raspberry/fahrnet/de

Class D Audio Amplifier

This is the prototype project for building a class D audio amplifier based on Texas Instruments' TPA3122D2 chip. The design is heavily related to the evaluation board. This prototype can be built on a bread board PCB with about 50mm by 85mm dimension.

Content

  • System description
  • Circuit design and layout
  • Hardware used/ Bill of material
  • Datasheets of Components
  • Image footage
  • First impressions


  • System description

    The overall design of this prototype is based on the evaluation desing from
    Texas Instrumens (slou214a). I applied a littel interface adder to control the
    mute signal from any MCU voltage reference by adding a transistor logic.
    
    Components have been selected from an easily accessible supplier base and might
    slightly vary in performance characteristics. The output LC-filter inductor has
    been selected to almost match with the type given in the TI reference design -
    however quality reference source from W├╝rth Electronic could be sourced from
    Conrad Elektronik, a somewhat cheaper reference was chosen (see for BOM/
    datasheets).

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    Circuit design and layout

    Download the latest EAGLE files (schematic & layout): 
    
    article_d-ampvp1_schematic_layout.zip (zip-container)
    
    Alternatively, get the schematic as PDF:
    
    article_d-ampvp1_schematic.pdf

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    Hardware used/ Bill of material

    Download the latest BOM including referenced suppliers as csv-file: 
    
    article_d-ampvp1_bom.csv

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    Datasheets of Components

    The following list allows you to access datasheets to the components used -
    refer to the BOM for referenced resources:
    
    
  • electrolytic capacitor, 470uF
  • inductor, 22uH
  • class d audio amplifier chip, TPA3122D2
  • metalised polyester film capacitor, 680nF
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    Image footage

    The following image shows the readily assembled amp. The TI chip is not yet installed.
    
    
    
    

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    First impressions

    The first impression is rather impressive!
    
    Using my lab power supply at 15V and connecting my smart phone returns pretty 
    cool audio quality - considering some 10EUR in material, two old loudspeakers
    and some 2 hours of soldering and assembly.
    
    For an implementation solution I had intended to use a switch mode power supply (SMPS)
    from Meanwell. It turns out, that when not playing music the amp goes to some
    "hardly using any energy" mode (which surely is one of the reasons for going for a D-amp).
    Unfortunately, that leaves the SMPS with almost no load and as with many SMPS driven
    at low loads the SMPS started to make some audible noise itself - rather odd.
    
    Verdict: cheap and powerful audioamplifier with impressive audio output. The powering
    concepts needs to be carefully planned, however.
    
    The implementation project piNOS audio system gives some further insight 
    and more about audio capabilities.

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