– John Ransley, totallywired.nz

This is NuPrime at their very best –  the new STA-100 is their most affordable power amp yet, a radical internal design and fantastic sound quality that will have you wondering how such a small box can produce such a big sound.

Complexity is the enemy when it comes to sound quality. The more bits you have to put the musical signal through, the longer the signal path, the more chance there is to get it wrong – you loose information and quality while adding distortion and noise. Sure you can try to engineer out these problems with costly components and endless iterations of design but why do things the hard way? By the time you do will anyone even be able to afford it?

Electrical inefficiency is just as bad. Almost all amplifiers generate appreciable amounts of heat as part of their design. So they need heat sinking and have to be big enough to accommodate both this and the extra power supply that’s often doing little more than heating your room. Let’s not even think about the accelerated ageing of the internal parts when they are hot.

So you can understand that there is a theoretical ideal of an amplifier that is both very simple and efficient in it’s design. But what we haven’t yet considered is power – specifically the output power that makes your speakers go. In the real world you need quite a lot if you want to have fun and make the most of even quite modest speakers. And most modern speakers are actually very capable in both their power handling and their potential to sound really good.

Enter NuPrime’s newest and physically smallest power amplifier – the STA-100. Yes –  it’s a genuinely 100 watt per channel amplifier (into 8 ohms and 150 watts into 4 ohms). But what the website pictures don’t show you is just how small it is; just 15.1 cm wide 13.6 cm deep and barely 5 cm in height (including the feet even). At just 1.8 kg it still manages to feel quite chunky.

NuPrime STA-100 stereo power amplifier

This is undoubtedly a quality package – the box it comes in is a rather lovely design, the unit itself is very well finished with solid, gold plated connections and some interesting switching and set up options.

We’ve known the STA-100 has been in the pipeline for a while and have been able to form an idea of how it was likely to sound. But as always, preconceptions should be put to one side and it’s what we actually hear that matters.

This amplifier is nothing short of revolutionary. While NuPrime have been producing ever more sophisticated versions of their hybrid class A/D amplifiers at the upper end of their range, this design excites me because it gets to the heart of music, in a way that just has not been possible at this price level and is a ton of fun to boot.

By stripping the concept of a Class D power amplifier back to the essentials and coupling a new switched mode power supply design, NuPrime have come up with something that’s undeniably special.

You can hear this immediately – there’s simply stuff going on in the music that you will have never heard before. And it sounds big – not just the old ‘sound’s bigger than it looks’ thing, but seriously impressive even from the outset. I’ve heard plenty of much more expensive and supposedly powerful amplifiers that really should be hanging their heads in shame right now.

The STA-100 is real high end – it’s expressive and detailed, pacy and involving. And when NuPrime describe it as having ‘explosive power at high volume’, they aren’t  kidding; this baby can go!

And it just gets better as it warms up. 

This amp goes when you need it to but is also very well behaved. The background noise levels are vanishingly low. The STA-100 is really good in this regard and we can put our ears right up to the speaker when it’s on and there’s effectively nothing. The actual specification is -90dB; on par with the new NuPrime STA-9X which is twice the price and has a more conventional toroidal transformer based linear power supply.


And it’s the power supply that’s the beating heart of this unique amplifier. The ‘Adaptive Voltage Switching Power Supply’ is an electrical turbocharger. Just like a turbocharger on a small car engine delivers a big jump in power yet still has great fuel economy. Almost every other amplifier out there separates the power supply from the musical signal and passively draws upon that power to work. The STA-100 has a cleverly designed loop that senses the incoming musical signal and then steps the power supply up as required to amplify it. And you can really hear how this works.

At low levels you don’t need much power and so it’s just doing what it needs to do. That’s why it’s so quiet and allows more detail through. And why it runs so cool and can be so small.

But the moment it senses a rise in the incoming signal it steps up – and this is where NuPrime’s experience with both Class D and switched mode power supplies makes such a difference; the very high switching speeds – 550 to 600kHz means that there is no audible lag. In fact the STA-100 sounds definitively pacy and fast. It’s literally straining on the leash at times when you feed it challenging and exiting music. And just as quickly as it steps up it can drop straight back down to an eerie silence when the recording demands it. Agile is the word.

