NuPrime Sta-10

Incredible performance at an incredible price

Review sample provided by Dimex
Retail Price: 1595 euro

Let’s go crazy and start with the conclusion for once, as the following text on the NuPrime product page pretty much sums up how I feel about this amp:

“NuPrime’s sonic character stands well apart from – and indeed above – the soft, cushy sound we often associate with most tubed amplification and the dry, clinically edgy sound we often associate with solid-state and switching technology. Rarely does an amp achieve an ideal balance of richly textured timbres and harmonics, bottom-end authority, startling dynamics, exquisite low-level detail, and a fully revealed, fully dimensional sound stage against a backdrop of mile-deep silence.”

But do read on to learn more, and to find out exactly how the ST-10 performs with various speakers and how it compares to various other amps.

 

Unique Sonic Characteristics

NuPrime have unravelled those parameters with which they can tailor each product to have unique sonic characteristics. Opinions and personal taste will forever differ, and so there will always be those who want a smoother, creamier, warmer delivery, for example to add some extra romance to vocals. While the ST-10 is a clean sounding amp, NuPrime also offer creamier sounding amps, should that be desired. The choice is with the customer, and this is quite unique.

By cleverly combining the various parameters precisely as required, NuPrime can pretty much offer custom solutions. For example, to quote from the amp-comparison white paper:

“We advise customers to make their selection based on sonic preference and usage scenario. If you watch a lot of movies and enjoy to a wide variety of musical styles, you might prefer MCH-K38. If your thing is classical music in its entire vast and dramatic splendor, you will likely go for Ref 20 or ST-10. Conversely, if vocals are your passion, you will likely prefer the MCH-K38 or STA-9.”

This all lines up perfectly with the adagium that I keep using in these pages which is that audio equipment selection is relative, and very much dependent on system synergy and personal preference.

Technical Aspects

There are various manufacturers that issue amps based on Class D amplification. Usually they employ modules such as ICEpower, Hypex, Pascal and then they may apply some tweaks. NuPrime is one of the very few companies left that still do original R&D on class D designs. They designed their own circuits and implement them as cost effectively as they can, while maintaining very high performance.

According to the manufacturer, NuPrime amps have no phase shift. Many amps use output filters that create phase shift. When phase shifts, spatial information becomes inaccurate. Most amps present phase shifts of better than 45 degrees at 20 kHz, heading toward 90 degrees as frequency increases. NuPrime amps cancel these distortions owing to a unique closed-loop design producing ZERO phase shift across all frequencies. Another interesting aspect of the NuPrime implementation is that instead of the conventional saw-tooth configuration, the NuPrime circuit design uses a naturally occurring analog-modulating signal that adds neither noise nor jitter.

There is a lot more to write about Class D in general and the NuPrime implementation in specific but that’s already done in many places as well as on the NuPrime website, for example in their Learning section.

One important matter that I want to (again) stress is that class D is not necessarily Digital. Rather, class D describes a switched output stage working according to the PWM principle, which is very much analog in itself. Extra steps can be taken to enable a digital input but the amplification part is still analog.

Above and below: very clean packaging with infinitely re-usable magnetic lid

Wilson Sabrina

The NuPrime ST-10 is a tiny amp. If I did not know better then it would be easy to assume that it is underpowered for any Wilson. The truth could not be more different: the ST-10 really brings the Sabrinas to life! Transient crispness and dynamic impact are really startling, better even than with any of the other amps that were used during the Sabrina review. Bass is also incredible, not in a big and fat kind of way but because it is tuneful and articulate with just the right amount of pressure. Meanwhile the NuPrime’s very natural tonality helps the Sabrinas sound timbrally more believable.

Timbrally the ST-10 is a mix between the Ayre VX-5 Twenty and the Bryston 3B cubed but with more accurate bass than the Bryston and more impressive dynamics than the Ayre. From memory it does not have the fluid yet synthetic nature of any ICE power amp that I tried but it does sound a little like the Jeff Rowland 525 which uses as Pascal module, in terms of solidity and sonority. The 525 however never really came to life during my tests, which the ST-10 absolutely does, and with gusto! The NuPrime really presents music with a life-like, as well as live-like character: tonally pure, direct-coupled and very expressive. Treble performance is slightly rough though. Not at all harsh, just seemingly not as fluid and hi-res as I’d like it to be. Or could it be that the ST-10 presents treble just the way that it is on the recording, meaning that many other amps add more fluidity than they should? I’d be tempted to say that this is not very probable, but when listening to the ST-10 on the Apogee Centaurs or the Gustavsons, and playing a selection of old smooth jazz, it’s just great, with treble that is as fluid and airy as it needs to be.

