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Help with power supply hum

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  • #16
    Originally posted by devnull View Post
    If I'm understanding this correctly the hum starts when you hook up the DC-DC convertor without the bluetooth board. It's possible that the hum is caused because the DC-DC convertor isn't under load.

    Does it still hum if you hook up the bluetooth board without the audio cables?
    Does it still hum if you hook up the bluetooth board and the audio cables?

    See post #7 for a quick fix. In fact just skip the cap and use a 7812 on the output of the power supply to drive the bluetooth board. Just pull one from an old PC power supply to try it.

    As an aside after looking at the specs for the DC-DC convertor and the bluetooth board the convertor doesn't meet the spec for the minimum current Sure specs for the bluetooth board
    I was trying to figure out how much power he was getting to the speakers after drawing off power for the dsp and bluetooth board. How did you figure power consumption for the BT board?
    http://techtalk.parts-express.com/fo...khanspires-but
    http://techtalk.parts-express.com/fo...pico-neo-build
    http://techtalk.parts-express.com/fo...ensation-build

    Comment


    • #17
      this is the bluetooth board - https://www.parts-express.com/sure-e...SABEgJH_fD_BwE

      and these are the amps - https://www.parts-express.com/sure-e...-only--320-332

      that particular bluetooth unit works perfectly, i have no complains, audio is perfect. have built so many units with out a hitch...until now that is. with this new power supply problem.

      the bluetooth module is 12, cant power it direct with 19v

      ive used the new power supplies on existing builds and they hum. when i swap out with the old ones, ZERO hum. im just building copies if what i already know works.

      power requirements were trial and error. but got them figured out and they work just fine. until now.

      the bluetooth unit has no hum when powered by 12V standalone.

      the minidsp and 2 amp combo work flawlessly off 19V power supply. more clean power than the speakers can handle. zero distortion.



      currently, the hum develops when i connect the dc-dc convertor (its wired directly, no caps, nothing), just soldered on a piece of veroboard and directly tapped from the 19 volt line and output to the bluetooth unit. proximity makes no difference.

      ive got it laid out in front of me. using the PE power supply (or others that ive bought recently to test,.. it hums), using the older power supply, no hum.

      im not sure re the 7812 converter. would this one work? https://www.amazon.com/Chironal-Step-down-voltage-regulator-rectifier/dp/B07G9HBYCB

      would it eliminate the hum?

      this - ?
      https://www.amazon.com/Stayhome-Volt.../dp/B07PM4X449





      thanks again for the help.

      Comment


      • #18
        Originally posted by Kornbread View Post

        I was trying to figure out how much power he was getting to the speakers after drawing off power for the dsp and bluetooth board. How did you figure power consumption for the BT board?
        The page at parts express shows 12V @ 1 amp. PG02S2412A shows a minimum draw of 42mA and a max of 167 mA. I don't think Sure would have specd the current draw at 6 times what it really is.

        I just wonder if the hum is reflected current ripple from the device from the device, especially under no load getting through the power supply filters on the DSP and/or the amp or else the power supply might not be able to keep up switching wise with the varying load from the DC-DC converter switching.

        And that's why I suggested an old school 12V regulator.

        Comment


        • #19
          The DC-DC converter is needed for the BT module at 12 V (i.e., different voltage than the amps' voltage). That's because DC based units at different voltages will have a different "0" for their signals (i.e., the half voltage of the 0 to PS+ V will be different and cause ground loop hum).

          I might try a simple PS bypass cap on the input and/or output to the DC-DC converter. A large value (e.g., 1,000+ uf) and a small value (e.g., 1 uf) in parallel if you have caps lying around.

          In the absence of spare caps, I'd try taking the PS for the Dc-DC converter off one or the other the Sure amps. They have some beefy PS bypass caps on board and most Sure amps have 2 PS inputs (plug and screw terminal directly connected to the on board caps).

          Lastly, has the physical configuration of unit change? There are issues with two separate class D amps in proximity. Different orientations, wiring paths, etc.

