8 ms·

Benefits of Class-G and Class-H Boost in Audio Amplifiers [pdf]

48 points by type0 4y ago

skybrian 4y ago
Interesting. Are there any products that use this? Development boards? I hope to build a musical instrument someday with an integrated speaker.
- klodolph 4y ago
  This has been around for years. Self's webpage [1] notes that class G amps date back to 1976. They've certainly been used in commercial applications and I'm certain you could buy PCB kits at some point in history. Apparently, there were a bunch of class G amps that appeared after 5.1 setups got popular, just because of how much less heat they produce per channel. If you want an efficient, small amplifier these days, class D is also an option. They're cheap, small, and powerful. Much more efficient than class G. If you are just trying to stick a speaker and amp in a musical instrument, I would start by getting an amp that is built into an IC with something that can work with a relatively simple power supply. [1]: http://www.douglas-self.com/ampins/classg/g.htm http://www.douglas-self.com/ampins/classg/g.htm
  - analog31 4y ago
    Among the things that have happened since 1976 are super high performance MOSFETs, that play directly into the hands of Class-D amplifiers. But actually making Class-D amps robust involves a steep learning curve and an expensive oscilloscope. This is the reason why, for example, musical instrument amplifiers tend to use pre-made Class-D amp modules such as those made by IcePower. The amplifier that I use for playing the bass is Class-D, as are all of the audio amplifiers feeding speakers in my house.
    - skybrian 4y ago
      Hmm. IcePower looks pricey and it's probably not for portable, battery-powered audio?
      - analog31 4y ago
        They're not for battery power, since a major part of their appeal is integration of the power supply and amplifier on a single board. Some of the other modules sold by Parts Express are designed for lower voltage DC power. Then it becomes a matter of how much power you need, for how long, and what that translates into in terms of battery capacity. Speaker efficiency also plays an obvious role.
  - aidenn0 4y ago
    When I've done my own designs, the output filter of the class D is rather sensitive to which speaker is used; it seems like class D is great when you are building an integrated product (HTIB (do those even exist anymore?). powered speaker, instrument amp &c.), but H would be better for separates.
Tsiklon 4y ago
I wonder why these haven’t become more well known among Audio folks, more power at higher efficiency is a good thing, if it comes with suitably appropriate low levels of undesirable distortion
- dsr_ 4y ago
  Almost all of the top-rated audio amplifiers use class-D switching already; the class G and H changes are only needed in battery-driven devices. E.g.: https://www.audiosciencereview.com/forum/index.php?threads/topping-la90-review-integrated-amplifier.33374/ https://www.audiosciencereview.com/forum/index.php?threads/t...
  - jeffbee 4y ago
    A lot of the stuff at the high end of the chart is using not only the same architecture, but the same modules from the same supplier. Interesting that the class-AB amp that has been at the top of their ratings for years has finally been beaten by a switching amp.
    - JohnBooty 4y ago
      Is the Benchmark AHB2 (the previous champ) really class AB? I think it's more like a switching (class D) amp. Those AHB2's are tiny and run cool while putting out a few hundred watts of power - I think that rules out class AB.
      - jeffbee 4y ago
        They’re small and cool because they have the “class-h” active rail system described in this app note. Someone else said that’s only for battery-powered mobile devices but that’s not true.
  - aidenn0 4y ago
    I thought it was the opposite; class-D is more likely in battery powered because it is higher efficiency than G or H, and G or H are used in high powered amplifiers that have an AB output stage but are thermally limited?
Severian 4y ago
If anyone wants to easily get into Class D amps, Parts Express has private label Dayton Audio amps [1] with a variety of features and wattage levels. They use Wondom/Sure as their supplier [2]. They are pretty feature rich: they support I2S, Bluetooth, and Sigma Studio for DSP effects (using the Analog Devices ADAU170 IC). I myself am pricing out a kit so I can build a ammo-can speaker box. I'll probably go with Parts Express as it's a 1.5hr drive to visit the brick and mortar store, and I can get the speaker drivers as well (plus other components). [1]: https://www.parts-express.com/electronic-parts/audio-amplifier-boards-modules https://www.parts-express.com/electronic-parts/audio-amplifi... [2]: https://store.sure-electronics.com/ https://store.sure-electronics.com/
- iancmceachern 4y ago
  I love parts express. They have the stuff to make yourself very high end speakers and a lot of very high quality amplifier and other electronics modules.
- flaviut 4y ago
  I'm not an expert on audio, but what's the difference between [1], and the reference design of [2]? I know only a bit about electronics, but I would have figured the market would have driven those two things to be roughly the same price if they were equivalent. [1]: https://www.parts-express.com/ICEpower-200ASC-Class-D-Audio-Amplifier-with-Power-Supply-Module-1-x-200W-326-208 https://www.parts-express.com/ICEpower-200ASC-Class-D-Audio-... [2]: https://www.ti.com/lit/ds/symlink/tpa3221.pdf?ts=1656082484819 https://www.ti.com/lit/ds/symlink/tpa3221.pdf?ts=16560824848...
  - deleted 4y ago
    [deleted]
  - digitallyfree 4y ago
    From what I know ICEpower chips are intended for (and used in) "high end" applications while the TI ones are intended for general purpose consumer devices. At least that's how they're marketed and an amplifier manufacturer will often state specifically that they use an ICEpower chip in their amp. Whether or not one can hear the difference is another story.
watersb 4y ago
Good times in the 2000s with the Tripath amplifier chips. Vinnie Rossi took them out of mass-market Technics surround sound boxes and created some really nice amplifiers. Then he rolled his own, using batteries to drive the amplifiers, independent of the AC mains electric supply. A 2007 deep dive at Six Moons warning very heavy audiophile reality https://6moons.com/audioreviews/redwine8/ https://6moons.com/audioreviews/redwine8/ I have a base model Signature amplifier and I really like it. Rossi followed up with improved models that replaced the sealed lead-acid batteries with LiPo, and then ditched the batteries altogether with a super-capacitor design. I can't find the old company, maybe it is no longer in business. But looks like Rossi has a web site still up at https://www.vinnierossi.com https://www.vinnierossi.com
aftbit 4y ago
Class H sounds a lot like envelope tracking in RF.
londons_explore 4y ago
This seems like only half way to the ideal solution... The ideal solution would be to use a DC-DC buck boost power supply to directly supply the speaker. Get rid of the intermediate power rail and ESR losses by effectively converting the power twice. Obviously you will need to do some work on the control algorithms, because rather than your power supply aiming for a nice stable output voltage, you're now aiming for a voltage waveform exactly matching the target signal. You also no longer care directly about ripple voltage, but do care about linearity and THD.
londons_explore 4y ago
It would be nice to do something about efficiency in the left half of the charts too. I understand that my Bluetooth speaker only lasts a few hours when cranked up to full volume. But when I have it on as quiet background music I'd really like it to last a week. Audio is perceptually logarithmic, so quiet sounds use very little energy to produce. That means that with carefully designed stuff we should be able to get really long battery lives.

