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TPA3118 based 2.1 amp

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  • TPA3118 based 2.1 amp

    No links per house rules, but just received one of these from eBay for $13. This is the almost amp I've been waiting for.

    The sub volume sets the sub level and then the main volume controls the overall volume, as it should be. It seems dumb that I'd have to describe that, but most of these chinese 2.1 amps have independent sub and main controls, so you have to turn them both up to keep their relative levels the same, which is wildly inappropriate. The third knob is the crossover frequency control.

    The sound quality, while not quite up to the SMSL SA-36A Pro level (which used the same chip) is very good for this price. Power is adequate for some pretty serious listening and this thing is TINY. I'm running it with a 24V 5A power supply. The cons are:

    - No highpass for main speakers
    - only input is RCA and is right next to the 3 control knobs
    - I think the sub gain does not extend beyond the main gain, so the sub will need to be more efficient than the mains to have actual level matching control
    - Frequency sweep is weird. Reducing the xo frequency seems to reduce the level of the sub altogether. There is a usable range, but it's hard to dial in.

    This is close to the perfect 2.1 amp. What I really want is the MCA2250e in a tiny desktop format with some of the newer, great sounding chips. That plate amp has everything you need for a well adjusted 2.1 system. For $13, this eBay amp is a big step in the right direction.

    Dan
    _____________________________
    Tall Boys
    NRNP Computer Sub
    The Boxers
    The Hurricanes
    The Baronettes
    Conneccentric
    UX3

  • #2
    Originally posted by DanP View Post
    No links per house rules, but just received one of these from eBay for $13. This is the almost amp I've been waiting for.Dan
    So post a pic ...

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    • #3
      Easy enough to find, and remember, "If the power supply current is not sufficient, in the open large volume of dynamic will appear serious distortion and the phenomenon of sound".

      Comment


      • #4
        Originally posted by DanP View Post
        The cons are:

        - No highpass for main speakers
        - only input is RCA and is right next to the 3 control knobs
        - I think the sub gain does not extend beyond the main gain, so the sub will need to be more efficient than the mains to have actual level matching control
        - Frequency sweep is weird. Reducing the xo frequency seems to reduce the level of the sub altogether. There is a usable range, but it's hard to dial in.
        Dan
        I got the pic from eBay, not very high resolution. If you can take a high res pic or even a macro of the sub freq. pot and the nearby op amp(s), there's a good chance I could reverse engineer the circuit as the board is mostly single sided. You might be able to add some gain and resolve the freq vis-s-vis gain issue with a little bit of "surgery".

        And reducing the size of the L-R decoupling caps heading into the TPA3118 can provide a 1st order HP filter as the chip's input impedance is know (depends on the chip's gain setting).
        Last edited by Millstonemike; 12-04-2016, 02:58 PM. Reason: L-R decoupling caps..

        Comment


        • #5
          Originally posted by Millstonemike View Post

          I got the pic from eBay, not very high resolution. If you can take a high res pic or even a macro of the sub freq. pot and the nearby op amp(s), there's a good chance I could reverse engineer the circuit as the board is mostly single sided. You might be able to add some gain and resolve the freq vis-s-vis gain issue with a little bit of "surgery".

          And reducing the size of the L-R decoupling caps heading into the TPA3118 can provide a 1st order HP filter as the chip's input impedance is know (depends on the chip's gain setting).
          Man, all that sounds great, but how do you physically make modifications with these tiny components?! Here are some pics:

          Dan
          _____________________________
          Tall Boys
          NRNP Computer Sub
          The Boxers
          The Hurricanes
          The Baronettes
          Conneccentric
          UX3

          Comment


          • #6
            Originally posted by DanP View Post

            Man, all that sounds great, but how do you physically make modifications with these tiny components?! Here are some pics:

            Dan
            On a wing and a pray ...

            Photos still not good enough. I'll order one of these boards tonight. It could be several weeks before I get it. Patience is a virtue.

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            • #7
              Copying the Chinese, what a concept.

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              • #8
                Originally posted by Millstonemike View Post
                On a wing and a pray ...

                Photos still not good enough. I'll order one of these boards tonight. It could be several weeks before I get it. Patience is a virtue.
                Cool. I'm anxious to hear what you think is happening with the frequency sweep as well.

                Dan
                _____________________________
                Tall Boys
                NRNP Computer Sub
                The Boxers
                The Hurricanes
                The Baronettes
                Conneccentric
                UX3

                Comment


                • #9
                  Trevor Marshall (http://www.trevormarshall.com/class-d-tutorial/) has a very good tutorial on how to improve class D amps by replacing the input caps. It does require removing SMD caps, so solderer beware. I'd need a magnifier for my eyes and a couple of beers to steady my hands.
                  "Everything is nothing without a high sound quality." (Sure Electronics)

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