          Comment


          • #20
            Just try something like this. You need plain and simple since you're already starting out with DC from the power brick. The input and output filter caps are optional IMO.

            https://www.parts-express.com/7812--...r-to-220--7812

            Comment


            • #21
              Originally posted by devnull View Post
              Just try something like this. You need plain and simple since you're already starting out with DC from the power brick. The input and output filter caps are optional IMO.

              https://www.parts-express.com/7812--...r-to-220--7812
              isnt this sort of the same thing as i have already been using?

              https://www.mouser.com/ProductDetail...52BUjKhQ%3D%3D

              i'll try it, theres pre built ones i linked to on amazon. those have caps on it.
              just trying to understand the logic behind it.
              i will just have to assume some power adapters have a better filtered output than others. cant explian why some power supplies have the switching frequency hum and other dont.
              anyhow, have to work the problem.
              i like the idea of tapping a filtered output from the sure amp. this is the on ei use. will look at it later today and see. https://www.parts-express.com/sure-e...-only--320-332

              again, thanks all who have chimed it to help me with this conundrum.


              asmd.

              Comment


              • #22
                Originally posted by asmd View Post

                isnt this sort of the same thing as i have already been using?

                https://www.mouser.com/ProductDetail...52BUjKhQ%3D%3D

                i'll try it, theres pre built ones i linked to on amazon. those have caps on it.
                just trying to understand the logic behind it.
                i will just have to assume some power adapters have a better filtered output than others. cant explian why some power supplies have the switching frequency hum and other dont.
                anyhow, have to work the problem.
                i like the idea of tapping a filtered output from the sure amp. this is the on ei use. will look at it later today and see. https://www.parts-express.com/sure-e...-only--320-332

                again, thanks all who have chimed it to help me with this conundrum.


                asmd.
                The standard 12 V 7812 regulator is not isolated. Neither are the step-down buck regulators. Your DC-DC converter is isolates the source PS from it's 12 V output. That eliminates ground loop (hum) between the modules. Try the Sure amp output as that is an easy and quick test.

                Comment


                • #23
                  Originally posted by Millstonemike View Post
                  The DC-DC converter is needed for the BT module at 12 V (i.e., different voltage than the amps' voltage). That's because DC based units at different voltages will have a different "0" for their signals (i.e., the half voltage of the 0 to PS+ V will be different and cause ground loop hum).

                  I might try a simple PS bypass cap on the input and/or output to the DC-DC converter. A large value (e.g., 1,000+ uf) and a small value (e.g., 1 uf) in parallel if you have caps lying around.

                  In the absence of spare caps, I'd try taking the PS for the Dc-DC converter off one or the other the Sure amps. They have some beefy PS bypass caps on board and most Sure amps have 2 PS inputs (plug and screw terminal directly connected to the on board caps).

                  Lastly, has the physical configuration of unit change? There are issues with two separate class D amps in proximity. Different orientations, wiring paths, etc.

                  nothings changed. absolutely nothing.
                  only a different power supply.
                  even the unit PWR+ sells now to replace the previous discontinued one, same specs and everything hums. Previous one didnt.

                  if i plug the PE power supply/newer PWR+ power supply/DTK etc etc to a previous build, it hums. i use the old PWR+ power supply, it does not. (if i use the DELL power supply it doesnt either)

                  thats what i dont get.

                  Comment


                  • #24
                    Originally posted by asmd View Post


                    nothings changed. absolutely nothing.
                    only a different power supply.
                    even the unit PWR+ sells now to replace the previous discontinued one, same specs and everything hums. Previous one didnt.

                    if i plug the PE power supply/newer PWR+ power supply/DTK etc etc to a previous build, it hums. i use the old PWR+ power supply, it does not. (if i use the DELL power supply it doesnt either)

                    thats what i dont get.
                    All these amps and PSs use higher switching frequencies though none of the frequencies are "defined standard". You could be getting interaction between the high frequencies with certain combos (e.g., the amps and the PS). Do the quiet PSs have that "bulge" just before the plug? That's to reduce switching frequency from getting through the PS feed.

                    Comment


                    • #25


                      OK. so after some tinkering, im still at square one.
                      the two power inputs for the sure amp are the same. they dont run through any filtering caps. doesnt matter, hum still present with the PE power supply. (connected power in through DC jack and slaved power off the screw terminals. )
                      The old PWR+, Dell and PE power supplies all have the bulge,

                      the only that work, are the old Pwr+ and the DELL.
                      Havent found any others that work without that switch hum.,

                      since the DC-DC converter i used is isolated, this would not be a ground loop would it?

                      as to adding caps to filter the power "in" and "out" of the DC-DC converter, how would i go about doing that?

                      still looking for a solution... and why this is happening to some power supplies and not others,.


                      how have folks here dropped DC voltage successfully without introducing a hum?


                      looking forward to replies.

                      asmd.

