed to last longer, although one of them was only 5k, read the color bands wrong. None the less, went to 100k. This dropped the signal significantly, but still plenty of gain to drive the amp with some headroom.
    2002 E46 M3 Conv SMG - M for life!

  7. #7
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    Before I even tried the 100k I had a revelation that was so obvious and the problem is fixed. The factory signals from the head unit don't use a common ground system. When I measured the impedance from ground to ground, I got 10k. When I measured the inputs on my preamp, they were 170 ohms to ground and 0 ohms beteen them. The solution is to put 10K resistors on the signal and ground for left and right, total 4 resistors. Bass is cleaner and no problems. I'll report back if it fails again,but I just went on a long run with it blaring and no problems...except maybe from my neighbors, one of which is a city police officer.
    2002 E46 M3 Conv SMG - M for life!

  8. #8
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    Seems like such a LOT of bother to go through!

    tongue in cheek - if you do get it all working how you want, the oem amplifier will probably crap out and die on you !

    And you're doing all this becuase? you want to keep the oem audio components.. right?

    Cheers, Dennis!

  9. #9
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    Yeah, the idea was an inexpensive subwoofer upgrade. I used the instructions from Bav Audio on the wiring, but their amp must have had some isolation from ground. That's what I get for trying to do it myself, but it was a learning experience. This is how we innovate and help others.
    2002 E46 M3 Conv SMG - M for life!

  10. #10
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    One alternative now that I know that the factory signals are differential, would be to use an amplifier with differential inputs. I still like having the 10K isolation though because I'm splitting the signal passively so it puts less load on the head unit. A balanced to unbalanced transformer would work too, I just cheaped out.
    2002 E46 M3 Conv SMG - M for life!

  11. #11
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    Here is what I ended up with as the best config. The inverting (-) output shouldn't be grounded or connected through a resistor because it creates a voltage divider that's useless. The outer shell of the RCA is grounded on my crossover, so an inverted inputs does absolutely nothing. I also removed the resistor from the tip because it really doesn't server a purpose either. I thought it was isolating the signal, but can actually create a low pass filter due to reactive inputs and outputs from the amp and crossover. This config works well in the picture.

    Lesson learned: Buy an amp with differential isolated inputs, many manufacturers make them now.
    Attached Files Attached Files
    2002 E46 M3 Conv SMG - M for life!

  12. #12
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    Hi

    At least you admit and know more now! I'm not saying I know it all - there's some very experienced and much more knowledgeable guys than me ! - however, I think in the post you made about a budget subwoofer and that you'd chosen the wrong sub to be powered by the oem amp, I think I mentioned then to get a processor which cleans and sums the outputs so you can choose any suitable aftermarket amplifier, and I 'think' I mentioned that some amps already come with those so may well go for those instead.

    As I mention in my posts, I am in the car audio trade and I'm looking to 'simplify' things for the majority of enthusiasts and non enthusiasts out there alike, so keeps the frustration as low as possible! I'm 'frustrated' just reading the run around you've posted about and things you've done! but hey, you're learning !

    Cheers, Dennis!

  13. #13
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    It never pays to be cheap and try to piece meal a project.
    Last edited by Carhopper; 05-25-2011 at 07:16 PM.
    2002 E46 M3 Conv SMG - M for life!

  14. #14
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    Hey Carhopper,

    I suffered from this, In Florida the heat is unbearable. With my lack of Funds and knowledge, I scurried the forums and was able to figure out, as well as you that my factory amp was to blame for my cutting in an out. I'm not sure how hot it is by you, but last summer, i had to just simply buy a replacement factory amp, it ran me 76$ and it was plug and play. Turn the clock ahead 1 year later, a week ago, the amp cut out again, just like it did last summer, along with for me, my Final stage resistor (yes i just went all of august in Florida with no A/c). Same situation strapped for cash, I tired like i did with that last amp to find if i could see any visual problems on the board, found nothing, and followed advice to try to de-corrode the terminals with a solution like vinegar, which i did. Now i have a melted amp, melted connected so i cant even buy a new amp, and no music, still no ac, and no money. How do people do life.

    Anyways, basically the reason I'm posting is that with experience in these amps blowing out, THEY HATE HEAT, so anything you can do to prevent yours from getting hot.

    I hope you find better luck in your travels!
    Last edited by Mwantuck; 09-20-2018 at 11:01 AM.

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