Class-D-elightful

Whether you fall into the “all well-designed amps sound the same when used within their limits” camp or the “amp selection is critical” army of true believers, it’s arguable that prior to the turn of the millennium amps designed for high-performance audio had fallen into a rut.

- By Thomas J. Norton

They were so good that the advertising for them had to become increasingly creative. But a parade of skilled designers remained convinced that the new concepts they had come up with were superior, and audiophiles still lined up to buy them. The turf was always familiar: tubes remained tubes with their lovable quirkiness, and solid-state was dominated by class-A/B designs as it had been since the transistor was invented.

Meanwhile, the digital era gathered steam, although digital implementations were slow to crash the well-entrenched amp party. An early design from Bang & Olufsen called ICEpower was dubbed class-D for obvious reasons.

There were undeniable benefits to class-D, particularly its high efficiency: While class-A/B designs are lucky to achieve around 60 percent efficiency with the remaining energy simply turned into heat, a class-D amp can reach above 90 percent.

A few years after birth of class-D, a young engineer at Philips in Belgium, Bruno Putzeys, designed his own version of a digital amp. He called it UcD for “Universal class-D.” A range of variations followed as Putzeys moved on from Philips to Hypex, where the latter marketed (and still does) products based on his designs.