The Hifi Trajectory Of Class D Amplifiers

Its been interesting to read this thread after several years.


In only 4 years since this thread was started we see that class D has improved quite a lot. This fact is a simple proof that the technology wasn't (and likely isn't now) mature. We developed and filed for a patent which addresses a major source of distortion in class D amps- 'dead time'.  Others in this field, such as Merrill Audio, have recognized this issue and have been addressing it with good success. In addition, Gallium Nitride (GaN) transistors have come along, furthering the technology quite a lot.


Now if small players like Merrill or ourselves can contribute to the sport, its a pretty good bet that it is still in the steep part of the innovation curve. I am quite interested to see what other developments are around the corner.

Class D has completely taken over the bottom end of the market. The amps in your cell phone are class D.

Class D has arrived insofar as its ability to challenge conventional solid state is concerned. I use a Crown class D amp for amplification of my keyboards in my band. It has two channels each of about 500 watts and it weighs 22 pounds. The amp I had before had half the power and weighed nearly twice as much. That can be a big deal when you have to lug heavy equipment around every time you play.

When it comes to challenging tube amps there is still a ways to go however. I like to relate the story of a show we did with a number of other bands a couple of years ago. Our bass player uses a 400-watt vacuum tube Peavey amp which we offered to backline (the term refers to the amp staying on stage so other players could use it, reducing the setup time that the band needed to go on stage). However one band had a bass player using a 500-watt class D amp made by Orange. He thought the Peavey would not be able to keep up with the sound that he needed. I told him there was no way a 500 watt class D amp could keep up with a 400 watt tube amp- he was quite shocked.

So we had him audition the Peavey- what he found was it made far more energy than he could get out of his Orange, so much in fact that he felt it might be too much to handle so he went with his Orange anyway as the bass from the Orange was less prodigious.

Just so you know, bass amps are far less likely to get overdriven than guitar amps are. IOW this was not just a matter of distortion due to overload or anything like that.

My experience with class D in high end audio is similar- and is why I made the comment to that bass player. I've not seen a lot of change in the years since, so I suspect that if class D is able to surpass a good tube amp, that day is still a ways down the road.

Yes, the semiconductor industry really doesn't want to make linear devices if they can help it. Switch mode devices are easier and more profitable.

Kijanki, in case you didn't know it, most decent bass guitar amps are built along hifi lines. They have to be in order to sound right. If you get a chance, look up a schematic of an amp called the Marshall Major and you will see what I am talking about.

I'm not sure why you even
brought up the case of 500W class D not being able to keep
up with 400W tube amp, since it is irrelevant to our
discussion and refers to particular design and the way power
was specified (only 6.7% difference in perceived loudness
between 400W and 500W). In addition, in last decades bass
amplification in larger venues got into PA system, making
raw power of the bass amp relevant only for small theaters.

A smaller theater was exactly were my example occurred. It was not the overall power that was the issue- it was that the Orange lacked the bass impact and the player had grown used to that. Not all bass amps are cheaply made BTW- in order to sound right the demands are exactly the same as in a good home audio power amplifier. **That** is why I brought it up.

I'm pretty sure we can find 500W tube amp that doesn't keep up with 400W class D bass amp,

Good luck with that. While I do think that day is coming, its still a long ways off and that amp simply does not exist yet. I've no intention of arguing back and forth about it- this is simply how it is.

Has Class D arrived? Sure. But do they beat tube amps? That's an entirely different question!

You really do not have to defend your business every time someone speaks about liking SS kit better than tube kit.

I may be going out on a limb here... but I would presume that you never sat down and gave a serious listen to the likes, of say, a Merrill Audio Veritas mono block amp. If you can ever get the opportunity to hear them,I think you will be picking your jaw up off the floor...

Your presumption is incorrect- believe it or not what is actually " defending my business" is actually done by auditioning products like these and then assessing the threat. If you think about you will see that no business in high end can really exist in a vacuum (if you will pardon the expression...). We assess a lot of technologies to try to understand how that might affect us in the future- I would think anyone in it for the long haul would do just that!

Further, its my opinion that you didn't read my posts all that carefully. No worries- but read this one, because it explains in greater depth what I am actually thinking.

First- Its not like we can't make class D amps; we've been looking into it for over 10 years.

But more to the point I've not seen Class D threatening conventional tube amps let alone ours (which are less conventional)- **so far**. What I **do** see (or hear, as the case may be) is that class D has effectively supplanted the traditional solid state design in all but the very best of the traditional designs (which might be a misnomer, as the best solid state amps I am thinking of are leading edge and really are not that traditional). Otherwise what it still boils down to is still just about the same old tube vs transistor argument which has been there all along, although the goal posts have moved about somewhat.

Those of you who are familiar with price performance curves will understand why this is so, and thus is likely to be so for quite some time. What the question really becomes is what part of the price performance curve (for more understanding, google 'technology S curve') class D is on right now.

Its my surmise that class D is nearing or at the top of the most vertical part of the curve. This suggests that the technology is reaching maturity. This is certainly what its advocates would like us to believe! If this is so, then what follows are incremental improvements.

FWIW, transformer-coupled tube amps are a very mature technology so improvements over the last few decades have been fairly slight.

Now if you have been following along, if my surmise is correct than this debate will be on-going possibly for decades. If my surmise is incorrect, then class D is a bit lower on its ascendancy of the technology S curve. IOW, breakthroughs are still possible, causing the technology to achieve much greater performance than is available right now.

So which is it? The answer is we don't know. But its been around for a while and its clear that class D is much much better now than it was even just 10 years ago.

So I am sticking to my position, which is not based on a personal bias or some need to 'defend my business' that it is possible for class D to surpass not only traditional solid state but also tubes, **but the latter day has yet to arrive**. But I'm not ruling that out as one can see from my prior posts.