NuPrime Evolution STA

Allow us to introduce you to latest iteration in NuPrime’s innovative amplifier range. The Evolution STA (NZ$8500 incuding GST & delivery) is an enigmatic and interesting beast to say the least. It’s the most substantial single component NuPrime (and previously NuForce) have ever produced and not only builds upon the technologies within their existing suite of Class A/D hybrid designs but also introduces a novel approach to reducing distortion.

If you browse through our pages and NuPrime’s own site it’s obvious that they have a lot of amplifier models and I’ve written extensively about almost all of them. Dig deeply and you’ll even find some of the earlier NuForce models so we now have multiple points of reference. Not to mention years of experience with numerous NZ made and imported brands.

The rationale for the Evolution STA is simply to deliver the level of performance of the Evolution One mono amplifiers in a single box which is more affordable and hence brings the best sound to more people. The STA fulfils this promise and there are some aspects in which it excels, improving on the Evolution Monos.

A good question is how this fits in with the breadth of the NuPrime range and divergent characters we now have from the Evolution, MCX and AMG series. I’ll deal with this comparison shortly.

A natural progression

The Evolution STA is a natural progression from the original ST10 and is intended to build upon the best of both this model and the new AMG STA. So it shares a lot of qualities. The ST10 has also been available in a better and more powerful mono version, and appears that these may have been the starting point from which the Evolution STA has sprung from rather than trying to compress two monos into a single box.

It’s when we compare the NuPrime to other conventional brands of amplifiers that things get interesting. With solid state Class A and Class AB designs (and also tube amplifiers) which have been around for a long time now, just about every permutation of design has been tried and there isn’t much left to do other than tinker with component choices – which traps most in a spiral of incremental improvements inevitably tied to price increases.

While NuPrime aren’t immune to these pressures, the relative newness of Class D design has given much more scope to find different ways of doing things and so it’s possible to make quite big improvements without dramatically increasing costs.

And to a large extent this is what’s happened with the Evolution STA – NuPrime claim a break through in their design which they describe as ‘Only Distortion Cancellation (ODC) ‘

‘Nuprime’s ODC Class-D design derives the error signal from MOSFET devices and the output filter circuit directly, significantly reducing the negative feedback signal, which resulted in a substantial reduction in distortion THD+N of 0.002% @1kHz(5W), and less than 0.005% THD+N at 1KHZ (2W-100W). This breakthrough improvement in Class-D design resulted in a natural and pure sound characteristic’ for the technically minded.

I’ve been in contact with Jason (NuPrime CEO) to learn a little bit more about how ODC fits in with the previous developments that have featured in the original Evolution One mono amplifiers and the more recent AMG STA stereo power amplifier. 

The improvement made by the ODC design, in terms of distortion reduction,  is an order of magnitude greater than the previous high water mark set by a combination of the 700kHz switching speed and 1M Ohm input impedance.

It’s not unreasonable to expect any serious amplifier to have vanishingly low levels of distortion so is this claim valid? 

Think about this – in your own experience it’s likely you have heard components that sound significantly different from one another – some sound better, some not so much. Even within NuPrime’s own range we can easily hear markedly different characters to the sound. There can be additions, omissions and interactions both produced within a components and also induced by outside sources – ie interference. These deviations from the original sound are, by definition, distortions. This isn’t always a negative as some euphonic distortions can actually seem to make things sound better.

What you’ll hear

So we know that all amplifiers do in fact distort sound to some extent. But what does a significant reduction in distortion actually sound like? This can actually be quite hard to define as it’s often an absence of something – not an addition.

However, in the case of the new Evolution STA, it is readily apparent. From the first time you turn it on there are immediate, obvious qualities. The noise floor is really, really low and even when playing quietly you’ll hear a whole lot of details that simply weren’t there before having being previously obscured. A fuzziness you might have previously accepted as part of the recording disappears and there’s a clarity to each and every note. Stereo imaging gains considerable definition.

