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Media Box -- Need Power Supply

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  • Media Box -- Need Power Supply

    I plan on throwing an Alix Board and either a Sure or ClassDaudio 50WPC amp together into a par-metal case and need help selecting a power supply.

    In Pete S.'s PCeiver, he taps power from a beefy PC power supply for his amplifier and is able to run off of a single power cable:

    http://techtalk.parts-express.com/sh...&postcount=127

    But I'm wondering if I need a traditional PC power supply for the stripped down, low power, fanless Alix board (there will be no hard drive, but there will be a sound card and wireless PCI/MiniPCI cards attached). This is what it says in their manual:

    +12V DC, ~ 0.007A off state, typical about 0.4A active
    Peak power can be higher, suggest a 15W supply.
    Center pin = positive, sleeve = ground, 2.5 mm diameter.
    http://pcengines.ch/pdf/alix1c.pdf

    The Sure amp, PE# 320-300 needs DC 10-36V, connecting via jack or terminal blocks. This is what the manual for the ClassDaudio CDA-224 amp says:

    A dual (bipolar) DC power supply of +/-30 to +/-40 Volt should be connected to the terminals V- GND V+ of the 3-position terminal block (shown in photo on following page). The minimum supply voltage is +/- 30V, and the maximum value is +/- 40V.
    So, is it possible to supply power to both boards with a single, easy to purchase and install power supply? Is there one with 2 separate DC outputs? If possible I would like to go fanless, or at least one with a fan that turns on only when hot.

    Cheers,
    - John

  • #2
    Re: Media Box -- Need Power Supply

    If you go with the Sure Amp, theoretically, you could use one beefy 12Vdc supply to power everything. But if you are planning to run the full 2 x 100W, you're talking about a 20+A supply. I don't know of any PC power supplies that will provide 20A at 12V, but there are commercially available 12Vdc supplies you could use.

    However, I think you are really better off with two supplies, for two reasons: First, the Sure amp will be more efficient with higher voltage. Second, the supply voltage to your amp(s) is going to be bouncing around with the audio load. You don't really want to subject your computer to that.

    For the computer board, just buy some cheap 12V supply (wall wart?). For Sure amp(s), build a simple 32Vdc supply. Doesn't need to be regulated. Just throw a honkin' torroidal transformer in a box with a bridge rectifier and 30 or 40 thousand uF of filter capacitance and call it good ;). With the ClassDAudio amp, you are definitely looking at a custom dual-rail power supply

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    • #3
      Re: Media Box -- Need Power Supply

      If I remember correctly Pete didn't use the PC power supply to power his ClassDaudio amp boards. He shoe-horned in the big toriod transformer and power supply board (bridge rect. with caps) that ClassDaudio supplies with their amp kits.
      Craig

      The lowest possible F3 box alignment is not always the best alignment.

      Designing and building speaker projects are like playing with adult Lego Blocks for me.

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      • #4
        Re: Media Box -- Need Power Supply

        You will need a 24-32 VDC power supply with the Sure board to get close to the rated power. A 12 VDC supply, regardless of amperage rating, will give you much lower power.

        I doubt you will find an off-the-shelf power supply to give you the +/- 30 to 40 V for the Class D amp plus 12 V for the other board. Suspect you will need two or you will have to custom build one.

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        • #5
          Re: Media Box -- Need Power Supply

          Get a DC-DC ATX converter and a 12VDC wall wart, or better yet a Linear DC Regulated Supply for the computer section.

          It is what I did for my 2.0 PC and couldn't be happier.

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          • #6
            Re: Media Box -- Need Power Supply

            I didn't read the manual, but if the Alix PC board only needs 12Vdc/0.4A I would just use a heatsinked LM7812 regulator IC, fed from the positive DC voltage rail of the power supply board. So, you would just need the ClassDaudio power supply board, a toroid, and the regulator + filter caps on a piece of perfboard.
            "I have not failed. I've just found 10,000 ways that won't work." Thomas A. Edison

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            • #7
              Re: Media Box -- Need Power Supply

              Thanks guys for the thoughts and suggestions!

              Originally posted by AJ View Post
              I didn't read the manual, but if the Alix PC board only needs 12Vdc/0.4A I would just use a heatsinked LM7812 regulator IC, fed from the positive DC voltage rail of the power supply board. So, you would just need the ClassDaudio power supply board, a toroid, and the regulator + filter caps on a piece of perfboard.
              This is the one I like best. I was leaning toward the ClassDaudio anyway. Although more expensive than the Sure, I think it would have better SQ. Just compared the THD numbers, and the ClassDaudio looks a lot better. The webpage on the CDA-254L (the kit with the larger power supply) says there is enough juice to power 2 amps. So this seems to be the logical choice.

              http://classdaudio.com/products/clas...ansformer.html

              I found this diagram for the LM78XX regulators. As ignorant of electronics as I am, I think I should be able to handle this.

