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  • KAB-250v3 standby whine

    I've got the KAB-250v3 and DSPB-100 connected to create a 2.1 system, but there's significant whine / hum on standby.

    I bought the power supply from Parts Express and it makes no difference over a cheap 24V/5A Chinese unit I already had laying around.

    P/E refunded and sent me new amps after I told them all the troubleshooting I went through, but they make the same exact while / hum.

    The power supply doesn't have a ground, so I can't try doing any of the ground loop fixes, like with a set of diodes inline.

    Here's a recording of it in case that helps diagnose it: https://photos.google.com/share/AF1Q...ZfWXRKcWJiWmhB

    This is the last thing to dial in for this system and I'd really like to get it resolved before giving up on it and going a different route for powering it.

    Thanks for any help!
    -Josh

  • #2
    I can't hear the wine in your photo-video. So my first guess is ground loop. That would be a fairly low note - 60 Hz whine.

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    • #3
      I don't think that's a defect, but it isn't really a feature either. When the signal stops via YouTube on the OSFA I just built, there is a pitch present until signal resumes. This is via bluetooth mainly.

      Later,
      Wolf
      "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
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      • #4
        Originally posted by Millstonemike View Post
        I can't hear the wine in your photo-video. So my first guess is ground loop. That would be a fairly low note - 60 Hz whine.
        I tried frequency matching it and it's around 120hz.
        The whine is pretty audible with headphones on listening to the video.


        Originally posted by Wolf View Post
        I don't think that's a defect, but it isn't really a feature either. When the signal stops via YouTube on the OSFA I just built, there is a pitch present until signal resumes. This is via bluetooth mainly.

        Later,
        Wolf
        I'll try using the 3.5mm jack as the source and see if it has the same issue.
        Interestingly, I can also hear a noise that coincides with the bluetooth light flashing when trying to pair.

        Thanks for the feedback. I might just send it all back if I can't sort it since it's for a set a friend had me build and he'd go nuts with that whine.

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        • #5
          In the U.S. that's a harmonic of our (60Hz) AC line frequency.

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          • #6
            Since you mentioned you're using it over bluetooth, I'll add that I've had some bluetooth sources that are a LOT worse than others. If you have a chance to test other sources that might be worth checking. Though I'm guessing your phone is a common source and I don't think I've noticed much problems from my phone over BT. Mainly it's been a specialty little BT-sender/converter that I've used to make older devices send wireless that seems to always make the KAB (a 230 in my case) whistle pretty noticeably.

            Or maybe it might it be as simple as shielding the little amp with a metal case (aside from the BT antenna of course)?
            My first 2way build

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            • #7
              I whant to use the same setup in a portable bluetooth speaker... You can hear de noise pretty good, I assume it's the Kab 250? You can try the kab-230... I read somewhere on the internet that the kab-250 had to much gain so they chose the 230.( don't know much about electronics but it's some information about it 😅). Maybe it's fixable with the dspb board settings..

              Comment


              • #8
                Originally posted by Chris Roemer View Post
                In the U.S. that's a harmonic of our (60Hz) AC line frequency.
                I thought of that, too, as I was writing out the frequency.
                I'm going to see if I can use a power conditioner to see if it has any effect.

                Originally posted by LOUT View Post
                Since you mentioned you're using it over bluetooth, I'll add that I've had some bluetooth sources that are a LOT worse than others. If you have a chance to test other sources that might be worth checking. Though I'm guessing your phone is a common source and I don't think I've noticed much problems from my phone over BT. Mainly it's been a specialty little BT-sender/converter that I've used to make older devices send wireless that seems to always make the KAB (a 230 in my case) whistle pretty noticeably.

                Or maybe it might it be as simple as shielding the little amp with a metal case (aside from the BT antenna of course)?
                I've tried my laptop and iPhone 6S and they both produce the same sound through BT, so my guess is it's not the source since they don't create any other hum like that with other BT speakers I have.

