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LM4780 Chipamp Redux

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  • LM4780 Chipamp Redux

    Hi All,

    I built my first LM4780 7 years when I got into this hobby. I rarely used it due to the very mediocre layout, the bad solder job, and pop and hum that accompany each power up. I've always like the sound, power output and the ability to handle low speaker impedance loads of the 4780, so I decided to chuck the old amp, and redo everything from scratch. My goal was to build a simple, inexpensive chipamp that sounds good, has ample power to handle my listening style (loud, lots of dynamics), and can handle all my 4-ohm speakers.

    - The PCB is on eBay and from HIFIDIY.NET. All components are sourced from Digikey, caps are "Audio" types, resistors are 1% metal film. As you can see, component count is very low. The LM4780 amp chips and LM7812 (voltage regulator) are free samples from TI.

    - The transformer is the Avel 330VA 25-0-25.

    - The power supply consists of a 25A/400V bridge rectifier (overkill, but I had it laying around), and Nichicon 10,000uF/50V ($3) from Apex Jr., and other components to mitigate noise from the transformer and the diode bridge.

    - Soft start module was built from a TI schematic.

    - Speaker protection is from an eBay kit, powered by a 12VAC/1A transformer, which output is also rectified to provide DC for the LED and fan.

    - The LM4780 boards are in a parallel configuration. These boards lack the optional zobel networks, so I added the 0.1uF caps and 2.7 ohm resistors between the output and the ground. The speaker outputs are then bridged with 0.1 ohm/3W resistors. The zobels are absolutely necessary to prevent oscillation and subsequent shutdown.

    This time, I think I achieved my goal of building a super quiet amp without pop, hum or buzz in a very compact Par-Metal case. Bass is very good, and detail excellent. There is a difference of about 5 to 6 degrees F between the heat sink channels, so apparently the gain is not equal. In the coming days, I will probably replace the gain resistors with better tolerance ones (0.1%).

    Thanks for reading.

    Hong
    Attached Files
    Some people are addicted to Vicodin. I'm addicted to speaker building.

    The Chorales - Usher 8945A/Vifa XT25TG Build
    ESP Project 101 Lateral MOSFET Amplifier
    LM4780 Parallel Chipamp
    Sonata Soundbar Project
    The Renditions - Active/Passive Towers

  • #2
    Re: LM4780 Chipamp Redux

    The PSU build.
    Attached Files
    Some people are addicted to Vicodin. I'm addicted to speaker building.

    The Chorales - Usher 8945A/Vifa XT25TG Build
    ESP Project 101 Lateral MOSFET Amplifier
    LM4780 Parallel Chipamp
    Sonata Soundbar Project
    The Renditions - Active/Passive Towers

    Comment


    • #3
      Re: LM4780 Chipamp Redux

      Soft start, speaker protection, and DC supply.
      Attached Files
      Some people are addicted to Vicodin. I'm addicted to speaker building.

      The Chorales - Usher 8945A/Vifa XT25TG Build
      ESP Project 101 Lateral MOSFET Amplifier
      LM4780 Parallel Chipamp
      Sonata Soundbar Project
      The Renditions - Active/Passive Towers

      Comment


      • #4
        Re: LM4780 Chipamp Redux

        Zobel and output resistors.
        Attached Files
        Some people are addicted to Vicodin. I'm addicted to speaker building.

        The Chorales - Usher 8945A/Vifa XT25TG Build
        ESP Project 101 Lateral MOSFET Amplifier
        LM4780 Parallel Chipamp
        Sonata Soundbar Project
        The Renditions - Active/Passive Towers

        Comment


        • #5
          Re: LM4780 Chipamp Redux

          Hong: That is a great job laying out all of your components,it would be hard to improve anything...Superb

          You should check your gain tracking by applying a sine wave to both channels simultaneously and use a scope probe on each channels output,then compare levels by moving trace A over trace B using the vertical position control.Use a dummy load for this.

          A temperature difference can also be attributed to how well the device is coupled to the heatsink,you should not use too much heatsink compound,just a thin coat will do.I noticed in one photo that one of the plastic screws is slightly cocked.You might want to use a wide metal washer under the plastic screws to distribute the clamping pressure across the device.