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              • #8
                Re: Media Box -- Need Power Supply

                Originally posted by jclin4 View Post
                I found this diagram for the LM78XX regulators. As ignorant of electronics as I am, I think I should be able to handle this.
                I wouldn't use a linear regulator. With a typical flow of .4A and a voltage drop of 18V (30V - 12V), you are going to be dissipating about 7W from that regulator. That's not a big problem for a big heatsink, but if you use a 40V source you are getting up in the 12W range, and getting close to the maximum rating of the LM78XX. A small switching regulator with 12V output would be a better choice.
                Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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                • #9
                  Re: Media Box -- Need Power Supply

                  I found this diagram for the LM78XX regulators. As ignorant of electronics as I am, I think I should be able to handle this.
                  Just don't forget the heatsink, as AJ mentioned. If your + rail is 36Vdc you will be dropping 24V @ 400mA in the regulator. That's nearly 10W. You'll need a heatsink with 3C/W or better (performance). That's not a small chunk of aluminum.

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                  • #10
                    Re: Media Box -- Need Power Supply

                    Just a thought, couldn't you wire up two 12V power supplies in series to double the voltage?
                    Modding the Lepai T-Amp

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                    • #11
                      Re: Media Box -- Need Power Supply

                      I was going with +/-30Vdc in mind. You can't put more than 35V into these regulators, unless you get creative. You could use a pass transistor, like a 2N3055 mounted to the case to supply the current, but that's starting to get more complicated for a beginner in electronics. I could provide a schematic if you wanted to try it though.

                      Simplest way would be to find a small 12V/1A SMPS and just stick it in your case.
                      "I have not failed. I've just found 10,000 ways that won't work." Thomas A. Edison

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                      • #12
                        Re: Media Box -- Need Power Supply

                        I just took a closer look at ClassDaudio's smaller power supply board, and it is 48 volts! So it looks like the linear regulator route is out of the question. :(

                        So I looked for a small switching regulator with 12V output and found this:



                        http://parts.digikey.com/1/parts/630...m-12-nopb.html

                        But the number of connections and diagram of typical applications in the spec sheet are scaring me :rolleyes:

                        So looks like I may just run a wall wart into the media box along with a separate power supply (toroid and board) for the amp.

                        Thanks guys for the additional input

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                        • #13
                          Re: Media Box -- Need Power Supply

                          How about something like this?

                          http://search.digikey.com/us/en/prod...884-ND/2057033

                          It's only 3.1"/2"/1.1", so you should be able to fit it in your case. It's more expensive, but IMO a better solution than running a wall wart. It's got more than double the capacity you actually need, but it's the cheapest I could find at digikey.
                          "I have not failed. I've just found 10,000 ways that won't work." Thomas A. Edison

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                          • #14
                            Re: Media Box -- Need Power Supply

                            Originally posted by AJ View Post
                            How about something like this?

                            http://search.digikey.com/us/en/prod...884-ND/2057033

                            It's only 3.1"/2"/1.1", so you should be able to fit it in your case. It's more expensive, but IMO a better solution than running a wall wart. It's got more than double the capacity you actually need, but it's the cheapest I could find at digikey.
                            Hey that solution is looking very good! I agree that it seems to be a better solution than a wall wart, not from a technical perspective (which I am not qualified to evaluate), but from a usability and simplicity of deployment perspective, which is what I was going for in trying to get a single power cord into the box.

                            Thanks again AJ

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                            • #15
                              Re: Media Box -- Need Power Supply

                              A typical wall wart is just a transformer, bridge rectifier, and a filter cap. So it's just a linear, un-regulated, DC power source. They usually don't have enough filtering and are usually over-speced current wise. Most "12V" rated ones will have an unloaded output of 14-15V because of the terrible load regulation of the tiny transformers they use. They serve their purpose for some stuff, but a good SMPS would be better for this application, since you can't use a standard regulator IC without it getting complicated with your ~ 50V rails.

                              Some (like laptop power bricks) are switch-mode supplies, not unlike the one I suggested above. If you could find one like that with a 12V output that would work fine too.
                              "I have not failed. I've just found 10,000 ways that won't work." Thomas A. Edison

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