George is correct in categorizing the Technics SE-R1 as a class D amplifier. It uses a pulse-width modulated switching output stage, and it is therefore a class D amplifier by definition. Various architectural differences that it has with respect to most other class D amplifiers, including the ability to accept digital inputs from a mating Technics preamp and keep the signal in the digital domain until it is converted to the PWM signal that controls the output stage, do not change that fact. Statements such as the following, which appeared in this TAS review, are misleading and incorrect in drawing a distinction between class D and digital amplifiers:
Regards,
-- Al
Indeed, this is not a traditional Class A, Class AB, or even Class D amplifier. Rather, it is a rare breed known as a “digital” amplifier....What would be correct would be to say that a "digital amplifier" in this context is a form of a class D amplifier. And as such, like any other class D amplifier its design must address the issue of output stage switching speed. And the sonic consequences, if any, of the low pass filter at the output of the amp for which the required bandwidth is a function of that switching speed.
As with Class D amplifiers, digital amplifiers use a switching output stage; however, they accept digital rather than analog input signals. These “digital” amplifiers take in the pulse-code modulation (PCM) signal from a music server or other source and convert those audio data to a pulse-width modulated signal. This PWM signal then drives the output transistors, just as in a Class D amplifier. The difference between a Class D amplifier and a digital amplifier is that the digital amplifier accepts digital data rather than an analog signal.
Regards,
-- Al