NuPrime ST-10M ST-10Ms mono power amplifier in black at Totally Wired

NuPrime new ST-10M mono power amplifier NZ$2850 each

The new Nuprime ST-10Ms mono power amplifiers incorporate a series of internal improvements which allow the design to work at a much higher level. The refinement of Class D operation with both better electrical efficiency and much lower cost of construction means they simply deliver more for less. If you are after both a big, rich, room filling sound and still want detail, speed and control, the new ST-10Ms are made for you. The new ST10M story starts with the well proven ST-10 stereo power amplifier – NuPrime’s best single box stereo power amplifier. Compact and cool running, it is also remarkably powerful with a conservative 150 watt per channel rating. Compared to other highly regarded amplifiers the NuPrime is very affordable. But most importantly it sounds great.

Since it’s introduction in 2015 we’ve placed the NuPrime ST-10 in many client systems with universally positive results – you can read our take on the ST-10 here.

This has been reinforced by other reviewers’ findings – often in the context of wildly esoteric systems –

‘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….In any event the ST-10 is my new class D reference in its price category, and way above it.’ HiFi Advice.

‘The NuPrime, by comparison, is a truly tiny amp. And being extremely affordable, if I did not know better then it would be easy to assume that it would be under qualified for any Wilson. The truth could not be more different: the ST-10 really brings the Sabrinas to life! Where all other transistor amps seemed dynamically a little restrained and only the PrimaLuna provided the kind of subjective dynamic swing that I crave, the NuPrime ST-10 has a kind of energetic presence that none of the other amps (transistor and tube) could match. Transient crispness and dynamic impact are really startling, better than with any of the other amps. Bass with the ST-10 is also incredible, not in a big and fat kind of way, but tuneful and articulate with just the right amount of pressure. Meanwhile, the NuPrime’s very pure tonality and open and communicative character further increase the Sabrina’s timbral believability.’ HiFi Advice – Wilson Sabrina Review.

‘I was especially impressed by the ST-10’s performance at the top and bottom of its range. The bass was taut and tuneful. Conversely, the upper midrange and treble were airy yet accurate. On recordings with exaggerated upper midrange or treble energy I was aware of the additional musical information, but it was never emphasised to the point of harshness. After living with the ST-10 for a while I can understand why NuPrime draws attention in its sales literature to the ST-10’s “tube-like” upper-frequency characteristics. While the ST-10 certainly doesn’t soften or roll those off in the manner of classic tube designs, it brings to its upper frequencies the kind of ease and sweetness that are usually found in power amplifiers that employ tubes somewhere in their circuitry.’ The Absolute Sound.

The recent introduction of NuPrime’s new flagship reference power amplifiers – the Evolution Ones – show just what NuPrime are capable of when the constraints of size and budget are extended.  The new ST-10M (Mono) option draws upon both the proven ST-10 design and the Evolution One design process.

Smart Design.

On a simplistic level, the ST-10M is a much more powerful unit while maintaining much of the inherent goodness of the ST-10 design. But given the development of the Evolution Ones and the time since the introduction of the original, you’ll understand that there is rather more going on inside.

Let’s dig a little deeper.

The ST-10M is rated at 230W @ 8 Ohms and leaps up to 320W @ 4 Ohms. This is a significant departure from the stereo ST-10 which has an output of 150 watts regardless of speaker impedance. The ST-10Ms have an improved power supply which makes this possible and make this option much better for both more demanding speakers and larger rooms.

The internal pictures provided from NuPrime clearly show how they have done this. The stereo ST10 has two discrete boards for the left and right hand channels. The ST10M uses a single one of these boards and adds extra power supply components to fill the space – a dual bank of capacitors being the most obvious.

Nuprime ST10 internals.jpg
ST-10M on the left, the original stereo ST10 on the right.

