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

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  • 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
    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

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    • #3
      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?
      Mp3car setup on the way... it's gonna run like this:
      5" TFT LCD running out of a 32 MB 4x AGP GeForce 256, on a 667 MHz Celeron and a 4.3GB Hard Drive, running linux and probably MS98 solely for the purposes of Diablo II.
      Also a playstation 1, and my stereo:
      2 Rockford Fosgate 360a2 (1 punch, 1 power) running 4 10" subs.
      1 RF punch 120a2 running 2 Jensen 6x9s in boxes
      Custom box (it looks cool. pics someday)
      4 ga. & 8 ga. power
      10 ga. speaker wire all around
      16' RF shielded RCA
      Pioneer 1100DEH (until I get a MP3car)

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      • #4
        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...

        Comment


        • #5
          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.
          Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
          Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
          "If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

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          • #6
            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???

            Comment


            • #7
              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.

              I got a Mag 17 inch monitor 4 years ago for 100 bucks because they thought it was broken. at the time it was a 800 dollar monitor.
              MPEGBOX - Plexiglass Computer
              www.mpegbox.com

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              • #8
                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???

                Comment


                • #9
                  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
                  MPEGBOX - Plexiglass Computer
                  www.mpegbox.com

                  Comment


                  • #10
                    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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                    • #11
                      Also,I think you will need a circuit to prevent click-on-start and shutdown,if you don't want to blow your speakers.
                      I've got a circuit that does that, the speaker output isn't switched on untill the amp has been powered for about 5seconds..

                      So, no-one knows a site or has a diagram lying around for a switchmode power supply?? okay..

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                      • #12
                        like Jeff said, for alot of things around us there are not easy answers......


                        ....most ppl know this at one point or another, I like to call this "life"....

                        (not a grinning smart-arse smile... just a refelction to what I wrote)
                        Project - GAME OVER :(

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                        • #13
                          Not my web page, but something to look at

                          Go there, look on the bottom of the page. It is linear, unregulated, basic. Adding a regulator to it will increase your overall power supply rejection ratio (PSRR), hence lower 60hz noise. It is not small, but it is simple.

                          If you're really bent on using a switching supply, good luck!

                          Transformer basics

                          Go there, and learn how to wind your own transformer. I recommend a toroidal as they have the least EMI (good for audio).

                          If this is for home use, the size difference from a linear regulator vs switching is not really a big deal. It will be quite a bit heavier though.

                          Presslab

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                          • #14
                            No matter what power supply you build, you will need a transformer. It's that simple. Switching power supplies are much harder to build than linear units, so not many people even bother to design them for hobbiest situations. Best bet would be to buy one on the surplus market.
                            Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
                            Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
                            "If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

                            Comment


                            • #15
                              Well, okay...
                              could someone tell me then, how to modify a computer power supply so that the 12volts is 3 times the voltage??? It can be done right???

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