Bad caps in cheap computer speakers

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  • tom66
    EVs Rule
    • Apr 2011
    • 32560
    • UK

    #1

    Bad caps in cheap computer speakers

    Speakers were a gift from a friend so I can't complain .

    Noticed that on certain sounds I'd get a crackling - usually louder sounds.

    Fed it audio from Audacity at 440Hz and measured the output on my scope (with it driving the speakers)... sure enough it's got about 2Vp-p of 100Hz on it, and can also hear this weird "warbling" effect.

    So either it's bad caps or just insufficient from the start. Need to crack them open to upgrade the amplifier anyway, it clips at around 7Vp-p to the speakers...
    Last edited by tom66; 10-04-2012, 12:57 PM.
    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
    For service manual, schematic, boardview (board view), datasheet, cad - use our search.
  • gilly1984
    Badcaps Veteran
    • Jun 2012
    • 751
    • UK

    #2
    Re: Bad caps in cheap computer speakers

    Originally posted by tom66
    Speakers were a gift from a friend so I can't complain .

    Noticed that on certain sounds I'd get a crackling - usually louder sounds.

    Fed it audio from Audacity at 440Hz and measured the output on my scope (with it driving the speakers)... sure enough it's got about 2Vp-p of 100Hz on it, and can also hear this weird "warbling" effect.

    So either it's bad caps or just insufficient from the start. Need to crack them open to upgrade the amplifier anyway, it clips at around 7Vp-p to the speakers...
    I took a little circuit board out of a dab radio that feeds the aux out.

    Is it a little amp?

    Is has pins for l/r audio, gnd and 8volt dc.
    Do NOT touch heatsinks when testing for voltages as they may be LIVE!

    Comment

    • tom66
      EVs Rule
      • Apr 2011
      • 32560
      • UK

      #3
      Re: Bad caps in cheap computer speakers

      Probably not, maybe preamp.
      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

      Comment

      • gilly1984
        Badcaps Veteran
        • Jun 2012
        • 751
        • UK

        #4
        Re: Bad caps in cheap computer speakers

        Its a UTC4558 dual operational amplifier?

        Any good to make a headphone amp?
        Do NOT touch heatsinks when testing for voltages as they may be LIVE!

        Comment

        • mariushm
          Badcaps Legend
          • May 2011
          • 3799

          #5
          Re: Bad caps in cheap computer speakers

          Why don't you just use a TDA1308?

          Datasheet:

          Very simple to use and very cheap, you can find them for half a buck in lots of places.

          Comment

          • gilly1984
            Badcaps Veteran
            • Jun 2012
            • 751
            • UK

            #6
            Re: Bad caps in cheap computer speakers

            Originally posted by mariushm
            Why don't you just use a TDA1308?

            Datasheet:

            Very simple to use and very cheap, you can find them for half a buck in lots of places.
            I like messing with stuff i have around. Just trying to fine a use for it.

            Thanks though.
            Do NOT touch heatsinks when testing for voltages as they may be LIVE!

            Comment

            • Th3_uN1Qu3
              Believe in
              • Jul 2010
              • 6031
              • Romania

              #7
              Re: Bad caps in cheap computer speakers

              The 4558 does have enough grunt to drive headphones. You can use it. However, don't expect it to sound stellar, as they're pretty lousy opamps.
              Originally posted by PeteS in CA
              Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
              A working TV? How boring!

              Comment

              • gilly1984
                Badcaps Veteran
                • Jun 2012
                • 751
                • UK

                #8
                Re: Bad caps in cheap computer speakers

                Originally posted by Th3_uN1Qu3
                The 4558 does have enough grunt to drive headphones. You can use it. However, don't expect it to sound stellar, as they're pretty lousy opamps.
                Thanks.

                Not too bothered about quality, just as long as it is louder than my pc when ive had a few beers

                Can i leave it on the board its on?
                Do NOT touch heatsinks when testing for voltages as they may be LIVE!

                Comment

                • gilly1984
                  Badcaps Veteran
                  • Jun 2012
                  • 751
                  • UK

                  #9
                  Re: Bad caps in cheap computer speakers

                  Anyway, sorry for stealing your thread Tom.

                  Just got me thinking when you mentioned speakers.
                  Do NOT touch heatsinks when testing for voltages as they may be LIVE!

                  Comment

                  • tom66
                    EVs Rule
                    • Apr 2011
                    • 32560
                    • UK

                    #10
                    Re: Bad caps in cheap computer speakers

                    I'm trying to listen to human speech and it's just crackling on the peaks. Really distracting. Noticed the power LED goes out almost completely when sounds are louder.
                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                    Comment

                    • gilly1984
                      Badcaps Veteran
                      • Jun 2012
                      • 751
                      • UK

                      #11
                      Re: Bad caps in cheap computer speakers

                      Originally posted by tom66
                      I'm trying to listen to human speech and it's just crackling on the peaks. Really distracting. Noticed the power LED goes out almost completely when sounds are louder.
                      Stick a bigger cap on it.
                      Do NOT touch heatsinks when testing for voltages as they may be LIVE!

