How do Class D amps make power?

June 28, 2022
 by Paul McGowan

11 comments on “How do Class D amps make power?”

  1. wow!!! I am the first person posting? Most of the time I will see FR first to get the ball rolling. Interesting and a bit baffling at the same time for my brain I will have to watch this a few times to understand the theory of square waves and why they are more efficient. Years ago there were very few class D amplifiers. I distinctly remember a marketing ploy from Pioneer Pulse Width Modulation in the 80’s regarding power supplies in amplifiers and the term non-switching amplifier. I have switched to all Class D amplifiers for my last car stereo install. It is important in automotive to get the most “bang” for your buck. Since huge cables running around in vehicles and large amps may need heavy duty alternators ect. I am able to get by with my HD alternator (160amps) vs 145 amp (stock) and 3 separate amplifiers and an 18″ sub with no electrical issues except perhaps some headlight blinking at night. I plan to switch to L.E.D. headlamps If I can find suitable replacements in the future. Class A/B amps would force one to use expensive aftermarket alternators rating in the hundreds of amps. In automotive installs since there is so much more residual noise vs a home system efficiency is most important to me such as ported subs ect. As always audio is a compromise.

    1. FR frequently being first to post has a simple explanation. Being close to the International Date Line, he gets Paul’s post many hours before others less geographically privileged.

        1. Hi Jim,
          More so on ‘Paul’s Posts’ (as it gets posted daily here in Sydney Australia
          bang on 6pm) than here on ‘Ask Paul’.
          Interestingly I bought an Onkyo – ‘A9755’ back in 2005 & it had dual big,
          heavy transformers in it, which is strange for a ‘D’ class.
          It really brought my vintage Celestion – ‘Ditton 66’ floorstanders to life.
          I had it for 14 years & sold it for AU$200 less than what I bought it for.
          So there was at least one other person in Australia who knew what an
          absolute gem of an amplifier it is.
          Cheers,
          Martin

          1. Hello Martin
            When I hear Australia I think of Men at work and Vegemite which I have never had. I am sure there are many more attractions and other interesting things that I do not know about. Greetings.

            Dual transformers could mean “Dual Mono”. I am a huge fan of Dual mono amps like Adcom and Bryston. I did read good things about your Onkyo amplifier but never owned one. I used to dream about that vintage all black Onkyo amp with the huge meters on it but could never afford it (I forget the model number). I still believe many many people want Vacuum tubes in the circuitry. Hybrids are a good example. Audio Research has hybrid preamps and Paragon has added some tiny tubes to some of their amplifiers. Interesting technology. Looks like class A/B will be here for a while but D may close the gap in the future. Perhaps Bob Carver can develop some trick circuitry to make the Class D equal to AB. He did something similar years ago and perhaps can do it again.

            1. Many attractions here Jim.
              We have the worlds most deadliest snakes, spiders & jellyfish
              …it’s a hoot!
              Vegemite is definitely an acquired taste; if you weren’t raised on the stuff then you most probably wont like it…that’s been the consensus so far.
              Yes, strange to have one big heavy-ish transformer in a ‘D’ class amplifier, let alone two, but there you go…it probably is a dual mono.
              I’m currently running another dual mono…a Musical Fidelity – ‘M6si500’…beast of a thing, 500wrms/ch/8ohms.
              I teach welding classes with it on the weekends 😉

              PS Audio & Jeff Rowland make some very nice ‘D’ class
              amps; but ultimately it’s up to your ears of course.

  2. Probably the most advanced Class D amps are made by NAD using the designs of the Class D “god” Bruno Putzeys. I have a Parasound 2350 which is similar to the backend of the PS Audio Stellar M7000. Both use ICE Power modules. I could have gone Class AB for my 600 watts per channel, but the heat and cost would have been prohibitive. I believe Class D is the future and you will be seeing more and more Class D as time goes on.

  3. I love the promise of Class D amps, and they do work, but for me they don’t cut it in home audio. I have tried several well regarded brands of Class D amps, but I (almost) always found that a good class AB amp sounds cleaner, more spacious, and more effortless, even compared to class D amps of a MUCH higher power rating. I do use them in my car audio installs, as I have a couple of vintage cars with puny alternators where that efficiency is essential. I still don’t think they sound as good as some of my old class AB car amps, but they were a heck of a lot cheaper.
    I may also be a little spoiled, as I have two Magnepan systems at home, one ARC driven, one C-J. Of course, my digitals are all run through PS Audio DAC’s. 🙂 Thanks for the always enlightening videos Paul. Cheers!

    1. Good afternoon ProfGrif!
      Both you and Jim5337, have the right idea when it comes to power amps that are designed to be used in caars and trucks.
      But what I see around here in Lake City Florida, is a quite lot of kids riding around here with large subwoofers and large class AB amps driving them, at super high volumes.
      But after awhile, they end up with dead batteries.
      But the crazy thing that they don’t understand, is why that is happening to them.
      Those class AB car amps, draws an offel lot of currant.
      But not only do they kill the batteries, they also end up killing their aultinaters.
      Class D amps don’t require an offel lot of currant to crank up the volume.
      But again, the kids here don’t know that.

  4. Thanks Paul. That’s clarified a few gaps in my understanding of how class D works. I didn’t quite understand the difference between pulse WIDTH modulation and pulse DENSITY modulation and when you’ve previously said that class D doesn’t mean ‘digital’ operation. Please correct me if I’m wrong but is it that PDM uses a bunch of pulses of equal duration squeezed closer together to make the peak part of a wavy signal whereas PWM uses a long, continuous ‘pulse’ over the duration of the peak parts of the signal?

    1. Sort of. The PWM part uses variable width pulses. They vary from the very thin to the very wide depending on the signal amplitude. Wider pulses stay on longer, thinner pulses shorter periods. In PDM all pulses are the same width, just some are on (1) or off (0), If enough 1s happen in a group we get a higher signal level and fewer is the opposite.

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