Class-A amplifier design is stagnating—that’s what class-D pioneer Bruno Putzeys contended in my discussions with him here and here about class-D. To re-quote him:

“Class-D amplifiers will continue improving gradually, not because they have to catch up with class-A (that time is past)…”

“It’s not that difficult to build a respectable class-A amplifier using nothing but a few well-worn rules of thumb. The result was that while class-D crept steadily forward, class-A pretty much stagnated.”

He added: “This has caused a curious paradigm reversal; the question is no longer whether class-D is approaching the quality of class-A, but how many class-A amplifiers can really claim to be up there with the best of class-D? Make no mistake, the fundamental fact still holds: any given level of performance is much easier to achieve in class-A than in class-D. But designers of class-A amplifiers have, by and large, sat on their laurels. I could easily design a better class-A amplifier, but I see no one waiting for a better petrol engine.”

And then there was the issue of price: “Current top-end class-D modules are now so good that in any sound system, irrespective of cost, any other link in the chain is much weaker,” said Bruno. “Even if future modules get better, the improvements are minuscule when compared to the impact of, say, the speaker. That’s also true of great class-A amps like the Boulder 2150. But why bother if a class-D amplifier that’s a fraction of the price and size will do just as fine?”

Yes, a class-D amplifier is generally cheaper to make or buy than its class-A or class-A/B counterpart. But the audiophile pursuit has always been more about the constant search for better sound than about affordability, and class-A amplification is, arguably, the most revered amplification class of them all for its distortion-free purity of sound, a by-product of the topology’s output transistors always running at full power rather than switching on and off at more restrained power like those in a class-A/B or class-D design.

But was Bruno’s assertion true, that class-A had reached a prolonged period of stagnation where designers seemed to be mostly coasting on the same ol’ technology rather than coming up with new ideas to advance it and, accordingly, keep it relevant? And was this prevailing complacency in class-A design causing class-A’s standing among amplifier classes to become increasingly more tenuous next to those of class-D and class-AB designs?

Of course, as someone who’s got skin in the class-D game, Bruno could be accused of being partial in his remarks about to class-A, but it’s not like Bruno is acting coy here. Another thing that may be telling is that Bruno’s digs, in our interviews, were aimed at class-A, not class A/B. If anything, Bruno seemed to be throwing down the gauntlet at class-A’s feet, almost daring its designers to tell him he was wrong. He had made a bold, sweeping claim, which would surely be met with rebukes from class-A representatives taking a stand for their cause, right?

Crickets.

Hoping to stir up a dialogue about class-A’s place in the audio hobby, I sent an email to a few prominent class-A designers and manufacturers you likely know (if you own a class-A amp, it was likely made by them). It began with me introducing myself, then asking if, as a designer or manufacturer of class-A amplification, they would like to respond to Bruno’s comments, which I’d copied in my email.

I also asked if they’d like to shed light on where they believed class-A technology was headed.

Finally, I asked: “If you believe that class-A sounds better than class-D, could you explain in which ways?”

I expected a handful of eager replies from people wanting to set the record straight or extoll class-A’s virtues, as I did from the class-D contingent for my class-D articles. But again, crickets.

This is not to suggest that the class-A people I sent an email to didn’t respond because they’re hiding something or agree with Bruno. They certainly didn’t have to respond, and it could be that my emails ended up in junk folders. It’s just that the silence that followed my mailing left me with a nagging feeling that there was something being left unsaid.

The one sentence that Bruno told me that lingered longest in my mind was: “Any given level of performance is much easier to achieve in class-A than in class-D. But designers of class-A amplifiers have, by and large, sat on their laurels.”

If that’s true, that could be a concern for those rooting for class-A. As Bel Canto’s John Stronczer pointed out in my article Is Class-D Technology About As Good As It’ll Ever Get?: “Technology is never static or else it dies.”

Is class-A a has-been technology? All I know for sure is what I heard from class-A amplifier manufacturers after Bruno threw down the gauntlet: crickets.

I would love to hear from those manufacturers, who have chosen to work with class-A over the other classes for some reason, to help set the record straight and continue this discussion.

ADDENDUM:

A day before this article was scheduled to be published, I was delighted to receive a reply from one of the class-A designers I sent that first email to—Nelson Pass of Pass Labs and First Watt. I hope it’s a harbinger of others to come:

Hi Robert,

My longtime business partner Joe Sammut used to say, “It’s entertainment, not dialysis”.  The audio industry is full of diverse tastes, and building what we ourselves like, we find that a percentage of the audiophile population picks our equipment and lives happily with it.

I respect Bruno’s efforts at improving the technology of class-D—I explored it years earlier, and got a good commentary from (Stereophile founder) Gordon Holt, but in the end it did not appeal to me, so I continued pursuing simple class-A circuits.

I do have a picture for you though….

best, np

Header image courtesy of Eugene Zh.