The NVA AP50 integrated amp
is a return to British
solid state minimalism
After it's burned in for a few weeks, the AP50 reveals surprising qualities like smoothness to rival vintage valve confectionery
This amp is so cleanly styled that it'll confuse those introduced to audio through an A/V receiver of post-1990 construction. Then again, it's not surprising, as Richard Dunn is the industry's self-appointed pomposity filter, author of numerous missives protesting one thing and another. But he does practice what he preaches, and the AP50 is as free of taurean faeces as is possible without eliminating basic operations. Even the on-off toggle has been relegated to the back panel, which houses only the requisite (gold-platted) sockets for the six sources, the tape loop ingress and egress, and speaker sockets which accept only the near-to-extinction banana plug. The front panel bears but two large knobs, one a nicely weighted device for altering level, the other for selecting the source. As the front NVA panel is made from black perspex, NVA has used this to good effect by including a tiny red LED to indicate on/off status in a most tasteful manner. But it won't cause palpitations among those who get their rocks off by switching off the lights to watch their hi-fi systems luminous capabilities. All we're talking about is a tiny red dot.
Er, that's it. The unit is so clean and simple and nicely finished that, were the dealer to cover the NVA logo, you could easily mistake it for a Densen integrated amp or some other device of the Scandinavian persuasion. The amplifier is a tonic for those fed up with clutter, a throwback to 1983 and the days when anyone using a source other than a turntable was deemed an untermensch. Only this is 1996 and Dunn has a wicked sense of humour: phono is optional.TECHNOLOGY
In the form which arrived for the review, the AP50 bore six identical line inputs, hardwired to the selector switch. NVA - as cable-sensitive a company as I've ever faced - uses silver alloy with a PTFE cover at this stage. The output of the source switch is fed to the volume control and tape sockets, again via silver wire. The potentiometer is an ultra high quality 'cermet' type using precision metal film resistors 'as a bypass to simulate a log law'. The signal is fed to the amplifier PCB again through hard-wired silver cabling.
There's a list of acceptable wires which accompanies the AP50 naming seven precise makes and models of wire at the top of the tree (two from NVA, all types of DNM), and a roster of 22 others which pass muster. And just in case you think that Dunn is kidding, the sheet also states categorically that, 'If any other cable than the recommended are used it will invalidate our guarantee'. And should you entertain the notion that such a stipulation is illegal, I think you'll find that the warning qualifies as valid instructions for use, and to ignore it would be like expecting a car manufacturer to pay for a new catalytic converter when you've been using leaded petrol.
Although I'm loath to cite a revival in passive pre-amplification, despite this technology rearing its head in all manner of unlikely places, the front-end of the AP50 is completely passive, with Dunn pointing out that there's a wee trade-off in using the cermet pot. Apparently, the cermet tracks are not as smoothly finished as conductive plastic film or carbon tracks, so there's a form of 'surface noise' just audible when you alter the volume. But Dunn argues that cermet provides far better sound quality than alternatives, so the residual noise during level changes is a small price to pay for sonic superiority. And besides, you do your listening when the levels are set and the rotation has stopped. (No, let me guess: There's a rare breed of Tasmanian audiophiles who listens to music with the volume constantly changing...)
Because it's fed by a passive pre-amp, the input stage of the power amplifier section has minimum inductance and capacitance, and a current mirror is employed to guarantee that the volume rails track each other correctly. Overkill has been applied in the power amps driver stage in that both the current and voltage amplifiers use devices hefty enough to act as output transistors; the actual output devices are 12 amp Darlingtons, two per channel and responsible for its 60W/ch rating.
NVA also eschews in this product any form of protection circuitry, which should be kept in mind when you first read the detailed instructions and warnings of locusts and boils should you behave in an unnatural manner. Grounds for turning you into a pillar of salt include short circuits, bi- or tri-wiring, running greater than 10 meters, using 'unapproved cables', high capacitance or Litz wires, or listening to Babylon Zoo CDs. Indeed, so fearful was I of incurring the wrath of Dunn that I didn't stray from using the supplied NVA cable.