48 points by type0 4y ago

Interesting. Are there any products that use this? Development boards? I hope to build a musical instrument someday with an integrated speaker.

klodolph 4y ago
This has been around for years. Self's webpage [1] notes that class G amps date back to 1976. They've certainly been used in commercial applications and I'm certain you could buy PCB kits at some point in history. Apparently, there were a bunch of class G amps that appeared after 5.1 setups got popular, just because of how much less heat they produce per channel. If you want an efficient, small amplifier these days, class D is also an option. They're cheap, small, and powerful. Much more efficient than class G. If you are just trying to stick a speaker and amp in a musical instrument, I would start by getting an amp that is built into an IC with something that can work with a relatively simple power supply. [1]: http://www.douglas-self.com/ampins/classg/g.htm http://www.douglas-self.com/ampins/classg/g.htm
- analog31 4y ago
  Among the things that have happened since 1976 are super high performance MOSFETs, that play directly into the hands of Class-D amplifiers. But actually making Class-D amps robust involves a steep learning curve and an expensive oscilloscope. This is the reason why, for example, musical instrument amplifiers tend to use pre-made Class-D amp modules such as those made by IcePower. The amplifier that I use for playing the bass is Class-D, as are all of the audio amplifiers feeding speakers in my house.
  - skybrian 4y ago
    Hmm. IcePower looks pricey and it's probably not for portable, battery-powered audio?
    - analog31 4y ago
      They're not for battery power, since a major part of their appeal is integration of the power supply and amplifier on a single board. Some of the other modules sold by Parts Express are designed for lower voltage DC power. Then it becomes a matter of how much power you need, for how long, and what that translates into in terms of battery capacity. Speaker efficiency also plays an obvious role.
- aidenn0 4y ago
  When I've done my own designs, the output filter of the class D is rather sensitive to which speaker is used; it seems like class D is great when you are building an integrated product (HTIB (do those even exist anymore?). powered speaker, instrument amp &c.), but H would be better for separates.