                Originally posted by Scarface1 View Post
                I whant to use the same setup in a portable bluetooth speaker... You can hear de noise pretty good, I assume it's the Kab 250? You can try the kab-230... I read somewhere on the internet that the kab-250 had to much gain so they chose the 230.( don't know much about electronics but it's some information about it 😅). Maybe it's fixable with the dspb board settings..
                That's an interesting theory.

                I've actually had two different setups and they both have the same hum.

                The first was the KAB250v3 + DSPB 100 and the second one is the opposite with the DSPB250v3 + KAB 100.

                The 100 units also hum through the sub in both cases.

                I'm going to try the 3.5mm input and see if the hum disappears.

                But, that means the BT won't be paired and that leaves it in pairing mode, which causes a secondary hum when the light goes on and off.



                Comment


                • #9
                  Originally posted by dead_end View Post

                  I thought of that, too, as I was writing out the frequency.
                  I'm going to see if I can use a power conditioner to see if it has any effect.



                  I've tried my laptop and iPhone 6S and they both produce the same sound through BT, so my guess is it's not the source since they don't create any other hum like that with other BT speakers I have.



                  That's an interesting theory.

                  I've actually had two different setups and they both have the same hum.

                  The first was the KAB250v3 + DSPB 100 and the second one is the opposite with the DSPB250v3 + KAB 100.

                  The 100 units also hum through the sub in both cases.

                  I'm going to try the 3.5mm input and see if the hum disappears.

                  But, that means the BT won't be paired and that leaves it in pairing mode, which causes a secondary hum when the light goes on and off.


                  I'm curious about that to, strange thing about the bluetooth and the 3.5 plug. That means that you can't use the 3.5 because the unconnected bluetooth will hum, so why they attached it on the board? 🤔😁

                  Comment


                  • #10
                    Originally posted by dead_end View Post

                    I thought of that, too, as I was writing out the frequency.
                    I'm going to see if I can use a power conditioner to see if it has any effect.



                    I've tried my laptop and iPhone 6S and they both produce the same sound through BT, so my guess is it's not the source since they don't create any other hum like that with other BT speakers I have.



                    That's an interesting theory.

                    I've actually had two different setups and they both have the same hum.

                    The first was the KAB250v3 + DSPB 100 and the second one is the opposite with the DSPB250v3 + KAB 100.

                    The 100 units also hum through the sub in both cases.

                    I'm going to try the 3.5mm input and see if the hum disappears.

                    But, that means the BT won't be paired and that leaves it in pairing mode, which causes a secondary hum when the light goes on and off.


                    Maybe because of this?
                    Attached Files

                    Comment


                    • #11
                      So, I ended up returning the two KAB boards as the Bluetooth hum at idle was too much for me while working.
                      The second I would pause Spotify, my speakers would just hum and distract me.

                      I ended up with two DSPB boards (100 and 2x50), so I hacked them to make a pretty decent desktop amp setup.

                      Since they only have 3.5mm inputs, I wired them into the same 3.5mm jack to send them the same signal.

                      The pots on the boards are super useful, but they're worthless without being accessible in a case. So, I wired a 10kohm pot from each one to the front panel to control volume independently between my mains and a sub. (FaitalPro 3" in a TQWT and TB6.5 vented).

                      Stacking them on a bracket with standoffs is nice and tight, but it made connecting the power to the bottom board impossible. So, I soldered solid wire from the bottom board to the top for power.

                      Finally, since they don't have a power switch available, I wired the positive inline with a rocker switch and mounted it to the front panel, below the volume pot knobs.

                      To be honest, I'm really pleased with the end result since the DSP and SigmaStudio worked so well, but am quite frustrated with all the mods I had to make and wish it had a digital input instead of just the 3.5mm jack.

                      Here's my list of what's missing to make these more useful:
                      1. Power switch
                      2. Relocatable pots
                      3. Digital input
                      4. Better power ports for mounting on standoffs
                      5. Bluetooth

                      Happy to take some pics of it all if it's useful for anyone.
                      Last edited by dead_end; 06-12-2020, 02:59 PM.

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