October 2021

What Is Class D Amplification?
I've yet to be convinced that Class D sounds better.
Editorial By Noel Keywood

  If you want a powerful amplifier in a small case, a Class D NCore amplifier from Hypex (Netherlands) has become a popular choice" I said last month. Reason being NCore has overcome all the problems of Class D, notably high frequency distortion, load sensitivity and D.C. on the loudspeaker terminals.

So I was a bit taken aback to encounter all these problems on Technics new SU-R1000 Reference not-Class D amplifier you can read about on p10. I have to call it that at their insistence, but that it's not Class D is a technicality: all the same issues arise. It is what is commonly termed an 'analogue switching amplifier'. These have been around for 20 years or more, without gaining popularity – so a surprise that Technics should try again in unconvincing fashion.

Producing a 'digital amplifier' is an amusingly fruitless goal. No one can agree on what such a thing is in the first place, and with no definition just about anything goes. Ironically, a Class D amplifier is perhaps the last potential contender for the title even though there's a big D in its name. In purest form the pulse streams lack numeric value (although they can be given one). But DSD is the same and we think of it as "digital", so is a Class D amplifier digital? Possibly!

There are other forms of 'digital amplifier', those with digital inputs that are converted to analogue by a DAC for example. Arguably more deserving are those that are totally digital internally, turning all analogue inputs to digital through an ADC. This approach is becoming more popular because all sorts of tricks can be coded in: filters, tone controls and gain adjusters all come to mind, including phono equalisation curves.

I've yet to be convinced that Class D sounds better – even when done perfectly. Analogue Class A/Bs do a near-perfect job in any case, so hardly surprising. The real benefit of Class D – or Class Z or whatever – is economic and 'green-ness'. A small, lightweight amplifier that draws little mains power and costs peanuts. Like it or not, Class D makes an inarguable case and we will be hearing much more from it in future.

— Noel Keywood
Editor, HiFi World

Subscribe!
Click here to subscribe to Hi-Fi World.