Again in the interests of sound rather than 'unconditional stability', the AP50 employs the minimum number of capacitors, no inductors, low negative feedback, and Class AB operation. A 300VA toroidal transformer with a 25 amp bridge rectifier and a unique filtering system for the power supply. Even the case is slightly odd in the interests of sonic excellence; it's non-magnetic, glued together, and insulated to prevent static charge problems, and to stop induced circulating currents. Hell, Dunn has filled a 12-page 'white paper' with NVA philosophy, an audio Mein Kampf which makes fascinating reading if you don't mind being beaten over the head with an audio designer's beliefs. Fortunately for Dunn, he tends to make sense. Which is why the AP50 is such as killer
To everyone's dismay, there are dozens of amps out there for circa £520 which do wonderful things. Expand the sector to embrace £450-£700 and you find all sorts of goodies, including the delicious Densen Beat, some entry-level tubeware, British perennials, the better Japanese integrateds and limitless second-hand opportunities. Clear winners that obviate the existence of all others? That's wishful thinking on the part of magazines which gives awards for 'Best In Its Class'. Such a beast cannot exist because there's no such thing as a universal solution. Which is why cranky hardware like the AP50 actually has an easier time in the market than any of the half-dozen top-rated Asian 50-watters which compete for the exact same customer.
Dunn's logic is as transparent as the amplifiers sound: if you lay down a specific set of rules, you've (1) focused on the customers prepared to meet those criteria and avoided the time-wasters and the 'ineligibles', and (2) ensured that the amplifier will be used correctly. Admittedly, such an approach in anathema in business terms: it's the deliberate limiting of a product's appeal. But it doesn't half make life easier all round. And you customers will know exactly what they're getting.SOUND QUALITY
If a gun were held to my head and I was forced to cite but one trait which defines the sound of the AP50, I'd have to say it's the overall silkiness
In the case of the AP50, it's an amplifier that - without drama - gets on with the job. It drove a weird mix of speakers (despite my ignoring the command to avoid speakers which might possess 'high frequency notch filters'), including the original Quad ESL, Sonus Faber Concertinos, LS3/5As, Boleros, and the Rega headphone adapter, and never less than satisfactorily. The unit never showed signs of distress. Asked to play loudly, it rocked. Asked to play softly, it did so with the dynamics intact. But it had a few secrets which it didn't yield so readily, and I was misled into thinking that the AP50 was simply a minimalist alternative to the Rotels, Pioneers and NADs of the world, or yet another Britamp to place alongside Arcams, Naims or Audiolabs.
Big mistake. After it's burned in for a few weeks, the AP50 reveals surprising qualities like smoothness to rival vintage valve confectionery. Although it's most evident in the region normally plagued by digital coarseness, this refinement also blessed all manner of vocals with a resistance to the shame of sibilance. If a gun were held to my head and I was forced to cite but one trait which defined the sound of the AP50, I'd have to say it's this overall silkiness. Which is not something I'd expect of a mid-priced, solid-state integrated amplifier.
Whatever Dunn's current feelings about soundstage and imaging, the AP50 is almost Yank-like in its three dimensionality. It's about as far from the 2D sound favoured by UK flat-earth amp builders as is possible for such sane money, and this begs the use of precise performers (in the imaging stakes, that is) like small two-way systems of the LS3/5A calibre. Perhaps there was some sort of mismatch with the Quads, but imaging was the one area which wasn't exploited when the AP50 faced the legendary electrostatic.
Sticking with the kind of two-ways likely to be used with an affordable solid-state integrated, I was overjoyed to learn that the AP50 avoided, like the plague, the kind of heightened hygiene, that aggravating sterility which too wham-bam-thank-you-ma'am sessions suggest is true transparency. The AP50 strips away nothing, and I implore you to audition it with rich vocals if you want to learn just what it can do. Arm yourself with some Nat King Cole, Keb' Mo', Johnny Rivers, or Howard Tate to hear the most detailed textures, and Nanci Griffith or Joan Baez to hear unbridled clarity without glassiness. And that's one hell of an accomplishment at the price.
AUGUST 1996, HI-FI NEWS & RECORD REVIEW