The Evolution STA is tonally the most neutral design yet from NuPrime, poised and even handed. Sure footed and precise without being analytical, the NuPrime Evolution STA reproduces vocals with exceptional clarity; there’s no sibilence or glare.

The Evolution STA sounds marvelously energetic, expressive, and utterly coherent with immense neutrality but without tipping over into leanness or coolness. The amp is also very linear and quite detailed but not revealing to the point of being analytical, let alone clinical. First and foremost, it paints the complete musical picture while sounding nothing like your typical Class-D amplifier.’ Christiaan Punter.

Having seen the inside of every NuPrime amplifier and a whole lot of other brands there really aren’t any surprises for me. But for you it’s worth noting the almost complete lack of heat sinking that differentiates NuPrime from almost every other amplifier – the STA runs cool even with no venting. This in turn means the power supply isn’t heating your room up and the amplifier need be no bigger than it has to be. So while the box that arrives at your door will still be a substantial 14kg, it’s all about delivering power to your speakers

Nuprime Evolution STA rear panel

There are some nice little detail touches – high quality ETI binding posts, Furutech input RCAs and  balanced sockets. The case work is the now classic slimline NuPrime ‘Stealth’ profile and specially made conical isolation feet.

Most of the weight is attributable to a 550W high-power ultra-thin toroidal transformer which occupies the greater part of the STA. If you know what you are looking for you’ll also be able to identify some serious power filtering between the transformer and AC socket.

A direct comparison to the Evolution One mono amplifiers is largely academic as these have been quietly run out with the introduction of the STA so it is effectively a replacement. Having lived with the Evolution monos since their inception I can tell you they are broadly equivalent. Yet there are subtle differences. Some of these you can pick up in the specifications, such as sensitivity, gain and rated power output.

But the refinements in circuit design of the STA ameliorate most of these differences and in some areas such as absolute accuracy I think the STA is just a little bit better. So to have this and an effective NZ$5000 saving in cost has to be a good thing.

Given the already generous power output and cool running nature of the Evolution STA there was little to be gained by producing a more powerful mono version other than doubling many costs such as packing and freight, chassis and many internal components. Higher power is also not without its own design challenges. And if you continue reading you’ll learn that NuPrime do in fact have plenty of mono options including a much higher power model – the MCX-1

Context is everything

The accuracy of the Evolution STA does however shine a light on the rest of your system. The quality of source you match with it, be it analogue or digital and what, if any, preamplifier you use will contribute greatly to the end sound. The differences cables make will be thrown into sharp relief and this does include AC mains cables. The STA will magnify any improvement you make in this regard but it won’t make up for noisy, low resolution or just ordinary sounding inputs.

NuPrime’s matching Evolution DAC is an obvious choice.

During our initial listening, we were also lucky enough to have the new Lumin P1 network player – this is an unarguably mighty component which has allowed us to appreciate what NuPrime are doing all the more.

On the analogue side, NuPrime’s own AMG PRA preamplifier remains a personal favourite, and the added richness and scale it produces again matches perfectly with the Evolution STA.

On the speaker front it’s an entirely different story. Assuming you have the input side of things taken care of the Evolution STA can make even modest speakers sound like the voice of god. It’s very seldom anyone hears all that their speakers are capable of. The speakers in most systems are limited by the lack of power, inadequate control and amplifiers that simply struggle to drive the load while adding a pile of noise and distortion. While not that many speakers are rated to the 230 watts for 8 ohms or 310 watts for 4 ohms that the STA is specified at it would be a very rare event for you to actually use the full output and even then, it’s distortion that damages speakers, not clean transient power. I’m actually rather taken by how good the STA sounds with the little Sonus faber Luminas. It’s all about headroom.

Larger and more ambitious speaker systems tend to put out more sound and while they are often more demanding in terms of the complexity of their load, the Evolution STA is right up to this task. It’s always important to remember that quality and quantity are not synonymous. But if you’re into death metal and 230 watts seems like a drop in the pan we do actually have the answer. Stay with us on this one.