          Again...You are the Man ;)


          Here is a picture of a heat spreader on a chipamp from a car amplifier,this really distributes the clamping force to the heatsink.
          Click image for larger version

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          NLA

          Comment


          • #6
            Re: LM4780 Chipamp Redux

            I'll post the results after the scope job. Always learn good stuff from you. Do they sell these heat spreaders somewhere? I guess I can cut them out of metal. Thanks Bob.
            Some people are addicted to Vicodin. I'm addicted to speaker building.

            The Chorales - Usher 8945A/Vifa XT25TG Build
            ESP Project 101 Lateral MOSFET Amplifier
            LM4780 Parallel Chipamp
            Sonata Soundbar Project
            The Renditions - Active/Passive Towers

            Comment


            • #7
              Re: LM4780 Chipamp Redux

              Hong: One more point to make,there is no guarantee that each channel will be delivering the same amount of power to each channel at any given point in time,it depends on the left/right balance of the mix.The cumulative power delivered by the amp over time may be higher in one channel,thereby increasing the temperature of one channel versus the other.

              BoB
              NLA

              Comment


              • #8
                Re: LM4780 Chipamp Redux

                Hong: Here is a link to one of the vendors over at DIY audio his user name is Jackinnj,I have bought a lot of his pc boards for the LM4780 (bridged mode).I will be using them for a big project this fall. He uses a tensioning bar and is described in the link below,lots of good info for you on this page.

                link:
                http://tech-diy.com/LM4780_bridgedamp.htm
                NLA

                Comment


                • #9
                  Re: LM4780 Chipamp Redux

                  Bob,

                  I don't have a splitter that feeds the wave form into both channels, so I did it one channel at a time. Looks like there's a 5V difference between the left and right channel. Am I correct? Thanks.
                  Attached Files
                  Some people are addicted to Vicodin. I'm addicted to speaker building.

                  The Chorales - Usher 8945A/Vifa XT25TG Build
                  ESP Project 101 Lateral MOSFET Amplifier
                  LM4780 Parallel Chipamp
                  Sonata Soundbar Project
                  The Renditions - Active/Passive Towers

                  Comment


                  • #10
                    Re: LM4780 Chipamp Redux

                    Looks very good Hong. As Bob said, nice layout. Those heat sinks are huge. Do they need to be or was that just your choice?
                    " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                    Quote Originally Posted by hongrn. Oct 2014
                    Do you realize that being an American is like winning the biggest jackpot ever??

                    http://www.midwestaudioclub.com/spot...owell-simpson/
                    http://s413.photobucket.com/albums/pp216/arlis/

                    Comment


                    • #11
                      Re: LM4780 Chipamp Redux

                      Hong: Just use a jumper wire or an alligator clip to connect the two channels together.
                      NLA

                      Comment


                      • #12
                        Re: LM4780 Chipamp Redux

                        Very clean layout. Glad you worked out all the kinks from the first build.
                        I couldn't really tell - do you have a star ground between all the components?

                        I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                        "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                        High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                        SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                        My Voxel min sub Yet-another-Voxel-build

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                        • #13
                          Re: LM4780 Chipamp Redux

                          looks like you are running at full power, lower the generator level for about a ten volt rms reading and leave it that setting, we don't want to activate the protection circuits.Let it cool down and rerun for five minutes and then take your readings, do both channels at the same time.

                          I should have been more specific,my bad.
                          NLA

                          Comment


                          • #14
                            Re: LM4780 Chipamp Redux

                            One channel looks like 30 volts rms and the other channel at 27.9 volts rms.
                            A little hard to see the numbers that clearly on my end..

                            Use the Cyc rms number on the right of the scope...
                            NLA

                            Comment


                            • #15
                              Re: LM4780 Chipamp Redux

                              Looks great Hong! Really nice attention to detail.

                              Just curious, what are your scope images from? Are those exported from a DSO? Or is it a PC based measurement? I only have a Hitachi dual channel 35 MHz analog scope from the early 80's.
                              Expensive caps need time to break in. More expensive caps take a long time. Cheap caps sound great right out of the box.

                              Why I don't spray in first gear: http://s1138.photobucket.com/albums/...t=100_2585.mp4

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