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Amplifier designers most certainly are. Class D has significant energy efficiency advantages, and significant sonic challenges. It’s taking an analog waveform,

Amplifier designers most certainly are. Class D has significant energy efficiency advantages, and significant sonic challenges. It’s taking an analog waveform, whether decoded by a DAC or starting as pure analog, and chopping it into a series of pulses (pulse width modulation). The amp is switching transistors on and off very quickly, rather than using them as a variable linear gain stage. It’s not the same as PCM encoded digital audio, and shouldn’t be confused with it.

foobarian 8y ago
The energy efficiency advantages in class D are incredible. When my old Technics receiver stopped working because it started overheating, i replaced it with a class D amp on a half-credit card sized circuit board from dx.com and taped it to the back of the TV. 20W per channel, which is plenty for my casual TV watching. The Technics was the size of several stacked pizza boxes, with fans and heat sinks etc.
sjwright 8y ago
> Amplifier designers most certainly are. Amplifier designers have to sell to a market that is rife with misinformation and a very poor signal-to-noise ratio between technical quality, profit margins and overall market success. I wouldn't expect many of them—especially the ones who have any name recognition—to be concerning themselves with objective technical performance. Whereas the guy who designed the amplifier circuits for a product where the customer isn't being placeboed by the spec sheet—like powered studio monitors, or consumer devices like the Apple HomePod—is far more likely to be focusing on objective measurement rather than faulty market perceptions.
AnthonBerg 8y ago
The thing is that transistors’ behvior is more linear and controlled when fully on or off rather than when used as continuously variable. Class-D can and does sound _amazing_ if built with good theoretical understanding. Check out Hypex amps designed by Dutch engineer Bruno Putzeys on strong control theoretical foundations.
- ballooney 8y ago
  That’s precisely and exactly the opposite of what ‘linear’ means when talking about the operating point of transistors. I think you should rephrase your argument.
  - AnthonBerg 8y ago
    I'm going with an understanding similar to what is presented e.g. here: https://www.mwrf.com/components/learn-meaning-amplifier-linearity https://www.mwrf.com/components/learn-meaning-amplifier-line... "The term linearity derives from an amplifier's linear relationship of input power to output power which, in an ideal amplifier, would be precisely related by the gain of the amplifier." I see it as matching my argument. Could I ask you to give a definition which clashes? Thanks!
    - ballooney 8y ago
      Yes, the definition of linearity is that f(A) + f(B) = f(A+B), which you have contradicted in your GP post. If a transistor is fully on, then doubling the input voltage to it will not double the output, because it's already at maximum. That is very precisely not a linear device. That's why linear amplifiers, like Class A, operate the transistor in a partially switched state, where increasing the input signal (about some bias point, and with feedback to turn a real transistor into a more ideally-behaving one) gives a corresponding increase in output signal. Class D (switching) amplifiers are _not_ linear, they trade linearity for efficiency. The article you linked to actually says this: "Over the years, a number of different biasing schemes have been developed for amplifiers, from extremely linear Class A operation, in which the active devices essentially remain powered on through the full sinewave cycle of an input signal, to more power-efficient schemes, such as Class D, in which multiple transistors are switched on and off to conduct different portions of an input waveform." I think what you are doing is confusing the linearity of the transistor with the linearity of the whole audio amplifier treated as a black box, which is why I suggested you rephrase your argument rather than say you are categorically wrong, however what you said was: "The thing is that transistors’ behavior is more linear and controlled when fully on or off rather than when used as continuously variable." ... which I'm afraid is really just wrong.

foobarian 8y ago

The energy efficiency advantages in class D are incredible. When my old Technics receiver stopped working because it started overheating, i replaced it with a class D amp on a half-credit card sized circuit board from dx.com and taped it to the back of the TV. 20W per channel, which is plenty for my casual TV watching. The Technics was the size of several stacked pizza boxes, with fans and heat sinks etc.

sjwright 8y ago

> Amplifier designers most certainly are. Amplifier designers have to sell to a market that is rife with misinformation and a very poor signal-to-noise ratio between technical quality, profit margins and overall market success. I wouldn't expect many of them—especially the ones who have any name recognition—to be concerning themselves with objective technical performance. Whereas the guy who designed the amplifier circuits for a product where the customer isn't being placeboed by the spec sheet—like powered studio monitors, or consumer devices like the Apple HomePod—is far more likely to be focusing on objective measurement rather than faulty market perceptions.

AnthonBerg 8y ago

The thing is that transistors’ behvior is more linear and controlled when fully on or off rather than when used as continuously variable. Class-D can and does sound _amazing_ if built with good theoretical understanding. Check out Hypex amps designed by Dutch engineer Bruno Putzeys on strong control theoretical foundations.

ballooney 8y ago
That’s precisely and exactly the opposite of what ‘linear’ means when talking about the operating point of transistors. I think you should rephrase your argument.
- AnthonBerg 8y ago
  I'm going with an understanding similar to what is presented e.g. here: https://www.mwrf.com/components/learn-meaning-amplifier-linearity https://www.mwrf.com/components/learn-meaning-amplifier-line... "The term linearity derives from an amplifier's linear relationship of input power to output power which, in an ideal amplifier, would be precisely related by the gain of the amplifier." I see it as matching my argument. Could I ask you to give a definition which clashes? Thanks!
  - ballooney 8y ago
    Yes, the definition of linearity is that f(A) + f(B) = f(A+B), which you have contradicted in your GP post. If a transistor is fully on, then doubling the input voltage to it will not double the output, because it's already at maximum. That is very precisely not a linear device. That's why linear amplifiers, like Class A, operate the transistor in a partially switched state, where increasing the input signal (about some bias point, and with feedback to turn a real transistor into a more ideally-behaving one) gives a corresponding increase in output signal. Class D (switching) amplifiers are _not_ linear, they trade linearity for efficiency. The article you linked to actually says this: "Over the years, a number of different biasing schemes have been developed for amplifiers, from extremely linear Class A operation, in which the active devices essentially remain powered on through the full sinewave cycle of an input signal, to more power-efficient schemes, such as Class D, in which multiple transistors are switched on and off to conduct different portions of an input waveform." I think what you are doing is confusing the linearity of the transistor with the linearity of the whole audio amplifier treated as a black box, which is why I suggested you rephrase your argument rather than say you are categorically wrong, however what you said was: "The thing is that transistors’ behavior is more linear and controlled when fully on or off rather than when used as continuously variable." ... which I'm afraid is really just wrong.