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Thread: Small 12v Amps (50w RMS x2 @ 8ohms)

  1. #1
    Newbie dacomputernerd's Avatar
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    Small 12v Amps (50w RMS x2 @ 8ohms)

    Hey guys,

    I'm looking for suggestions for a small 12v amp for a project. It needs to push ~50w RMS per channel @ 8ohms. Two channels is enough for my use.
    I'll take 30w-50w RMS if it's the right price. Working on a student budget.


    If they make a bridgeable 15w-25w RMS @ 4ohms amp, that would also do the trick. I'd be willing to run two amps if necessary.


    Weight and size is also a concern, hence why I just don't buy something bigger/more powerful. As is cost, as I'm on a student budget.



    Thanks!
    Last edited by dacomputernerd; 01-10-2013 at 12:05 PM.

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    FLAC SNOtwistR's Avatar
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    Could this be something that you could use? http://store.mp3car.com/TDA7850_Inte..._p/com-140.htm Just a thought SNO

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    Constant Bitrate eugenweij's Avatar
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    depending on your location, I can reccomend marquant mca200 for this , it's small, lightweight and has 2x100W peak

    I know its for sale in europe for around 20 euros , not sure about the US.
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  4. #4
    Newbie dacomputernerd's Avatar
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    Quote Originally Posted by SNOtwistR View Post
    Could this be something that you could use? http://store.mp3car.com/TDA7850_Inte..._p/com-140.htm Just a thought SNO
    That looks perfect! (except for cost) What kind of heatsink would I run on it? Can it be bridged to two channel?


    Quote Originally Posted by eugenweij View Post
    depending on your location, I can reccomend marquant mca200 for this , it's small, lightweight and has 2x100W peak

    I know its for sale in europe for around 20 euros , not sure about the US.
    I'm in Canada, and I should be able to get it shipped here. Whether it's worth the shipping charge, I'm not sure.
    Last edited by dacomputernerd; 01-10-2013 at 12:04 PM.
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    FLAC SNOtwistR's Avatar
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    Sent you a PM SNO

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    Constant Bitrate
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    FLAC PhilG's Avatar
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    Newbie dacomputernerd's Avatar
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    Is this bridgeable down to two channels? Are those wattage output levels with a 32v supply?




    I think this is a better choice.
    http://www.parts-express.com/pe/show...number=320-303

    Any idea of the power output at 14v? The quoted values are at 32v.
    It should be the same no? The amp will just draw more current at a lower voltage.
    Last edited by dacomputernerd; 01-11-2013 at 10:10 AM.
    -Electrical Engineering Student.

  9. #9
    Constant Bitrate
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    Quote Originally Posted by dacomputernerd View Post
    Is this bridgeable down to two channels? Are those wattage output levels with a 32v supply?




    I think this is a better choice.
    http://www.parts-express.com/pe/show...number=320-303

    Any idea of the power output at 14v? The quoted values are at 32v.
    It should be the same no? The amp will just draw more current at a lower voltage.
    I am unsure. You may want to check over on diyaudio forums, they'd be more knowledgeable than I.
    "You're just about as useless as JPEGs to Helen Keller" - Wierd Al

  10. #10
    Constant Bitrate
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    I would think that at the lower voltage the output power will be reduced. This is not a Switched mode power supply with a feedback loop to keep the output voltage at the desired level. Hence the "switching" Part of Switching mode power supply. An SMPS is basically a switch turning on and off really fast. If there is more load, and the voltage starts to droop, the feedback look kicks in and changes the duty cycle of the switch, to leave it in the on state for longer to bring the voltage back up.

    Amplifiers work by conducting current through an output stage that is essentially a "valve" to the bus supply. If the bus supply is 14V, and the "valve" is fully on, and the speaker is 8 Ohms, the current is 1.75A. Since power in Watts is Current Squared times resistance, then 1.75 x 1.75 x 8=25.5 Watts. If you used a 4 Ohm speaker the power would be 14V/4 Ohms=3.5A. The power in that case is 3.5 x 3.5 x 4 = 49 Watts. Also remember Watts and actual loudness are not a linear relationship. They are logrithmic. A general rule of thumb is 10 times the power for something to sound twice as loud.

    Obviously all these calcs are done using straight DC values at 100% efficiency. There is inductance and capacitance (Reactance) to consider. But these give you the general idea. To get more output, you need to increase the bus voltage. It also needs to be stiffened with some value of capacitance. A power supply is only as good as the instantaneous current it can put out. The caps help to supply these current peaks during musical peaks.

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