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Class AB or Class D for a home theater amplifier

  1. Dec 20, 2016 #1
    I am planing to assemble a 5.1 channel amplifier. I selected the famous TDA2030 as the basic element and is simple to proceed. But I have a confusion, whether to use some other Class D amplifier for better quality.Conceptually, a Class D amplifier is considered by some music purists to be less "perfect" in music rendition than a Class AB. This is because at the end of the day, a Class D amplifier generates digital pulses, which are then low-pass filtered to reconstruct the original sound.

    However, this distinction is perhaps more a preconception than human-discernible reality. Modern Class D amplifiers like the TPA3125D2 work at high enough oscillator frequencies (300 KHz) that the low-pass filter node frequency can be well above the ability of the human ear to perceive - 60 KHz or higher frequency low-pass filters have been used in DIY audio amplifier designs.

    Class AB too can suffer from distortion, especially if the load impedance is not well matched to the design, or the AB amplifier inherently has poor crossover distortion profiles. This is not so evident in "famous" Class AB chip amps such as the TDA2030 or the LM3886, both of which boast excellent Total Harmonic Distortion figures.

    Also, Class AB amplifiers can conceivably exhibit distortion at lower frequencies as well, where the human ear is more sensitive to such distortion. Class D distortion is significantly at the top end of the audio band, and beyond.

    A bigger cause for concern around audible distortion in DIY audio amplifiers is power-rail voltage droop under load. While the power supply could be designed to comfortably provide sufficient current to exceed the RMS power rating of the amplifier design, the actual power requirement rises to much more than a hypothetical Sqrt(2) x RMS wattage + overhead. Even 4 x rated RMS wattage might be momentarily breached in practice, such as during big drums and cymbals clashing at once.

    If the power supply tops out in those moments, and especially if the voltage regulator's protection circuitry takes time to recover, you have harsh distortion, more discernible than any amplifier chip choice would expose you to.

    Please share your experience about these classes of amplifiers in the term of their output quality. I really don't care about the efficiency or the size.
     
  2. jcsd
  3. Dec 20, 2016 #2
    One could argue endlessly about the differences in quality of various audio systems and people do. I think in the end it is pretty subjective. Are you the kind of person that thinks they can hear all that very subtle distortion? If you are then the listen to both and decide for yourself because no amount of data will convince you. If you are more scientific in your approach then I think the answers you seek are out there and the data and arguments far too voluminous to reiterate in a few lines here.
     
  4. Dec 20, 2016 #3

    jim hardy

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    If i've ever heard a class D i was unaware,
    surely my kids' modern 'earth-shaker ' home theaters are class D because heatsinks are conspicuously absent.

    I have a pretty good ear , and my opinion is:

    any difference in sound is due less from amplifier class A or D than from amplifier output impedance .


    Since you're experimenting why not build one that takes at least some of its feedback from speaker current instead of speaker voltage ?
    http://www.edn.com/design/consumer/...periority-of-current-drive-over-voltage-drive

    my two cents, and overpriced at that
     
  5. Dec 21, 2016 #4

    Averagesupernova

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    The active subwoofer on my home theater system seems to have a pretty small heatsink also considering what it has to do. It used to be you had main front speakers each with a pretty large woofer and one or two midranges and tweets. The industry has gone away from that to single subwoofers. Think about it. Running sub with class D is pretty easy. Rather trivial to filter out the switching frequency in the woofer and subwoofer range and this is where the most power is in music. So now the amplifiers have shrunk in size for the main front speakers due to lower power requirements and running class D for the low end is a snap.
     
  6. Dec 21, 2016 #5

    jim hardy

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    Indeed that's the approach i'd take today . Big linear low frequency amps are expensive to build if only for the heatsinks and requisite coupling capacitors . But mid and high are a snap with those TDA series IC linear amps.

    Motorola used the bi-amp approach in late fifties/early sixties. Bass isn't very directional . My family's hi-fi was a Motorola SK47 console..
    http://www.radiomuseum.org/r/motorola_sk47m_hs_816_hs_818.html?language_id=2

    It used two sets of push-pull 6BM8's( i think)maybe ten watts a side, driving 8" mid and 5" tweeters left and right, and a push-pull 6BQ5 stage maybe thirty watts to a 15 inch woofer in the center. Sound was fantastic for the time.
    sk47.jpg

    All powers were listed as peak instantaneous, probably 4X the true power.
    I duplicated the amplifier and took it with me to college in '64, just mounted speakers in a wood box. It was regarded best sounding system on the floor.

    Note that ten watts is plenty of sound for any reasonable in home listening. In an apartment it is enough noise to make the neighbors call the cops.
     
  7. Dec 21, 2016 #6

    Averagesupernova

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    10 Watts? Bah... How can I listen to my tunes while mowing the yard? :)
     
  8. Dec 22, 2016 #7

    Svein

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    Motorola used to have application notes with schematics for some very good amplifiers. Use Google and search for AN-485.
     
  9. Dec 22, 2016 #8

    jim hardy

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