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Thread: Using the amp from a headunit seperately?

  1. #1
    Maximum Bitrate MikeHunt79's Avatar
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    Lightbulb Using the amp from a headunit seperately?

    OK, so my stock HU is broke, so i'm thinking of ripping the guts out and shoving a epia board in there along with all of the associated gubbins. The only problem now is powering my speakers.

    I don`t really want to get an external amp since i have very little money, they are bulky, and I would like to make a unit that replaces a normal head unit in every way - eg providing amplified speaker outputs. This would also make it easy to use the unit in different cars.

    Heres my idea:

    What if I could get the amp out of my HU and run it seperately? How hard would this be? Has anyone attempted this sort of thing before? What would be needed? Any info, advice or relevent linkage appreciated.

    EDIT: When i say run it seperately, i mean keep it in the HU's box, but ditch everything else (tape deck, tuner, etc.)

  2. #2
    Variable Bitrate mp3hombre's Avatar
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    It can be done but it would require some knowledge in electronics and good detective work.
    Having the schematics would make things easer, too. But if you can't get them, this is how I would do it:

    Open the unit.
    Follow the speakers outputs from the connector or wires to a big chip (the audio amp) inside the HU.
    Write down everything that's written on that chip and google it to find any info on it, like a schematic from an application note or something. That will help you locate the chip inputs and a good place to tap a 1K-2K 1/4w resistor per input.
    Don't touch or remove anything else from the board.
    Look at the image below to have a better idea.
    The Buffer Amp is the audio amp chip, pins 2 and 6 are the audio inputs.
    This might not work if you remove the HU's front control board, that's because the microcontroller in it turns the audio amp chip on/off. It all depends on the HU you have.

    Good luck!!






  3. #3
    Maximum Bitrate MikeHunt79's Avatar
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    Thanx so much mp3hombre. This is exactly the sort of info I was after. I think I should be able to do it, as i've go a couple of weeks holiday coming up. Looks like my limited knowledge of op-amps might come in useful after all. I`ll post any progess I make.

  4. #4
    Variable Bitrate mp3hombre's Avatar
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    Glad I could help!
    One more thing. In the setup above, you're gonna have to control the volume using software (winamp,etc.).
    If your HU came with a "manual' volume control, that would be an ideal place to tap the resisitors in.

    And yeah keep us posted!

  5. #5
    Variable Bitrate
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    Just wondering why you've hacked up what looks like the cdrb20 schematic to do that?
    It has audio inputs on it, thats the point right?
    Im confused

  6. #6
    Variable Bitrate mp3hombre's Avatar
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    Yes that's a cdrb20. I used its schematic as an example because I didn't have any other one on hand.

    I modded an old Pioneer HU some years ago, I did it the way I described above, and it worked.

    Sorry about the confusion.

  7. #7
    Maximum Bitrate
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    I suppose that it depends what it is that is broken about your stock HU... It could be the amp itself

    Really, it's going to take you a lot of time to track that down, and if your HU doesn't power up at all then it doesn't matter if you hack an AUX-IN (which is essentially what you're trying to do), then you have to worry about powering the amp, adding in a switch, etc, etc. Why not just get a real amp? You can get them cheap, and they're no less portable then a broken HU + computer, if anything more portable because then you don't have to remove the car's HU to bring it to another car.

    And if your HU is broken to the point at which it's impossible to add an AUX-IN, then you've just wasted a whole lotta your time trying to do this.

    If you really want to try, you could always build a mini amplifier yourself, possibly using parts from your radio, to save cost.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  8. #8
    Variable Bitrate mp3hombre's Avatar
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    Let's look at the good side.It's going to be quite a learning experience!

  9. #9
    Maximum Bitrate MikeHunt79's Avatar
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    I like to learn. I probably won't start it till the summer tho, since thats when I should be starting my single DIN unit... I got hold of a cheap 4 channel amp to power my speakers in the meantime.

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