For a long time now the white elephant in the room has been Class D digital amplification. In many ways Class D has been seen as the natural future for driving loudspeakers, in much the same way that electricity is the obvious fuel for powering cars.

Unfortunately, the results have been almost equally ambivalent in both cases. Digital amplifiers run cooler, consume less power and consequently, are greener than traditional amplification, which have to be good things.

With most music sources starting life as digital once they hit the microphone, it makes obvious sense to preserve the music signal in digital form as long as possible to avoid degradation.

But so far, at least, digital amplification in its many and varied forms has not been a conspicuous success sonically and is generally confined to the lower shelves powering cheap integrated systems and their ilk, where simplicity and low cost are the key attractions.

Digital future

Here, perhaps, is an exception to the rule, arguably the most striking example of its kind to date. The original and, so far, one of the few truly serious high-quality digital amplifiers was the TacT Millennium, which due to structural changes within the company has been transmogrified into the virtually identical looking and functionally similar Lyngdorf Millennium, now in its fourth iteration.

Quite how to describe the Millennium IV is moot. It drives loudspeakers and has a volume control, which qualifies it as an integrated amplifier. But it won't handle analogue inputs without external assistance (described later), and in its basic form as reviewed here, it is more of a power amplifier with an on-board D/A convertor than an integrated amplifier, albeit one that has its own volume control.

The Millennium has been around in one form or another since as far back as 1998 – more than a decade ago. But Lyngdorf claims it is one of the few truly digital amplifiers and there are good reasons why this is the case. Most digital amplifiers are only part digital, in some cases because they use a digital architecture for only part of the audio chain.

Lyngdorf's enabling digital technology called equibit, is digital from input through to output – in fact as standard the Millennium cannot even accept an analogue signal input and at the loudspeaker end of the chain, the signal remains digital until the very final stage.

This involves a simple 12dB/octave filter consisting of an inductor and a capacitor to roll away the very high-frequency digital noise above 60khz that would otherwise pollute the loudspeaker feed. Uniquely, the volume control does not attenuate the audio signal, which would reduce resolution.

Over most of its range, all it does is to control the voltage from the power supply output stage at anything upwards of three volts output, which corresponds to 19 on the volume dial. This simple, elegant solution means that the volume control is not in the signal path. Anything above this level and below the maximum output of 58 volts is handled with full 24-bit precision, with the system clock set at 352.8khz, high enough not to interfere with the audio.

At very low levels – where power supply attenuation is no longer possible – the resolution of the signal is reduced, but the volume level through the speakers is very low by that point, so the impact on the audio is negligible. By the same token, there is no amplification of the audio signal either, which eliminates another whole set of problems.