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    Computer speakers - fixing hum

    I've had these brand X speakers for >20 years - great sound, thought they were worth hanging onto

    But they've been developing a bad hum, which has been getting worse, until now it overpowers the sound

    Would replacing any or all of its six capacitors maybe fix the problem ?
    - 4700uf 25v - two of
    - 33uf 16v - two of
    - 1uf 63v - two of
    Attached Files
    better to keep quiet and be thought a fool, than to open your mouth and remove all doubt

    #2
    Re: Computer speakers - fixing hum

    I would look at the Power Supply section and change-out the big e-caps.....Yes probably those 2 e-caps 4700uf 25V are the problem....

    Comment


      #3
      Re: Computer speakers - fixing hum

      change the lot.

      Comment


        #4
        Re: Computer speakers - fixing hum

        Also check for bad solder joints on the input jacks.

        Originally posted by Andrew F. Ali View Post
        I would look at the Power Supply section and change-out the big e-caps.....Yes probably those 2 e-caps 4700uf 25V are the problem....
        +1

        Though, you might as well change all of the other electrolytic caps then, as stj suggested. They won't be nearly as expensive as the two 4700 uF 25V units.

        Another thing worth mentioning is that, depending on the output voltage of the transformer, you may use a linear regulator to feed the amplifier. When you do that, this should eliminate pretty much all of the hum. Something like a 7812, 7815, or 317 (adjustable) should be fine, so long as you put a proper heatsink on it and don't exceed its specs. But this suggestion is perhaps more fitting if you like playing with amps an audio gear.

        Comment


          #5
          Re: Computer speakers - fixing hum

          curious if there's hum when no signal is presented?

          Comment


            #6
            Re: Computer speakers - fixing hum

            Originally posted by momaka View Post
            Also check for bad solder joints on the input jacks.


            +1

            Though, you might as well change all of the other electrolytic caps then, as stj suggested. They won't be nearly as expensive as the two 4700 uF 25V units.

            Another thing worth mentioning is that, depending on the output voltage of the transformer, you may use a linear regulator to feed the amplifier. When you do that, this should eliminate pretty much all of the hum. Something like a 7812, 7815, or 317 (adjustable) should be fine, so long as you put a proper heatsink on it and don't exceed its specs. But this suggestion is perhaps more fitting if you like playing with amps an audio gear.
            +1 ..

            Better also change wires , they may be rusty after long use .

            Comment


              #7
              Re: Computer speakers - fixing hum

              I would start with the connector ..the switch get stuck in side grounding out.
              Techman1025

              Comment


                #8
                Re: Computer speakers - fixing hum

                Originally posted by jiroy View Post
                +1 ..

                Better also change wires , they may be rusty after long use .
                And that heatsink. Thats got to be more Oxide than Aluminium.... /s
                Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....

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                Comment


                  #9
                  Re: Computer speakers - fixing hum

                  Originally posted by eccerr0r View Post
                  curious if there's hum when no signal is presented?
                  Yes
                  better to keep quiet and be thought a fool, than to open your mouth and remove all doubt

                  Comment


                    #10
                    Re: Computer speakers - fixing hum

                    I would scope the DC supply lines and see if your introducing hum via poor smoothing of the DC supply.
                    Willing to help but I'm no expert.

                    Comment


                      #11
                      Re: Computer speakers - fixing hum

                      Originally posted by dick_barton View Post
                      would scope the DC supply lines
                      Not an option for me, neither scope nor knowledge how to use

                      Waiting on caps from China - I know, I know - but RS Components pissed me off with their MOQ for 1uf 63v, and delivery charges rule out other top tier vendors
                      better to keep quiet and be thought a fool, than to open your mouth and remove all doubt

                      Comment


                        #12
                        Re: Computer speakers - fixing hum

                        The 1 uf cap sounds like for coupling cap, may be you can use 2.2, or 4.7uf just for testing for now, but if they are coupling caps then I doubt that it will fix the hum problem. since the highest rate Voltage cap is 25V then it does not have to be rated at 63V.
                        Last edited by budm; 07-08-2017, 10:44 PM.
                        Never stop learning
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                        Inverter testing using old CFL:
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                        Comment


                          #13
                          Re: Computer speakers - fixing hum

                          I replaced all six caps with:
                          - 4700uf 25v - Nichicon PW
                          - 33uf 16v - Rubycon YK
                          - 1uf 63v - Panasonic EB

                          I reckon they're all genuine, otherwise pretty convincing fakes - and all tested OK on Banggood kit Transistor Tester

                          FWIW, both old 4700uf & one 33uf tested as "No, Unknown or Damaged"

                          All the old ones were marked 85 - but no way did I buy those speakers in 1985, more like 1995

                          And the outcome - no more hum and clear as a bell

                          My thanks to everyone who contributed
                          Attached Files
                          better to keep quiet and be thought a fool, than to open your mouth and remove all doubt

                          Comment


                            #14
                            Re: Computer speakers - fixing hum

                            Originally posted by pfrcom View Post
                            All the old ones were marked 85 - but no way did I buy those speakers in 1985, more like 1995
                            85 is the temperature rating in C.

                            Nice fix BTW.

                            Comment


                              #15
                              Re: Computer speakers - fixing hum

                              Originally posted by pfrcom View Post
                              All the old ones were marked 85 - but no way did I buy those speakers in 1985, more like 1995
                              Originally posted by diif View Post
                              85 is the temperature rating in C
                              Full disclosure:




                              I assumed 40/85 was a date, but maybe it's tolerance/temperature
                              Attached Files
                              better to keep quiet and be thought a fool, than to open your mouth and remove all doubt

                              Comment


                                #16
                                Re: Computer speakers - fixing hum

                                No it's temperature rating.
                                From -40°C to +85°C

                                CD11 is the datecode
                                "The one who says it cannot be done should never interrupt the one who is doing it."

                                Comment


                                  #17
                                  Re: Computer speakers - fixing hum

                                  Originally posted by pfrcom View Post
                                  FWIW, both old 4700uf & one 33uf tested as "No, Unknown or Damaged"
                                  Wow, even the 4700 uF units tested open?!?!

                                  Those are some seriously crappy caps then.

                                  Nice job on the fix. Those Nichicon PW caps should not give you any trouble for at least the next 15 years (I'd say at least 25, though).
                                  Last edited by momaka; 08-04-2017, 12:30 AM.

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