I’ll admit the internals can look a little less pretty than a single PCB layout – but there are advantages in having several discrete boards to deal with the different amplifier sections – power supply, storage, and the actual amplifier. Some are existing modules which saves on cost. The actual assembly (and any possible servicing) becomes quite simple. And physical isolation of parts can help reduce noise and interference.

The input impedance has also increased by a similar factor from 23.5k Ohms to 47k. The value of doing this is amply illustrated in the stellar performance of the Evolution Ones which work at higher impedance levels again.

To really bring out the best of the V4 amplifier module, the ST-10M has a new 300W power supply for its mono channel.

The original 10A bridge rectifier has been replaced by a 50A Schottky diode, the capacitors upgraded 30,000 micro-Farad, and the power transformer is now rated at 300W. Improved circuit layout with careful component selection has allowed the ST-10M to have a lower noise floor than the ST-10.

And needless to say the complete physical separation of the two channels gives a level of isolation just not possible in a single box design.

NuPrime ST-10 back panel.png
NuPrime ST-10M back panel – Eichmann Cable Pods, Rhodium plated RCA and Balanced input.

On the back panel you’ll see a set of Keith Eichmann’s ‘Cable Pod’ speaker binding posts – the contribution these make to the end sound quality should not be underestimated. Likewise the RCA socket (exactly the same as that used in the Evolution Ones) and balanced input.

Combine all these improvements and you’ll be able to understand that the ST-10Ms are a major step up from the original stereo version. This is why the new models are designated ‘Reference’ whereas the stereo was ‘Reference LE’.

Yet the effective price per box remains the same – in part it’s a smart move by NuPrime to use the same casework. And it’s a nice little nod to one of the models that NuPrime’s reputation is built on – the similarly proportioned NuForce Reference 9s.

‘Frankly, the NuForce Reference 9s do so many things right that I hardly know where to start, but let’s begin with the two qualities that grip most listeners first: resolution and transparency. The Ref 9s offer a truly extraordinary level of see-through transparency, and as an audiophile friend so aptly put it, “Their transparency is real, not a fake artifact caused by brightness.” That brings me to a second revelation: These little amplifiers not only deliver gobs of musically relevant detail, but do so without imposing the fingernails-on-a-chalkboard torture of excess brightness. In this respect, the Reference 9s combine some of the whole-cloth sonic integrity of the mighty MBL 9011s as well as a good bit of the focusgoes- on-forever clarity of the ASR Emitter II. How does this play out in musical terms? Well, for me it means falling in love with the timbres of individual instruments and voices all over again.

As I write this, for example, I’m listening to the Quartetto Italiano perform the Dvorzak “American” String Quartet in F Major, Op. 96 [Philips, LP] savoring the way the NuForces reveal the profoundly complex voices of each individual instrument, as well as the interplay of those voices as they meld to form a greater whole (and isn’t that the real magic of great string quartets?). Similarly, on good live recordings, such as Eva Cassidy’s Live at Blues Alley [Blix Street Records], the NuForce’s bring my system alive with the sort of crackling, electric intensity you typically experience only in live music venues—an intensity heightened by the amplifier’s ability to capture, simultaneously, the delicacy of Cassidy’s voice, the scorching heat of electric guitar solos, and the giant-hearted punch of the electric bass. The word picture I’m hoping to paint, here, is one of an amplifier that essentially never sounds congested, regardless of the complexity of the material being played (a quality the the ASR exhibits to an even greater degree).

