With the unstoppable advance of CD, passive preamps are becoming more and more popular. And NVA, one of the first companies to introduce the idea to the UK, has just brought out its latest model.
To help me evaluate the passive preamp and Phono 2 disc stage amplifier, NVA supplied a complete amplifier system, including a pair of A80 mono power amplifiers and even their own LS1 loudspeaker cables. The Phono 2 disc stage has its own external dual-rail power supply and is best regarded as an optional extra to the P50. Most passive preamp buyers are wholly CD-oriented: I'm not. I want to be able to play records too.
Over a period of several weeks I used the P50 preamp and Phono 2 head amp both within this system and with a variety of source and amplification components from other manufacturers. The final listening session took place using an Arcam Delta 170 CD transport with Micromega Duo BS converter, and my regular Linn turntable, the NVA amplifiers driving Naim SBL loudspeakers. I think it's fair to report that overall `the amp done good!'
It's obvious listening to the NVA combination that the company's design philosophy is based on information retrieval. That's not to imply that there's any lack of cohesion or musicality in the amplifier's presentation, simply that the P50 scavenged all the minutiae you can imagine. With a good Compact Disc player upstream, one that was able to reveal nuances and low level information, the P50 gave a graphic account of what was present on discs. It was similarly dextrous when handling dynamic variations in the music.
This transparency proved to be a double-edged sword in some circumstances. By stripping away the masking with which many conventional preamplifiers sweeten a CD player's rough edges, several sounded distinctly uncomfortable. Neither did the NVA A80 power amplifiers suffer from undue warmth or euphony, so take heed those who would front these amps with a CD player which is anything less than impeccably behaved.
Record-playing activities proved rewarding using various moving coil cartridges. Audio Technica's OC range, including the AT-OC10, worked particularly well, offering just the right amount of gain. Given such a cartridge the Phono 2 displayed the familial propensity for unearthing tiny details from within a busy mix, at the same time retaining a good overall grip and perspective on the music.
There was no obvious attempt to impress by selectively tossing titbits at the listener; the NVA disclosed such information completely within the context of the performance. Acoustic guitars illustrated this especially well, with plectrum strikes and fretboard squeaks fully integrated into the sound of the instrument and not flamboyantly detached from it.
Some listeners might be impressed by an artificial approach emphasizing detail in an impressive but, to my ears, inaccurate and ultimately annoying way. They would not appreciate the integrity of there NVA amps. Further to the amp's credit, despite this welter of information, it never sounded relentless, even when pushed hard: and the system's gusto and zeal tended to invite realistic playback volumes.
The P50 preamp made an excellent companion for CD and LP, hiding next to nothing and not stamping a sonic footprint onto recordings. The Phono 2, which made it `complete', did justice to a range of good cartridges. But something tells me that the majority of P50s will find their way into the homes of CD fans. I just hope that their players are good 'uns.
Source: Audiophile (August 1991)
Why go passive?
With the increasing use of CD as primary source, the need for traditional pre-amplification recedes. Line-level sources such as CD, tuner and tape normally have sufficient output to drive power amplifiers such as Roksan's Artaxerxes and NVA's own Phono 2 can be used to feed passives. All you need worry about is the number of inputs provided since a passive preamp is simply a potentiometer placed between the source component and the power amplification.
Proponents of passive preamps point to their simplicity; those who argue for traditional active preamplifiers point to potential difficulties interfacing passive preamps with certain kinds of interconnect cables and power amps which may present the wrong electrical characteristics. There is truth in both arguments.
NVA claims to have been one of the first manufacturers to market a passive preamp way back in 1983. Interestingly, the development was not driven by the widespread usage of CD, as the date might imply: according to NVA's owner and designer, Richard Dunn, `It has always been our view that circuitry should be kept as simple as possible. We developed a passive simply because it offers better sonic performance.'
When NVA switched to a passive preamp (with phono stage, of course), the company also changed the input stages of their amps to offer the correct load to the potentiometer.
NVA's P50 and P80 are built into an aluminium box, epoxy glued together - NVA is part of the school that believes magnetic boxes are a bad thing - that most people either love for its solidity, or hate for its Spartan simplicity. And, by gluing rather than screwing, even the tiniest eddy currents are eliminated.
Inside, there's no circuit board, just a potentiometer, a very high quality switch and some expensive silver wire.
The other main design aim was to provide good earth paths. Ground plane earthing is used, which the manufacturer believes is superior to the more fashionable star-earthing used in many better known amplifiers.