                      Comment


                      • #26
                        You're getting some weird interaction between the new power supplies and the DC-DC convertor. I'm not even gonna speculate any more on what's actually causing it.

                        The DC-DC convertor you're using is not the same as a 7812 voltage regulator. You're using an active device that has a higher efficiency than a plain voltage regulator which dissipates the excess power as heat.

                        You shouldn't have to worry about floating grounds, signal grounds, chassis grounds and the halfway point between GND and Vcc. From a quick look at the schematics everything is referenced off of GND, which in this case should be 0 volts.

                        So if everything is based off of a common ground you don't need a fancy device to make your 12 volts for the bluetooth board. A simple 7812 regulator should do what you need. At this point why not try it? It's a lot cheaper than trying and buying power bricks,

                        BTW, Sure does make a 30 watt amp with bluetooth built in which would eliminate having multiple boards and extra voltage regulation.

                        Comment


                        • #27
                          Originally posted by devnull View Post
                          You're getting some weird interaction between the new power supplies and the DC-DC convertor. I'm not even gonna speculate any more on what's actually causing it.

                          The DC-DC convertor you're using is not the same as a 7812 voltage regulator. You're using an active device that has a higher efficiency than a plain voltage regulator which dissipates the excess power as heat.

                          You shouldn't have to worry about floating grounds, signal grounds, chassis grounds and the halfway point between GND and Vcc. From a quick look at the schematics everything is referenced off of GND, which in this case should be 0 volts.

                          So if everything is based off of a common ground you don't need a fancy device to make your 12 volts for the bluetooth board. A simple 7812 regulator should do what you need. At this point why not try it? It's a lot cheaper than trying and buying power bricks,

                          BTW, Sure does make a 30 watt amp with bluetooth built in which would eliminate having multiple boards and extra voltage regulation.

                          already ordered this one, arriving tom to try and see. LM2596.



                          i also need a 12v supply to power a vumeter board etc.
                          Also, for all my builds, each sure bluetooth module is programmed to broadcast/pairing a custom name.
                          i use 4 channels. the sure amps with built in bluetooth is a little overkill. 2 x 2 amps with bluetooth etc.
                          crossing my fingers the lm2596 module solves the problem. will know tomorrow.


                          now im wondering if i need to regulate both +12 and -12 with something like a 7812/7912 module.....
                          what does the ground (0V) do in a dual power supply output (both +/- regulated?)

                          asmd.

                          Comment


                          • #28
                            Originally posted by asmd View Post


                            OK. so after some tinkering, im still at square one.
                            the two power inputs for the sure amp are the same. they dont run through any filtering caps. doesnt matter, hum still present with the PE power supply. (connected power in through DC jack and slaved power off the screw terminals. )
                            The old PWR+, Dell and PE power supplies all have the bulge,

                            the only that work, are the old Pwr+ and the DELL.
                            Havent found any others that work without that switch hum.,

                            since the DC-DC converter i used is isolated, this would not be a ground loop would it?

                            as to adding caps to filter the power "in" and "out" of the DC-DC converter, how would i go about doing that?

                            still looking for a solution... and why this is happening to some power supplies and not others,.


                            how have folks here dropped DC voltage successfully without introducing a hum?


                            looking forward to replies.

                            asmd.
                            The bulge is called a choke and that's another name for a filter. In the case of the switching PS, it filters any remnants of the PS switching frequency from reaching the load.

                            Now your starting to lose me. Why do you need -12V? And the 12 V regulator module you ordered is not isolated and will likely cause additional noise.

                            Lastly, try a test. Disconnect the BT module (power and feed) and supply the sure amp(s) with a wired source (cell headphone out, PC line out etc.) if you still have hum, then its the Sure amps interacting with the switching PS.

                            Comment


                            • #29
                              The bulge at the end of the PS feed is called a choke. That's another name for a filter and it's used to eliminate the PS switching frequency from the load.

                              Try a test. Disconnect the BT and miniDSP modules (feed and PS) and drive the sure amps directly with a wired source (cell headphone output, PC line out, etc.). If you still have the hum, then it's the PS switching frequency leaking through to the Sure amps possibly interacting with the Sure switching frequency to produce a low hum (like the drone of a twin engine airplane overhead). If there's no hum, then add the miniDSP and drive its inputs with the wired source. This is how to logically breakdown the circuit to determine the source of the proble.

                              The buck regulator you purchased is not isolated. That's likely to introduce additional noise in the form of a ground loop with the BT module and the mini-DSP.

                              Comment

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