Next, as a bassist, I feel compelled to point out that the NuForces deliver the best doggone bass-pitch definition and control I’ve ever heard from any amplifier. Part of what’s going on is that the NuForces offer a damping factor greater than 4000 (no, that’s not a typo), so that when the Ref 9s tell woofers what to do, the drivers have little choice but to shut up and follow orders—precisely. The sonic results can be eyepopping in several ways. First, the Ref 9s seem to give some speakers (e.g., my Magnepans) about an extra half octave of bass extension they never had before. Second, the amps draw out layer upon layer of bass textures and detail you may never have heard before. A few nights back I put on master acoustic bassist Dave Holland’s Emerald Tears [ECM, LP] and listened in shocked amazement as the NuForces revealed one new subtlety after another (the intricacy of Holland’s solo work is just unbelievable!). The only word of caution I would offer is that the NuForces handle low frequencies with the utmost control, and therefore will not artificially “warm up” either recordings or loudspeakers that lack bass. But put these amps together with recordings and associated gear that can do bass well and it’s “fasten your seatbelts” time. hifiplus 2008

If this review paints a compelling picture just think about how much better again the ST-10Ms are – almost twice the power and 10 years of development go a long way.

In fact if you dig into the immediate history of the NuPrime and NuForce ranges, it’s the Reference 20 that is the closest to the new ST-10M – both use the same V4 module, both are mono amplifiers. This also illustrates that the team behind these designs have built quite body of experience over time and any reservations we might have harboured over the sound and performance of Class D or switching amplifiers have been addressed.

‘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 amplifier design page.

One important matter that I want to 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.’

I’ll also address another point of difference with the NuPrime amplifiers – while NuForce models employed Switch Mode Power Supplies, the NuPrimes feature toroids. The SMPS units did offer great output levels for low cost and high efficiency but there was a downside with noise levels and occasional reliability issues.

That said, they are also much quieter than the toroids used in conventional amplifiers and the reason for this is the much higher electrical and thermal efficiency of Class D over the conventional Class A and AB approaches.

And this gets to the heart of why NuPrime are so much better –

If you look at any of the ‘big’ amplifiers, in order to produce enough power to really drive speakers, the designers had no choice but to push in massively oversized power supplies and copious heat-sinking – you get hums and noise, you get heat and attendant shortened lifespans of capacitors. The high voltages and currents demand brute force solutions. This costs dearly – not only in the dollars but also to the integrity of music. I’m as guilty as anyone of being impressed by the size of such products which inspire an almost macho mindset – but really – we’re trying to reproduce music here – not comparing forearm development.

What can you expect to hear with the ST-10Ms? Here’s a review to supplement what we’ll describe below. You can also reasonably extrapolate from both the many ST-10 reviews and experience of what happens with other similar products within both the NuPrime range and beyond.

Within the NuPrime range we can point to the smaller STA-9 which can be bridged. In it’s stereo configuration, the STA-9 puts 120 watts into each channel and sounds both sweet and solid. You can add a second STA-9 to your system, flick the back panel switch to bridged operation and suddenly have a pair of 290 watt mono amplifiers. The sound is suddenly ‘bigger’ – this is not only about going louder (which they most certainly do). Greater available power improves dynamics – the difference between the quiet and loud bits within music which makes for a more ‘live’ and involving sound. The soundstage – the illusion of instruments and performers being located in a space between, and sometimes outside the speakers, is where the most striking improvement often takes place. The performance space becomes more expansive, often to the point of being immersive. In a word it is more real – and this is why we get enthused about sound quality. One STA-9 is good. Two STA-9s are precisely twice as good and are very nearly at the level of the ST-10 (stereo) in terms of absolute performance.

Yet with the new ST-10M we are looking at a greater improvement. Remember that the bridged STA-9s are internally identical to the single stereo STA-9, we have only changed the configuration. The new ST-10M incorporates a series of internal improvements which allow the design to work at a much higher level. Bridging can also have a downside in that it can make an amplifier less tolerant of low speaker impedance – I’ll reiterate that the ST-10M is not a bridged amplifier and so its performance with difficult loads is even better than the original stereo version.

If you are after both a big, rich, room filling sound and still want detail, speed and control, the new ST-10Ms are made for you. Add in completely silent operation, a scarily low noise floor and cool running and you’ll see why other designers are taking notice.

