Class-D amps - a different re view

I just posted. I don't go to the circles much. They aren't into mavericks there. Not that they are here either! :)

I have not been following this rambling thread very closely, but perhaps I should clear up some common misconceptions about making Class D amps:

1.) They are cheap to build, and
2.) They are easy to build, because all you have to do is put it in an expensive box.

Well, yes, that can be the case. Indeed, I am sure that there are outfits doing just that. But to say that everyone does that is a gross oversimplification.

Let me give you an example of something similar. I'll let the readers draw their own analogy and conclusion.

About 15 years ago, National Semiconductor came out with a line of parts that has come to be known as "chip amps". We looked into them, to see if they could lead to building a very affordable amp. One that would come close to high-end expectations, without the high-end price.

Well, they sounded good enough to merit consideration, but..............

How much could we knock the price of an amp down by using them?

Depends. Depends on how you want to go about it.

If it has to look nice, you need a decent enclosure. Not cheap. You would need a large power transformer, and decent filter caps. Not cheap, either. Still needs a heat sink, cut down from an extrusion, milled, and anodised. Ok, we can cut down on the size of the PCB somewhat, won't have to buy a boatload of discrete parts and output devices. But how much will that be less than the cost of buying the chip and making a PCB for it?

In reality, not much. You still need the same size power supply. Same amount of heat sink radiating area. After all, it is basically just like any other amp, only with most (if not all) the electronic guts inside one chip.

So, when you get down to it, it is not really all that much cheaper.

In fact, it can cost more.

"Huh? Did he say 'more'? That can't be."

Sure it can. Think about this:

Let's say through "research" that you find that it doesn't work as well as expected with only one chip. There is an awful lot heat to get rid of, and from a small source. Heat sink or not, it is probably going to get hotter than several discrete output devices. And it is all in one chip.

Well, heat is the enemy of ICs. So, you futz around, and through your "research" you find out that for several reasons that it sounds better if you run 4.......or 6........or 8.......in parallel for each channel. Wait......we are back to where we started from: same enclosure, same power transformer and filter caps, same heat sink, and now the same size PCB with the same number of parts. Only 8 ICs cost more than 2 outputs and a handful of discrete components.

Sure, you could cut every corner in the book, and make something inexpensive. Sure, there would be a market for it. Especially if you made a gazillion of them to get the price under $1K.

Or, you could end up with a novelty that cost as much as a traditional amp. Perception being reality for most, how many folks would buy a $3000 amp with a bunch of ICs in it, when you can buy the same thing that actually looks like a real amp for the same price from the same company?

Guess what: we never made any.

OK, fast forward to 2000 and something.........

You can buy a Class D amp module..........cheaply if you buy enough...........and start making amps with them.

But wait! You still need that fancy box. And probably same ol' power supply. Unless you want to go for "novel", and put a switcher in it. You need to market to a different crowd if you go that route.

So, what have you saved? Obviously, no heat sink. And probably not much of a PCB.

You could take those savings and use them for nice touches, like say..........EMI control..........or well, there are lots of tricks that an experienced designer can do at this point. (Sorry, no inside info gets divulged at this point, gang.)

Bottom line is this:

Class D modules are a tool that a designer can use. How they choose to use them is the difference between inexpensive and over-priced. Good sounding, or just good enough. Or something in between.

Yes, you can make an amp without a lot of bother and expense by using them. The opposite is also true.

Apart from all the technicality just like to add one line. I listened to guitar recording by Julian Bream with a Class T the TA 10.1. Music was dynamic and string tones rich. On one track to the very end I heard harmonics of a struck string magnitude of same order with tape hiss then the sound stage subsided to blackness, no hum, noise or rumble and I was using LP. Never beofore I heard in such clarity.

Hear hear, Ar_t you have spoke no truer words.

I would guess this guy has not heard Spec amps nor Mola Mola.