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    tesladude's Avatar
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    Technical problem with rear speaker amplifier!

    I am adding 2 extra rear speakers in my jeep, I have some rca cables comming from the rear speaker pre-amp outputs from the back of my pioneer stereo.
    My plan which works beutifully is a dc-dc boost module bringing the cars 12v up to 20 for the main amplifier.

    The main amp is a 2x25 watt class d module I got from online which actually works suprisingly well,
    but this is what is going on...

    I have the modules laid out in the back of my car with the 12v line and ground line I am going to use.
    You need to keep in mind that both the module and the stereo are using single supplies, and so the rca ground is just connected to the entire cars ground, and sence the module is a single supply it too has the imput ground just connected to the entire cars ground through the modules negative powersupply pin.

    So when everything is connected and all grounds are grounded, I turned on the module and I herd a big pop out of I think all the speakers in the car (but I couldnt tell) and there was no audio,
    only when I took power off of the module did I hear audio even through the rear speaker I had hooked up, but it only lasted as long as the decoupling capacitors were charged.

    I messed around with it and found that even just having the modules input ground connected to the rca cables ground was enough to make the pop even though I shouldnt have to ground the input anyway because it is already grounded through the negative power because it is a single supply.

    if I do not connect the amplifier modules ground to anything and I connect the audio signal from the rca cables to the audio input on the module then I hear a tiny bit of music but ALOT of weird distortion.


    It sounds like one of these (the stereo or the amp module) are a dual supply, but I did a test connection and both the stereos audio ground and the amp modules audio ground are just the same darn thing!
    Meaning the car batteries negative.


    HOW CAN THIS NOT BE WORKING! ITS SO SIMPLE AND YET IT IS NOT WORKING!

    help?




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    Re: Technical problem with rear speaker amplifier!

    First of all, I hope you're 13 and that's why you can't spell. That aside, can you explain why you're bringing your car's voltage supply to 20V? I honestly have never even looked into this, but pretty sure it's not this simple. Second, I am pretty sure your amp cannot operate at 20V. I think most car amps have a maximum operational voltage of 16V. There is a brand called taramps that makes amp that operate at higher voltage. You need to ditch the 20V idea and roll with 12V.




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    Re: Technical problem with rear speaker amplifier!

    All higher power car amplifiers run off of above 16v, somtimes close to a hundred volts.
    inside the chassis there is a step up dc-dc converter useing a 150khz occilating enhancement type n-channel mosfet to bias an inductor causing a swap of voltage and current keaping virtually equivalen wattage levels on both primary and secondary sides of the pulse width modulated power supply. Thats all standard opperation and inside of every car amp you will ever own.
    But I think im asking my question in the wrong place.




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    Re: Technical problem with rear speaker amplifier!

    Not trying to be argumentative, but then why do most amp manufacturers list 16V max operational voltage on their amp specs? And go as far as to say not to run the amp with 16V systems?




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    Re: Technical problem with rear speaker amplifier!

    I'm interested to see if any of the more veteran users have anything to say here. It sounds like you know what you're talking about, but I don't know how many people here would try to implement a car audio setup without car audio-specific gear. You can make things a lot easier by buying a 12-16v amp designed for this purpose.



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    Re: Technical problem with rear speaker amplifier!

    Actually alot of amps do go to 18v, but this is not the proper way to do it since the alt needs to be regulated to run at the voltage you choose.

    The way you currently are doing it you will not only fry all your electrical since this is not a 100+ volt system like your home.

    Your electrical has to be regulated from the source.




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    Re: Technical problem with rear speaker amplifier!

    Quote Originally Posted by tesladude View Post
    All higher power car amplifiers run off of above 16v, somtimes close to a hundred volts.
    inside the chassis there is a step up dc-dc converter useing a 150khz occilating enhancement type n-channel mosfet to bias an inductor causing a swap of voltage and current keaping virtually equivalen wattage levels on both primary and secondary sides of the pulse width modulated power supply. Thats all standard opperation and inside of every car amp you will ever own.
    But I think im asking my question in the wrong place.
    Not all amps can go that high. Some max out at 15v. Mine do... The amps made to run higher than 18 are mostly Brazilian and they get that higher voltage by paralleling batteries not the alternator. They are ran off batteries only.



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    Re: Technical problem with rear speaker amplifier!

    Correct me if I'm wrong here. Are you trying to run an amplifier board like the ones they sell at parts express? A little 25x2 d board and stepping the voltage up to it? My main question is it sounds like you are using a harness ground? What exactly are you using for the ground?




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    Re: Technical problem with rear speaker amplifier!

    Guys, yes car amplifiers are initially powered by a simple 12v car battery.
    I am talking about the guts, (I am an electrical engineer and have designed and made similar amps by hand,)
    Inside your amp there is a chip that simply connects and disconnects power to a large transformer or coil, on the other side of your coil you get much higher voltage which is required to power the mosfet amplifier circuit which puts out the wattage these amps put out.(That is the VERY simple way to put it.)
    (yes I know my spelling *****, don't have to be an ***.)


    I am done with this project but the 20v was referring to the voltage after the pwm step up power supply.




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    Re: Technical problem with rear speaker amplifier!

    I was grounding directly to the chassis, and no I do not trust those modules so I make my own.

    ---------- Post added at 12:04 AM ---------- Previous post was at 12:03 AM ----------

    Quote Originally Posted by garychoffmann View Post
    Correct me if I'm wrong here. Are you trying to run an amplifier board like the ones they sell at parts express? A little 25x2 d board and stepping the voltage up to it? My main question is it sounds like you are using a harness ground? What exactly are you using for the ground?




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