Too many amplifier designers overthink their circuits, often to compensate for legacy components or a particular topology that has come do define a brand (think MOSfets.) With the STA-100, NuPrime have clearly gone the other way, stripping the design back to essentials and adhering to the ‘Less is More’ dictum. Again, you’ll immediately hear that this approach lets more through and gets to the heart of a performance. 

There are some serious Tube audio designers out there that have also gone down this path, with very simple designs based around a small number of premium tubes and components. But the big issue with these is the low power. While we aren’t suggesting the NuPrime is a direct replacement for an esoteric 12 watt SET amp carefully matched with some extremely efficient and costly speakers, what you get with the STA-100 is an equally innovative approach that works with real world speakers and offers something really special for a fraction of the cost. It’s just so much fun and will put a real smile on your face.

Being a power amplifier, you’ll be aware that the STA-100 needs either a preamplifier or a source with a volume control to work. There’s a very good rationale behind the concept of a separate power amplifier – it’s designed to exactly fulfill it’s purpose with no compromise. You gain great flexibility in that the better the preamplifier or source you feed in to it, the better the sound you’ll get out. And often you can take a progressive building block approach and improve your system over time and even add another STA-100 (we’ll cover this in more detail shortly)

NuPrime STA-100 stereo power amplifier
The NuPrime STA-100 rear panel


The Nuprime STA-100 has an unusual and very useful set of features for a power amplifier making it the best choice for an impressively wide range of systems. The Gain Switch on the rear panel being the most useful. What this does is allow you to perfectly match the STA-100 to almost any source and speakers. There are 3 settings – 15x, 20x and 30x. What this means is that the STA-100 amplifies the incoming signal by that much. This is great because there is a really wide variation out there in source component output and speaker sensitivity. It makes a big difference to the apparent power of the amplifier through greater dynamics and punch.

There is a 5v USB power supply slot – obviously you can never have enough smartphone charging points but this will prove useful for the increasing number of source components that use 5v as it takes over from the old 12v standard. Speaking of which there are also two 12v trigger sockets – in and out – which enable the ST-100 to be remotely switched on out of standby and off when not in use as well as daisy changing to other such components. This is especially useful in surround sound and multi-room environments.

The front panel has two tiny LEDs  – the first one indicates either standby or on states. The second you should see much less often – it glows yellow if the overload protection is activated. And because it does have this we’d hope you’d never see the red fault light. As it stands I’ve given the STA-100 some significantly hard runs and have yet to see the yellow even start to flash.

The small size and the low price of the STA-100 means there are some things you’ll have to go up the NuPrime range to get. Balanced inputs being one but it’s hardly an issue at this price level and quite simply there is no room on the back panel anyway. The ability to bridge is another feature found in the more costly models but you can still bi-amp and there may just be a mono version in the pipeline so it’s hardly a game breaker. The STA-100 never feels like a compromise.

Gaining perspective.

At it’s price level, the STA-100 is remarkable and it feels churlish to suggest it could be better when it’s obvious that to make any worthwhile improvements would significantly increase the price. When I first listened to it, the power cable, interconnects and speaker cables all (individually) cost more than the actual amplifier. And it was replacing a considerably more costly unit. Yet it never felt like it was holding the system back. In fact this allowed the STA-100’s character to shine through; vivid and lucid, exciting and yet surprisingly subtle. 

The simplicity of the circuitry makes itself heard in the transparency of this amplifier – you really do get an expanded and amplified version of what you put in. And that really is the job of a power amplifier. Could it be better? I’m not so sure that doing a higher power version would be a good thing – the added complexity, increased parts count greater potential compromise made by internal EMF could take you backwards – and in any case it would cost more to build. Better internal parts would again just add to cost and as we have found, when it’s possible to achieve the same result with carefully chosen cables, you can reach the same point anyway.

NuPrime are at the point where they can intentionally ‘voice’ any of their amplifiers to sound as they want. The STA-100 is very on-brand with a clear vocal presence and sound that I describe as ‘live’. If you read our review of the more powerful NuPrime MCX-2 you’ll get a feeling for this. A cinematic metaphor for the STA-100 sound is ‘Technicolour’. It’s just the thing to brighten up your day!

The foil for this is the NuPrime AMG STA; this is what it takes to go beyond the STA-100 in terms of subtle textures and shadings. Yet still I can hear a little of the AMG’s fluidity informing the performance of the STA-100 especially at lower levels. 


The ST-100 hasn’t come out on nowhere – it’s a unique amplifier that could only have been designed by NuPrime and is the product of many years of R&D. 