So, while getting a feel for the STA, we have swopped through several different systems. As expected the Evolution does mature through an extended warm up or run in period. This will be at the very least, 300 hours and given our previous experience with the monos there are still gains to be made at up to 6 months of normal use. The initial obvious neutrality can feel restrained and a little flat but rest assured, the presentation becomes more fluid and open as time goes on. 

It’s also important to understand the NuPrime Evolution STA is somewhat different in specification to their other NuPrime models – the input voltage is higher and gain lower so when plugged into a system, you’ll have to turn the volume control up higher to get the same sound level. But this also helps explain the lower distortion levels, improved transparency and lower noise floor. It means it’s far less prone to overload from ‘hot’ sources and will take wide swings in dynamics in its stride.

Another side benefit of the new design is that it’s far less likely to be affected by input noise, especially when the input ground and AC ground are not connected. In many systems this will be manifested by an eerie and open silence where there was previously an opaque background. You’ll know it when you hear it.

Defining the character of the new Evolution STA is surprisingly difficult. This may be because the NuPrime have achieved what they set out to do in building a truely neutral and transparent power amplifier. The enigmatic nature of the STA is compounded by the fact that like every power amplifier, what you get out is very much dependent on the quality of sound coming in. In the right system, the Evolution STA will show its full worth and potential.

The ideal power amplifier has been described as ‘a straight wire with gain’. This is a purist notion that isn’t actually valid for most other components as is often processing of some description – such as digital to analogue, and RIAA. But for a power amplifier it does make a lot more sense as it has a much more tightly defined task. The STA is getting very, very close to this ideal.

Where the Evolution STA fits

The rapid expansion of the NuPrime ecosystem gives you an almost bewildering array of choices so let’s take a moment to look at the amplifier range as a whole which will also give a better context for where the new Evolution STA fits in.

If we look at stereo power amplifiers there is a clear hierarchy. The entry level ‘9’ series STA-9, the massively powerful MCX-2, the seductively fluid AMG STA and now the Evolution STA. 

The Evolution STA betters all of it’s more affordable siblings while maintaining, and actually improving upon the neutrality and transparency of the Evolution One Monos.

Given the 3 more affordable options are around 1/3 of the investment and size this is not all that surprising. But remember with both the STA9 (and new STA-9X), and the AMG STA, you are able to bridge and turn each into a significantly more powerful and better sounding mono amplifier with the flick of a switch. And the MCX-1 750 watt mono power amplifier is another option.

So you can see that NuPrime are now delivering multiple paths, each with a distinct character and flavour, to reach your own state of audio nirvana.

The affordable entry STA-9 remains a remarkable achievement, a classic of the NuForce/Nuprime design story combining a warm rich and powerful sound (120 watts per channel) in a compact cool running and modest box. A bridged pair delivers 290 watts into each speaker. It’s an ideal introduction to NuPrime but also good enough to be the penultimate amplifier for many systems.

The MCX-2 is the most fun it’s possible to have in a single box. The use of an outrageously powerful 1000 watt switched mode power supply and modular construction make this and the even more powerful MCX-1 perfect for any rock enthusiast. Deep bass, breath taking dynamics and an intentionally strong midrange presence will make your speakers light up. 

The AMG STA is defined by a fluid and relaxed sound that confounds anyone who expects solid state and Class D to take a back seat to the performance offered by vacuum tubed products. Yet the AMG is more powerful and offers greater resolution and lower noise floor. A bridged pair takes the performance from sublime to spectacular. 

The Evolution STA manages to improve on all these options with precision and a subtle assurance. In the few weeks I’ve been listening to the new Evolution stereo power amplifier I think I’ve found it’s essence but am still well short of establishing the ultimate level of performance. An amplifier this good will never be the weak link in a system and so it’s not unreasonable to  assume that you’ll gradually improve the components around it. This makes the Evolution STA a real long term investment that you’ll enjoy not just for the moment but even more over the coming years.