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Thread: How do I change a computer power supplt to give me + - 35v @ about 4amps per rail????

  1. #1
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    Post How do I change a computer power supplt to give me + - 35v @ about 4amps per rail????

    I would like to modify a computer supply to use it to power a amplifier instead of using a chunky, expensive transformer.. I need about + - 35volts at about 4amps each, and help would be greatly appreciated... thanx..

    Or, does someone know of a switchmode circuit able to deliver this sort of power??

    [ 09-27-2001: Message edited by: SkinnyBoy ]

  2. #2
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    Originally posted by SkinnyBoy:
    <STRONG>I would like to modify a computer supply to use it to power a amplifier instead of using a chunky, expensive transformer.. I need about + - 35volts at about 4amps each, and help would be greatly appreciated... thanx..

    Or, does someone know of a switchmode circuit able to deliver this sort of power??

    [ 09-27-2001: Message edited by: SkinnyBoy ]</STRONG>

    Switched mode supplies are most often frowned upon as they contaminate the sound output with their switching noise. Anyway it would be easier to design your own +/- 35V supply than to modify an AT/ATX one.

    Presslab

  3. #3
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    I suppose you could find the power supply lead that runs 12 volts and transform that up to 35, but I don't know if a computer power supply will be willing to put out 4 amps. I'm assuming you want DC power, why not just transform the 12 volt from the car into 35 volts with a homemade transformer?
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    Okay, I probably should have said that this isn't for the car, its for in the house, and I realize that modifying would be harder than creating, but to create one, you might not be able to get all the parts...

  5. #5
    Retired Admin Aaron Cake's Avatar
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    Modifying a computer supply is not going to work.

    Instead, build a large linear supply. You probably don't really even need regulation, so you could get by with a large transformer, rectifier and some filter capacitors. The most difficult thing to find will be the transformer, but you can make your own very easily. Simply get an old microwave transformer, remove the secondary, and wind on your own center tapped 70V secondary. After that, follow standard power supply procedures, making sure to include lots of filtering.
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    I don't want to use a transformer, thats the whole point.....
    I can't afford it, its too big, and , and well, I wanted to make the amp as small as possible.. so, what I am asking, is, does anyone know of a switchmode power supply circuit diagram, that can be easily changed to sute my requirements???

  7. #7
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    Originally posted by SkinnyBoy:
    <STRONG>I don't want to use a transformer, thats the whole point.....
    I can't afford it, its too big, and , and well, I wanted to make the amp as small as possible.. so, what I am asking, is, does anyone know of a switchmode power supply circuit diagram, that can be easily changed to sute my requirements???</STRONG>
    it can't work. If you want to change a supply to put out -35 instead of -12 (or 35 instead of 12) you will have to change the feed back windings of the transformer to get the right amount of voltage. plus, there is a chance the parts aren't rated for 35 volts. If you were a power supply designer and you wanted to choose caps to put on the outputs of your 12 volt supplies, would you choose caps rated at 50 volts? No, you would choose caps rated at 25 volts maybe 35 volts. So even if you could modify the supply so the feedback loop would try to put out twice the voltage by changing a simple resistor, your supply would fail. You can go to www.astec.com and order a supply that is rated for your needs, or you can go to a garage sale, pick up a 1990's Sony 100W amp (which has the +- 35 volt rails at your whopping 4 amps) and be nice a happy with the transformer. Or, you can wait until Hell=FrozenOver and have someone give you one or find one at a surplus store. You just have to keep your eyes open.

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    OKAY!!!!
    I don't want to modify a power supply, I want to make one from scratch, does and know of a website with a diagram???

  9. #9
    FLAC
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    What input voltage? You want 120 in AC, + - 35 DC out? No transformers?

    Can you do inductors?

    How about this, use a diode, a 21 ohm 340 watt resistor and you got +35 @ 4 amps from the wall.

    Oh you want to do it right? Go to the library! Get the ARRL handbook. Read up on circuit stuff. Then get a book called switch mode power supplies.

    Then your set. Get a degree in EE and your on your way to all the +- 35 volt power supplies you want. There is NO EASY ANSWER where someone says, yaa just hook up a transistor and a diode. You will need to know what your doing unless you find something that someone has designed. Chances are you won't find it. I've looked.

    Feel free to prove me wrong though. :-)

    Jeff
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  10. #10
    Constant Bitrate
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    Also,I think you will need a circuit to prevent click-on-start and shutdown,if you don't want to blow your speakers.
    Enjoint life!

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