Apogee Centaur

For more than a decade, the Centaurs were used with Jeff Rowland model sixes by their owner and dear audiofriend JW. The sixes are true high end amplifiers that in their day cost around 15.000 euro. This is almost 20 years ago so go imagine what they would cost now. Ok, so the NuPrime ST-10 is not the equal of these Rowland monos, but as the Rowland sound has slowly evolved from very creamy to more neutral these days, the ST-10 actually comes closer than you’d think. Although the ST-10 does not have the Rowland-typical rose-tinted, extra smooth character, it does perform better than the sixes in some aspects.

Connected with current edition Transparent Super XLR interlinks and Transparent Super speaker cables I listened to Joyce Cooling’s Cameo and then Chris Standring’s Blue Bolero, and it really sounded great! Maybe I did not hear the same amount of treble air, but treble was definitely airy and most definitely not edgy or bright. The Centaurs really are not tolerant at all in that respect, so if there was any harshness added by the amp, the Centaurs would have let me hear this. Listening to more music I do hear that not all music is produced equally smoothly, but the NuPrime is always honest. Even when playing dry recordings and when the treble sounds square-ish, still all you do is take note of it and move on, because the sound is otherwise so engaging. As expected the bass was just perfect again, but not expected was the lifelike tonality and the liveliness and involvement in the midrange. This was a real toe-tapping performance. I was actually more involved emotionally using the NuPrime because of this, even if ultimately it is not every bit as refined and hi-res as the Ayre.

The ST-10’s very direct and highly revealing delivery may not be liked by everyone though, but that’s a matter of personal preference. And as mentioned, should a warmer delivery be required then NuPrime also has several richer sounding amps in their portfolio.

Really the only aspect of the ST-10 which makes it less than ideal for me is its treble behaviour. While absolutely never harsh, it comes across as lower in resolution and lacking the air that my Jeff Rowland model 6 amps had, and which the Rowland 625 s2 and Ayre VX-5 Twenty also have. But these are just boxes that I want ticked, being the perfectionist audiphile that I am. For the most part this is academic, as the musical message is certainly not hampered by such aspects.

Wilson Watt/Puppy 8

Switching from the Sabrina to the Watt/Puppy 8, the ST-10 is still completely in control but without sounding overly controlled. Once again the midbass and lower midrange are the areas that stun me most. Also with the Watt/Puppies the amp seems to have plenty of reserves and is still happy to play as loudly as I ask it to while retaining posture at all times. It simply does not compress nor does it become shouty. Quite an achievement for a 1500 euro amp!

Apogee Duetta Signature

Since we’re in fun mode anyway, let’s see what the ST-10 can do with the recently re-re-furbished Apogee Duettas. After listening to them with the Ayre VX-5 Twenty, the NuPrime ST-10 comes in. Disrespectfully placed right on top of the Ayre and connected with the same interlinks, power cable and speaker cables, the ST-10 was just switched on from cold. Rightaway the most striking feature again is its sonorous sound. It’s not a smooth and “BIG” sound in the Bryston kind of way, nor creamy classic Rowland kind of way, but something I can only describe as a clearly defined and upbeat lively ballsyness.

Coming from the Ayre it is also evident that the NuPrime does sound less finely resolved than the Rowlands and the Ayre, but with the Apogees it definitely does not sound dark, just less fluid. Also with the Duettas, it’s not rough or harsh and certainly not processed or synthetic, and while treble seems to be lower res, the bass is actually very highly textured and precise. This again raises the question whether the NuPrime is actually lower res in the treble or most class A/B amps simply add fluidity that isn’t in the recording? If you ask me this is not a question that must be answered. It’s simply a matter of preference. I guess that if you want very accurate bass, you also get very accurate treble, for better or for worse.

The Apogees are certainly under control, and with power to spare. Also evident is that this class D amp absolutely has no issues passing along the music’s lyrical qualities. The amp gets right to the heart of the performance. It doesn’t distract itself with fine details too much but definitely deliveres the musical message with gusto.

Changing the Belden + IeGO powercable for a Cardas Clear Beyond definitely brings some welcome changes. Although now slightly less controlled in an absolute sense, the overall sound is gentler and more fluid and yet still very sonorous. Changing the Cardas for a Furutech FP-TCS31 adds more “gravy” so to say, to create a creamier sound, which works very well with slower music like soul. With rock music however I start to long for a little more bite, and the more direct-coupled, timbrally more acoustical portrayal with the Cardas and even more so the Belden. The amp certainly does not require high end cables to sound its best, but it is interesting to know that it can be tweaked, should this be desired.