Tsiklon 4y ago

I wonder why these haven’t become more well known among Audio folks, more power at higher efficiency is a good thing, if it comes with suitably appropriate low levels of undesirable distortion

dsr_ 4y ago
Almost all of the top-rated audio amplifiers use class-D switching already; the class G and H changes are only needed in battery-driven devices. E.g.: https://www.audiosciencereview.com/forum/index.php?threads/topping-la90-review-integrated-amplifier.33374/ https://www.audiosciencereview.com/forum/index.php?threads/t...
- jeffbee 4y ago
  A lot of the stuff at the high end of the chart is using not only the same architecture, but the same modules from the same supplier. Interesting that the class-AB amp that has been at the top of their ratings for years has finally been beaten by a switching amp.
  - JohnBooty 4y ago
    Is the Benchmark AHB2 (the previous champ) really class AB? I think it's more like a switching (class D) amp. Those AHB2's are tiny and run cool while putting out a few hundred watts of power - I think that rules out class AB.
    - jeffbee 4y ago
      They’re small and cool because they have the “class-h” active rail system described in this app note. Someone else said that’s only for battery-powered mobile devices but that’s not true.
- aidenn0 4y ago
  I thought it was the opposite; class-D is more likely in battery powered because it is higher efficiency than G or H, and G or H are used in high powered amplifiers that have an AB output stage but are thermally limited?

Severian 4y ago

If anyone wants to easily get into Class D amps, Parts Express has private label Dayton Audio amps [1] with a variety of features and wattage levels. They use Wondom/Sure as their supplier [2]. They are pretty feature rich: they support I2S, Bluetooth, and Sigma Studio for DSP effects (using the Analog Devices ADAU170 IC). I myself am pricing out a kit so I can build a ammo-can speaker box. I'll probably go with Parts Express as it's a 1.5hr drive to visit the brick and mortar store, and I can get the speaker drivers as well (plus other components). [1]: https://www.parts-express.com/electronic-parts/audio-amplifier-boards-modules https://www.parts-express.com/electronic-parts/audio-amplifi... [2]: https://store.sure-electronics.com/ https://store.sure-electronics.com/

iancmceachern 4y ago
I love parts express. They have the stuff to make yourself very high end speakers and a lot of very high quality amplifier and other electronics modules.
flaviut 4y ago
I'm not an expert on audio, but what's the difference between [1], and the reference design of [2]? I know only a bit about electronics, but I would have figured the market would have driven those two things to be roughly the same price if they were equivalent. [1]: https://www.parts-express.com/ICEpower-200ASC-Class-D-Audio-Amplifier-with-Power-Supply-Module-1-x-200W-326-208 https://www.parts-express.com/ICEpower-200ASC-Class-D-Audio-... [2]: https://www.ti.com/lit/ds/symlink/tpa3221.pdf?ts=1656082484819 https://www.ti.com/lit/ds/symlink/tpa3221.pdf?ts=16560824848...
- deleted 4y ago
  [deleted]
- digitallyfree 4y ago
  From what I know ICEpower chips are intended for (and used in) "high end" applications while the TI ones are intended for general purpose consumer devices. At least that's how they're marketed and an amplifier manufacturer will often state specifically that they use an ICEpower chip in their amp. Whether or not one can hear the difference is another story.

watersb 4y ago

Good times in the 2000s with the Tripath amplifier chips. Vinnie Rossi took them out of mass-market Technics surround sound boxes and created some really nice amplifiers. Then he rolled his own, using batteries to drive the amplifiers, independent of the AC mains electric supply. A 2007 deep dive at Six Moons warning very heavy audiophile reality https://6moons.com/audioreviews/redwine8/ https://6moons.com/audioreviews/redwine8/ I have a base model Signature amplifier and I really like it. Rossi followed up with improved models that replaced the sealed lead-acid batteries with LiPo, and then ditched the batteries altogether with a super-capacitor design. I can't find the old company, maybe it is no longer in business. But looks like Rossi has a web site still up at https://www.vinnierossi.com https://www.vinnierossi.com

aftbit 4y ago

Class H sounds a lot like envelope tracking in RF.

londons_explore 4y ago

This seems like only half way to the ideal solution... The ideal solution would be to use a DC-DC buck boost power supply to directly supply the speaker. Get rid of the intermediate power rail and ESR losses by effectively converting the power twice. Obviously you will need to do some work on the control algorithms, because rather than your power supply aiming for a nice stable output voltage, you're now aiming for a voltage waveform exactly matching the target signal. You also no longer care directly about ripple voltage, but do care about linearity and THD.

londons_explore 4y ago

It would be nice to do something about efficiency in the left half of the charts too. I understand that my Bluetooth speaker only lasts a few hours when cranked up to full volume. But when I have it on as quiet background music I'd really like it to last a week. Audio is perceptually logarithmic, so quiet sounds use very little energy to produce. That means that with carefully designed stuff we should be able to get really long battery lives.