                      Comment

                      • tom66
                        EVs Rule
                        • Apr 2011
                        • 32560
                        • UK

                        #12
                        Re: Bad caps in cheap computer speakers

                        I will....
                        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                        Comment

                        • gilly1984
                          Badcaps Veteran
                          • Jun 2012
                          • 751
                          • UK

                          #13
                          Re: Bad caps in cheap computer speakers

                          Originally posted by tom66
                          I will....
                          Of course you will, why did i even say it lol.
                          Do NOT touch heatsinks when testing for voltages as they may be LIVE!

                          Comment

                          • ben7
                            Capaholic
                            • Jan 2011
                            • 4059
                            • USA

                            #14
                            Re: Bad caps in cheap computer speakers

                            Originally posted by tom66
                            I'm trying to listen to human speech and it's just crackling on the peaks. Really distracting. Noticed the power LED goes out almost completely when sounds are louder.
                            Could be lame transformer, or lame rectifiers too!

                            You can find lots of rare brands in computer speakers - once I found some 'Scatronics' brand capacitor!
                            Muh-soggy-knee

                            Comment

                            • JuniperSprouts
                              Solder Soldier
                              • Aug 2010
                              • 119

                              #15
                              Re: Bad caps in cheap computer speakers

                              You can find lots of rare brands in computer speakers - once I found some 'Scatronics' brand capacitor!
                              German?

                              Comment

                              • tom66
                                EVs Rule
                                • Apr 2011
                                • 32560
                                • UK

                                #16
                                Re: Bad caps in cheap computer speakers

                                Found the bulk cap to be a 470uF 16V... yeah, that's it. The transformer is the lossy part - but I'm going to work around this by sticking in a 6800uF 16V (possibly two in parallel.) The output coupling caps are just 220uF, and the input caps are 22uF with a 1kohm load resistor.

                                This sets the -3dB for the input at 7 Hz, and the output is 180 Hz. Can be better. The output caps will be upgraded to 6800uF 16V, and the input caps are going to 100uF. This'll give it a 12 Hz -3dB. Later, I'll conside upgrading it using a class-D type amplifier and consider modding it onto the 12V supply from my PC, as the transformer is just a 9V 200mA type, so pretty puny.

                                Vcc is normally 14V (with no audio) but drops as low as 4.5V during loud voice excursions.

                                Speakers aren't too shabby - if they're honest, they claim to be 4 ohm, 3W types. They look big enough to be about that. The amp IC though, it's just a D2822N; a stereo 1W amplifier.

                                Cap I'll use:
                                http://uk.farnell.com/panasonic/eca1...16v/dp/8767203
                                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                                Comment

                                • Th3_uN1Qu3
                                  Believe in
                                  • Jul 2010
                                  • 6031
                                  • Romania

                                  #17
                                  Re: Bad caps in cheap computer speakers

                                  Large output coupling caps isn't a good idea with small speakers and puny little chip amps - you'll be wasting power in frequencies the speakers cannot reproduce. 1000uF will be enough.
                                  Originally posted by PeteS in CA
                                  Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                                  A working TV? How boring!

                                  Comment

                                  • tom66
                                    EVs Rule
                                    • Apr 2011
                                    • 32560
                                    • UK

                                    #18
                                    Re: Bad caps in cheap computer speakers

                                    Hmm, need to check what the minimum frequency the speakers can do. Can't think of a way to do this without a signal generator, and I only have access to one at the uni labs. Time to grovel .
                                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                                    Comment

                                    • Th3_uN1Qu3
                                      Believe in
                                      • Jul 2010
                                      • 6031
                                      • Romania

                                      #19
                                      Re: Bad caps in cheap computer speakers

                                      Use Sony Sound Forge, TrueRTA, Audacity or Visual Analyzer and there you got your signal generator.
                                      Originally posted by PeteS in CA
                                      Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                                      A working TV? How boring!

                                      Comment

                                      • mariushm
                                        Badcaps Legend
                                        • May 2011
                                        • 3799

                                        #20
                                        Re: Bad caps in cheap computer speakers

                                        tom66, do you really need 2 x 6800uF? Sincerely doubt you would actually need that much capacity, especially since it's a 1 watt-er.

                                        You should have some 3300uF / 16v caps in your boxes, I'd say just grab a couple of those and that should be enough.

                                        Comment

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