Does the NuPrime ST-10 digital amp (150 RMS) qualify as a Class D amp, or a variant of Class D??It is apparently a proprietary variant of class D.
The mention in its description of a 600 kHz switching frequency, 85% output stage efficiency, and its power-to-weight ratio (150 watts per channel, weight of about 13 pounds) all point to class D or something similar.
And this, from the TAS review that is linked to at the NuPrime site:
Although the ST-10 is a “digital” power amplifier, it is not a standard Class D switching amplifier. According to NuPrime’s owner’s manual, “Instead of the conventional sawtooth configuration, NuPrime’s patented circuit design uses an analog-modulating signal that adds neither noise nor jitter. Rather than reverting to off-the-shelf solutions, NuPrime’s in-house advances have further unlocked the switching amp’s potential without the difficulties pure digital-switching amplifiers simply cannot avoid.” The cliché that should follow would be, of course, “Not your father’s Class D amplifier.”If you look at the first figure in this Wikipedia writeup on class D amplifiers, I would speculate based on this comment that the "triangular wave generator" shown in the figure is probably replaced in the NuPrime design by some sort of signal having less abrupt transitions between its positive-going and negative-going segments. Otherwise I’d imagine that at a conceptual level the design is generally similar to what is shown in the figure.
BTW, despite the reviewer’s reference to the ST-10 as a digital power amplifier, and despite popular misconception, class D amplifiers and similar variants are not digital amplifiers. As stated in the Wikipedia writeup:
The term "class D" is sometimes misunderstood as meaning a "digital" amplifier. While some class-D amps may indeed be controlled by digital circuits or include digital signal processing devices, the power stage deals with voltage and current as a function of non-quantized time. The smallest amount of noise, timing uncertainty, voltage ripple or any other non-ideality immediately results in an irreversible change of the output signal. The same errors in a digital system will only lead to incorrect results when they become so large that a signal representing a digit is distorted beyond recognition. Up to that point, non-idealities have no impact on the transmitted signal. Generally, digital signals are quantized in both amplitude and wavelength, while analog signals are quantized in one (e.g. PWM) or (usually) neither quantity.Basically, class D is an analog process.
Regards,
-- Al