Let’s go right back to 2005 and a review of the NuForce Reference 8B mono power amplifiers. The transition to ‘NuPrime’ was still a decade away but already the building blocks are there with a seriously high end 100 watt per channel Class D power amplifier operating on a switched mode power supply. In 2008 the first NuForce that we’d get to hear emerged – the ultra compact Icon series.

These amplifiers marked a turning point for Totally Wired. The NuForce Icon became a series of models – all tiny yet unfailingly popular, reliable and definitely outperforming anything else for the price. We’ve never looked back.

By 2013 we had the the NuForce STA-100 (NZ$1099 at the time). Same model number and same rated output but dig a little deeper and there are significant differences, which make the new STA-100 even more remarkable. Having had a lot of time with both versions and the benefit of listening to numerous other NuPrime models over the intervening decade, I can tell you there’s been real forward progress made in terms of sound quality. The new STA-100 operates at a significantly higher switching rate but it’s the power supply where the greatest changes appear to have been made. Good as the original was, the new version sounds vastly better – more powerful and dynamic, far more detailed and involving. Factor in the changes in exchange rate and inflation and the new NuPrime STA-100 is even better in terms of value.

When you read some of the old reviews there had been a thing with putting the NuForce and NuPrime amps with some wildly costly and demanding systems in order to find out just what they are capable of. We found the STA-100 more than capable of not just driving Sonus faber’s stunning Olympica Nova II floor standers yet actually sounding very good while doing it. The transparency of these speakers is going to reveal the innate character of anything further up the chain and we were quite honestly taken aback by just how well the STA-100 performed. In fact all it really made us think was how good two of them would have been!

But this really misses the point of who is most likely to really appreciate the NuPrime STA100 – it’s the music lovers that would normally struggle to afford separates or assume that they have to buy secondhand to get a shot at high end sound. The first unit we sold went into a small system with a 40 watt Rotel Integrated amplifier that was running well but maybe just missing something. Connected via the Rotel’s preamp outputs the STA-100 bought the system to life and has proved to be a real hit. On the Saturday night we got a txt – ‘Omg. My system just found a friend lol.’ Sometimes these snippets are the best reviews 😀

So how will the NuPrime STA-100 fit into your system? Many integrated amplifiers and almost all AVRs (Surround sound receivers) have pre-out sockets. Most of these will have lack both the sound quality and actual actual power of the NuPrime. So there is an immediate improvement. But there’s another important benefit; because your existing amplifier is no longer struggling to drive speakers (or the most demanding front speakers in the case of surround sound) it’s suddenly got power to spare which greatly improves the performance of the internal preamp section. Which in turn feeds an even better signal into the NuPrime.

For anyone with a separate pre/power combination, the NuPrime STA-100 can be a real eye opener. We’ve all been conditioned to equate large and often costly with good, but if you want to try an STA-100 it’s easy as  – the box literally fits in a $12 courier bag and the actual amp will fit anywhere. What have you got to lose?

In a new system the NuPrime opens up a whole raft off possibilities. Because it’s delivering an unprecedented level of performance for the price, and costs so little, you can look at better sources and speakers than might have otherwise been possible.

Within NuPrime’s own range there the new WR-2 streamer is an obvious starting point given it’s similar form and cost.  But you could also aim  higher with the the NuPrime ‘9’ series DAC or analogue preamp and have a wicked combination.

Looking even further to other brands, we’ve already found that the class leading Lumin network players all match very well with NuPrime; with any of these, the STA-100 allows you to enjoy a level of performance that you simply won’t be able to get without spending considerably more. 

And with speakers, while it’s early days yet in terms of hearing the STA-100 with a broad variety of brands and models, everything we have heard suggests this amplifier will work both safely and well with a broad range, irrespective of price or rating. The gain switching feature means that it’s possible to match the NuPrime with many more systems than would have otherwise been possible. And if you make changes in the future, the STA-100 will be well placed to not just accommodate but actively optimise the improvements on both sound quality and quantity.

I’m struggling to find a downside. In fact the only one will be for us in that people may be so happy with the entry level to NuPrimes’ range that they choose not to look further up the food chain to the even better models; But more importantly this model is a welcome addition and delivers an authentic NuPrime experience to a whole new audience.

Link to the review --> https://totallywired.nz/nuprime-2/nuprime-sta-100/