Gustavson LS-One

With the very efficient Gustavson speakers, the NuPrime provides a superbly intimate midrange, and quite unsuspected, smooth, fluid and airy treble. This was unsuspected because the NuPrime’s treble comes across as being a little rough with the Apogees and the Wilsons. The ST-10’s bass is faster and more articulate than that of the Brystons, and acoustically more convincing to my ears. That said I can imagine some listeneres preferring a warmer sound with these speakers. Even though each of my friends agree with me that the ST-10 has remarkably natural timbre and impulse behaviour to challenge the best tube amps we heard, some of them still prefer the warmer, richer sound of tubes, or the Brystons, especially when listening to vocal music. JW even happily admits that even though he sees the benefits, he has been listening to a fair amount of smear for so long that he finds it difficult to get used to such a clean sound. For upbeat music with lots of rhythm and percussion we all agree that the ST-10 is most fascinating and involving.

Vivid Audio Giya G3 s2

Now for the most unlikely combination of all: a 1500 euro NuPrime ST-10 with 35.000 euro Vivid Giya G3’s. Probably nobody would even think of even trying this but I am happy to confirm that the humble ST-10 drives them splendidly! The Vivids were delivered for review along with Mola-Mola Kaluga power amps and those amps really are worthy of their reputation. The main difference between these two very differently priced amps is the same as I have described further above and concerns ultimate resolution, the NuPrime just not reaching the insane levels that the Mola-Molas do. Futher, there is a difference in timbre, bass fulness and ultimate transparency.

The Vivids really are very revealing speakers, perhaps even more so than the Wilsons, and it is with these speakers that I can most clearly hear that the NuPrime has some added character that the Mola-Molas do not. The NuPrime has a fuller tonality throughout the midbass and lower midrange which I actually like and prefer with some speakers. One might call it a colouration, another might call it more natural. In any event whereas many other class D amps sound quite thin, this extra body also adds to the ST-10’s more natural timbre.  The Mola-Molas by comparison are ruler-flat and much more anonymous, which makes them ultimately more universally applicable. Now whether or not this is a pre or a con is a personal matter. While I appreciate both approaches, as well as the sound of tubes done well, many of my friends are more biased toward one or the other. I would say this is mostly a matter of taste and much less so of quality. What is a matter of quality however are resolution and transparency. The Mola-Molas are simply more finely resolving and transparent. This is most evident in the treble, which with the Mola-Molas (as well as with Jeff Rowland and Ayre) is more fluid and airy, but without adding any smear.

So, whilst better performance can be obtained, you’d have to spend at least 10k to achieve this. It’s always the last few percent that cost the most to achieve! Nonetheless, the NuPrime just performs admirably even in the context of super high end speakers and that really is quite remarkable.

Above: NuPrime amidst of some of the finest power amps available. In the back row: Analog Domain M75P, Mola-Mola Kaluga, Bryston 3B Cubed and 14B Cubed. In the front row: Mola-Mola Makua (which is a preamp), PrimaLuna DiaLogue Premium and Jeff Rowland 625 s2.

Conclusion

I’ve heard many class D amps, but have liked very few. While bass control and neutrality are often a piece of cake for these amps, they are usually let down by thinness, harmonic deficiences and an unnatural timbre. The NuPrime ST-10 is the first class D design that sounds timbrally wholly convincing to me. Piano really sounds like piano, not like synthesizer and vocals are just as direct-coupled as they are in real life. Add in bass heft and thundering dynamics like I have not yet heard from other class D designs. Only the Mola-Mola Kalugas ultimately provide more refinement and transparency but these are placed at the complete opposite price spectrum.

On balance, there is just no denying that at any price the ST-10 is an exceptional amp. Heck, at a mere 1595 euro, it is simply sublime! NuPrime are not exaggerating when they say that they have implemented both solid state and tube elements into the sound. Just don’t expect the ST-10 to sound like a generic romantic and mushy tube amp but rather more like a lightning fast SET with ultra clean, clear midrange. Like a good SET, the ST-10 does not add warmth or romantic colourations but produces pure, honest and lively music, complete with the highly lyrical qualities that come along with this type of amp.

Finally, NuPrime believe that the customer should be able to choose from a palette of amps with different characteristics, to match personal taste. So, should all this talk about purity and powerful dynamics put you off and you’d prefer a more creamy-rich sounding amp, then NuPrime has alternative solutions for that such as the the MCH-K38 or STA-9. In any event the ST-10 is my new class D reference in its price category, and way above it.