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I have a question about power supply requirements

Discussion in 'Power Electronics' started by James Watt, May 29, 2017.

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  1. James Watt

    James Watt

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    Jul 20, 2016
    I'm setting up a 12v bluetooth amp in my shop. I'm told that the power leads are ground and a 3 amp fused line. I'm wondering if I can use a standard 12v "wall wart" type of power block and if so should it provide 3 amps or more? If more, how much? Thanks in advance to anyone who can help me out.
     
  2. Audioguru

    Audioguru

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    Sep 24, 2016
    If the 12V amp has a 3A fuse then it can be powered from a 12V at 3A or more power supply. If the power supply is a cheap wall wart then the amp will probably produce hum.
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    A fuse with a nominal value of 3 A indicates that the typical current consumption is even less. A 3 A wall wart should suffice.

    Do not take @Audioguru 's warning lightly: Moderns wall warts use switch mode technology which inherently creates high frequency noise on the output. This noise may (or may not) lead to audible interference in the amplifier. Additional filtering may be required (unless the amplifier has a good internal filter which may well be the case if it was designed for use with such wall warts).
     
  4. James Watt

    James Watt

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    Jul 20, 2016
    Thank you both for your help! The amp that I chose is designed for off road or marine use and therefore would typically be connected to a an auto/marine battery. I'm setting it up in a wood shop in hopes that it can survive the dusty environment. In the event that the wall wart power supply does produce a hum, what would you recommend as a more suitable power supply? I need it to be impervious to (or at least unaffected by) the dust, and I'm trying to keep it as inexpensive as is practical, but I definitely want the best sound possible.
     
    Last edited: May 30, 2017
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Start with the ower supply you were going to buy anywhere.
    If there is a hum, get an automotive dc power supply filter like e.g. this one. Don't waste the money for the filter without first trying the wall wart alone.
     
  6. James Watt

    James Watt

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    Jul 20, 2016
    Thanks again for the information. Yes, I've already ordered a wall wart and will try it first. In the event that it's not suitable and as another alternative to adding the filter that you recommend, are there wall warts available that include a filter?
     
  7. Audioguru

    Audioguru

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    I think a filter costs money so if the wall wart is a cheap one then it has a poor filter.
     
  8. James Watt

    James Watt

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    Jul 20, 2016
    @Audioguru So then I guess I can assume that there are wall wart power adapters that include adequate filters, but that they would be a bit more expensive. I'm OK with spending a little more in order to keep the set up simple. How can I know if a power adapter has an adequate filter?
     
  9. Audioguru

    Audioguru

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    Sep 24, 2016
    When I design an amplifier then I make it have its own filter so that it works fine with almost any power supply. But I don't buy cheap power supplies from ebay.
     
  10. James Watt

    James Watt

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    Jul 20, 2016
    @Audioguru I'm not designing an amplifier, I'm simply trying to determine what is a suitable power source for the amplifier that I plan to use. As I said, I'm OK with spending a little more on a power supply in order to keep the set up simple. So my question was... are there wall wart power adapters that have the necessary filter and how can I be sure that the adapter I order has an adequate filter?
     
  11. Audioguru

    Audioguru

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    Sep 24, 2016
    The biggest most powerful wall-wart I have produces 12V/1A with a fairly large low frequency transformer. I have tiny lightweight 5V/2A switched mode high frequency power supplies but their voltage is too low for my amplifiers so I do not know if they produce noises.

    Your amp needs 12V at almost 3A which will be too big and heavy if a wall wart has a low frequency transformer so you probably will not find a wall-wart for it. There are many 13.8V/3A to 5A well filtered power supplies that would be suitable for you that have a cord that plugs into the wall electricity and are designed to power a car radio.
     
  12. James Watt

    James Watt

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    Jul 20, 2016
    Thank you for this information. Is the 13.8A 3-5V power supply that you refer to similar to one that would act as a charger/power supply for a laptop computer?
     
  13. Audioguru

    Audioguru

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    Sep 24, 2016
    I think many laptops use a 19V power supply. A car radio uses a 13.8V power supply.
     
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