By the numbers…

  • Power Output (rated): 230W @ 8 Ohms, 320W @ 4 Ohms
  • Power Output (peak): 270W @ 8 Ohms, 375W @ 4 Ohms
  • Gain: x 28
  • Input Impedance: 47000 Ohms
  • Sensitivity: 1.5Vrms to rated power
  • Total Harmonic Distortion (THD): 0.01%
  • Signal to Noise Ratio (SNR): 91dB @ 10W
  • Frequency Response: 0Hz to 50kHz (-3dB)
  • Standby Power Consumption: 0.9W at 115V outlet, 1.7W at 230V outlet
  • Idle Power Consumption: 14W at 115V outlet, 14.8W at 230V outlet.
  • NZ$2850 each – $5700 the pair including GST and delivery – Black or silver finish.

Given all of the above, what amplifiers do the NuPrime ST10Ms stand direct comparison with? The highly regarded Mola Mola Kalugas at US$16,500 the pair are our starting point – they have been out for a couple of years, are also a compact cool running Class D design. While I don’t suggest anyone is likely to trade in their Mola Mola for a NuPrime at 1/5th of the price I am saying that they will get you to the same performance ball-park.

In the first linked reviews at the top of the page there are many direct comparisons of the stereo ST-10 to the likes of PrimaLuna, Bryston, Ayre, Audio Research and Jeff Roland. The improvements made with the NuPrime Monos are so significant that these comparisons will need to be revised.

Maybe it’s the small size or relatively low cost of the ST-10 that means some don’t take this amplifier seriously – the reality is that the ST10Ms sound far better than many much bigger and more costly designs. As much as I have supported NZ made in the past it has become obvious to me that both Plinius and Perreaux have stalled. Only Pure Audio remains as a credible force – Gary Morrison and Ross Stevens’ approach to electronic and product design is unmatched in New Zealand and they have a deservedly solid reputation overseas. It is impossible to fault the quality of construction, parts selection and layout.

But the NuPrime approach is, to my ears, yielding better results with power amplifiers. The refinement of Class D operation with both better electrical efficiency and much lower cost of construction means they simply deliver more for less. The quality of sound, abundance of real power, ease of set up and use due to cool running are compelling advantages for NuPrime.


Most NuPrime ST-10Ms are likely to go into existing systems as an upgrade for another power amplifier. The benign input impedance, standard input sensitivity, connections and small physical size all stand in their favour, so matching existing preamplifiers and speakers is straight forward. Demanding and low impedance speaker systems that may have pushed the stereo ST-10 will be a breeze for the monos.

If matching to new components, I’ve got a few ideas you might like to consider. Obviously NuPrime’s well proven DAC-10 is both an aesthetic match in the same sized box with both digital and analogue sections well covered.

The Evolution DAC delivers far better performance on the digital front – the performance gain is every bit as much if not more than the difference between the ST10 stereo and the ST 10 mono.

But the best of all is the new NuPrime AMG PRA analogue preamplifier – assuming you have your source components sorted – ie a decent analogue front end or DAC, the AMG PRA lifts performance to a stellar level and shows you everything the power amps can deliver.

On the speaker front, the power of the ST-10Ms will make it a hit with many larger speakers – I haven’t had a enough time to experiment with many combinations and in part, I’ve been waiting for the new Sonus faber Sonetto range to see what we can do with floor standers. That said, my experience with the stand mount Monitor Audio Studios combined with NuPrime’s flagship Evolution One monos suggest that these might be a great foil for the ST-10Ms – the Evolutions are almost too much for the Studios and make their laser like projection just a bit overwhelming – the more compact ST10M monos should be a bit more relaxed but also add greater depth and extension compared to the stereo ST10.

I’m also going to give a shout out to Shahinian owners – as a long time fan of these speakers we always felt that most amplifiers never did them justice – the new ST-10Ms seem to be made with these speakers in mind – there’s all the power they need, serious bass extension and control.

NuPrime new ST-10M mono power amplifier NZ$2850 each

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