Harley: Where are we on the learning curve with this technology?
Putzeys: Pretty much all over the place. Class D amplifiers that are now on the market run the gamut from really primitive and intuitive designs all the way to boxes that are indistinguishable from good linear amplifiers with only the presence of a small 400kHz (carrier) residual to tell the difference. Everybody is on a different stage on the learning curve. On the mature end you have amplifiers that behave really well on the test bench, don’t color the sound, and don’t disturb radio reception. On the immature end you find flawed concepts like digitally controlled switchers that don’t even have a flat frequency response and that kill any radio in the building. So there isn’t really something like “the state of the art of Class D,” precisely because everybody is at very different stages in the evolution of the technology.
Harley: Jeff, what’s your view on that subject? Do you see large improvements
coming down?
Rowland: Yes, I concur with Bruno. I haven’t pitched my tent anywhere along the line of the evolution of this technology, because as we speak there is more development to come, but all new technology has to have a beginning point, and you carry it through its natural evolution. Yes there is, as Bruno says, a wide variation in the intuitive simple designs and the more mature designs. I won’t say it’s a mature technology, but from our experience we have seen it deliver on its promise. There are a lot of improvements coming. Switching technology definitely will progress, but the results that we have gotten in the last four years have been quite amazing.
Harley: Will switching amplifiers one day dominate the high-end market?
Rowland: I don’t think they will dominate so much as become an option, in the same way that solid-state hasn’t dominated vacuum tubes. The nature of high-end audio is that everybody has his own favorite technology, and customers have their own likes and dislikes and prejudices, and that’s the beauty of it. We all have our own pride and prejudice, and that will always exist.
Putzeys: Jeff pretty much nails the situation there. Class D is a technology that not everybody can easily launch into, which means that for Class D to become a very significant part of the high-end market, quite a number of companies would have to be doing what Jeff did—go to third parties and actually buy knowledge. Yet, the high-end market is a place where few companies are willing to be seen doing anything less than rolling their own circuits from scratch. That alone would account for the fact that many non-Class D products will remain on the audiophile market.
Also, and again very importantly, I myself am completely agnostic about how one achieves the results, and I simply reject the notion that any technology should be inherently superior, in sonic terms at least, to the other. For me it’s been a running joke to make a Class D amplifier that beat my previous linear design, and then when I’ve done that I go back to linear design and I’ll make a new one that beats my best Class D amplifier, and I keep going back and forth like that just for the heck of it. That’s never going to stop. If in, say, five years, you take the very best Class D amp and you take the very best linear amp and you set one against the other in a listening shoot-out, there will be no clear winner.
Someone who’s really good at designing linear amplifiers but who doesn’t feel up to the task of designing a switching amplifier should by all means stick to his guns
D’Agostino: I haven’t ever conducted a comparison in which I couldn’t determine a clear winner. It’s never been my experience to listen to any switching amplifier and walk away saying, “Yeah, that sounds right, that sounds like music.” And I’ve listened to them all, at least those that are commercially available. From my perspective I haven’t yet heard any switching amplifier that remotely resembles what a good linear amplifier does, but, on the other hand, people interpret sound in different ways
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