PrimaLuna is one of several manufacturers to have wholeheartedly adopted the principle of designing in Europe and manufacturing in China.

The company is based in Holland and specialises in valve equipment, which it divides into two ranges, Prologue, and the rather more upmarket Dialogue.

The Prologue models share a case design, which must help keep costs down and partly explains the rather untypical dimensions of this unit.

Unusual design

The other part of the explanation is the use of valves. Small-signal valves in the output of a CD player are nothing new, but most are physically small and will fit in a much lower-profile case than this.

PrimaLuna has gone one further, though, and included valve rectifiers, which are considerably larger bottles. Until recently, valve rectification was strictly the stuff of deep, retro, kit-built electronics, but renewed production of the relevant valves has brought it back in to the real world.

It is claimed to be worth the extra trouble (and it's a lot of trouble, necessitating extra transformer windings for a start, never mind the extra space, valve sockets, etc.) because valve rectifiers typically produce less switching noise than solid-state types, reducing internal interference.

Even more surprising than that, though, is a valve in the digital section of this CD player. PrimaLuna claims this is a first and we've certainly no memory of it being done before in any production CD player. Although one might ask, just what can a single valve contribute in a digital circuit with its hundreds and thousands of switching elements?

Master oscillator

The answer is that the valve in question, a tiny single triode concealed deep inside the player, forms the heart of the master oscillator, which controls the digital-to-analogue conversion process.

PrimaLuna has an interesting justification for this, which is that transistor oscillators can contribute phase noise (jitter, in everyday audio parlance) because the transistors used have more bandwidth than is required to make the oscillator work.

We're not absolutely convinced by this, since any well-behaved reference oscillator owes almost its entire performance to the passive component(s) at its heart – a crystal, in this and almost every CD player – but by the same token there's no reason to assume the valve won't work very well in its novel application.

Apart from the listening, of course, the proof of this should be in the jitter, which PrimaLuna claims is particularly good by current CD player standards: again, we can't entirely concur, but only because many CD players in current production have such good jitter as to be practically unmeasurable.

Sound limits

The transport chosen by PrimaLuna is an audio-only one, which gives the player quick loading and mechanically quiet operation.

The valves sit above it, while the rest of the audio circuit is beneath the rear enclosure, which houses the mains transformer. It's not all valve electronics, either – the critical digital-to-analogue converter chip is a modern part and it is connected to an asynchronous sample rate converter, while the analogue filter stage uses op-amps.

These are the once-derided 5534, an audio veteran dating from the 1970s, which ten years ago was completely out of fashion in upmarket audio, but is now back on the shopping list for many designers.

That said, PrimaLuna doesn't claim that the 5534 is the ultimate in anything and has taken another unique step in making available an op-amp upgrade board. This is particularly clever: the (four) op-amps in the Prologue Eight, mounted in a line, in sockets.