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Interesting. Are there any products that use this? Development boards?

I hope to build a musical instrument someday with an integrated speaker.

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

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.

Hmm. IcePower looks pricey and it's probably not for portable, battery-powered audio?

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.

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.

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