The NuPrime MCH-K38 8 channel power amplifier NZ$4500.

All about the NuPrime MCH-K38 8 Channel Power Amplifier.

8 Channels, with both RCA and balanced inputs, bridgeable in any combination to 400 watts each.

Not only is this by far our best and most exciting surround sound amplifier – the NuPrime MCH-K38 is to all intents and purposes our very best and most powerful stereo power amplifier – with a couple of very interesting twists. While we have been concentrating on the launch of the highly affordable NuPrime 9 component series in the last few months we’ve had the new MCH-K38 8 channel power amplifier bubbling away in the background.

The NuForce 8 channel models were a bit of a hit with us – simple, powerful and surprisingly good sounding, especially in the context of the price. They provided a great antidote to AVR mass market where single box receivers get ever more complex, compromised and often intimidating.

NuPrime is a new company and while there are some common design elements, the reality is that this is a fundamentally different and much better product. The NuPrime aims higher than just being an alternative – it’s designed from the ground up to be one of the very best power amplifiers you can own of any breed or description. The trick is in finding out how it will works best for you.

To help you understand why the ‘K38 works as it does, I’m going to take you through a few key technologies and hopefully explain why it can sound as good as it does.

There is a unique design to the heart of all NuPrime amplifiers. Unlike traditional Class A or AB which are based around a large transformer ticking (or often buzzing) away at 50hz, the NuPrime is a self-resonant design operating at a far higher (and hence much faster) frequency. The MCH-K38’s 550 kHz PWM switching frequency constantly adjusts to the input signal, output current demands, and loudspeaker impedance variations.

Just think about these numbers for a start – the NuPrime is operating at a level 11,000 times above that of most other amplifiers. It is radically different. This starts to explain how the NuPrime can be so compact yet deliver 8 x 210 watts in a box the size of most power amplifiers that might be lucky to produce 2 x 100.

Going into more detail, the MCH-K38 amplifier is derived from the ULCAM (Ultra Linear Class A Module)+Class D design first introduced in IDA-8. By joining a powerful high impedance single-ended amplifier circuit in the preamp stage with a well integrated Class-D power stage, you effectively get the best of both worlds. The warmth and resolution of Class A is applied at the start, but because we’re not asking this part to drive speakers, there is no downside in terms of excess heat and power consumption.

While NuPrime describe the MCH-K38 as having a rich tube-like sound, there is no way an all tube design can compete in terms of power. And as we’ve previously intimated, the NuPrime design is fast and responsive.

Where the ‘K38 multichannel differs from both the stereo STA-9 and ST-10  power amplifiers is that it has no toroid as a primary power supply – because of the massive amount of output power demanded, a 1000W power supply and CMA capacitor array is employed.

The idea of ‘Class D’ is gaining traction with many designers as a route to more power at lower cost – the downside is that in order to keep the price down, the switching frequency is much lower than that employed by NuPrime – and the harmonics of this bleed into and damage the musical signal – so you might hear that so called ‘digital’ amplifiers are often hard sounding and perform poorly in the bass.

So let’s get back to the quality. The MCH-K38 is stated to be a Reference LE class multi-channel amplifier designed for uncompromising home theatre and music listening. From our own listening, it’s obvious that the ‘K38 is working at a level well above the STA-9. But what is more significant is that it is also able to better the best of the dedicated stereo power amplifiers, the ST-10.

On one hand, the ST-10 still has some advantages in that it runs at an even higher frequency of 600 kHz. And although rated at 150 watts (the ‘K38 at 210), my feeling is that with just two channels driven, the ST-10 still comes out slightly ahead. But the ‘K38 has 8 channels so is not far short of being 4 ST-10s in a single case for less than 2x the cost.

Let’s consider bandwidth. This is the frequency range over which an amplifier reproduces music. Our hearing is nominally 20 Hz to 20,000 Hz and this really should be considered bare minimum but a lot of amps are specified to this level and no more. The MCH-K38 delivers a flat response over the range of 10Hz to 50kHz. Which means phenomenal bass control and an unusually airy treble with lightening fast transients.

Bridging

Now we can look at what happens when we bridge. This is simply combining two channels into one which gives a dramatic increase in power. What isn’t so simple is how this works with different designs and if there is a trade off between quantity and quality.

Not that many amplifiers can be bridged – the reason is that with conventional designs, while bridging can give 2-3 times more rated power, it also gives higher distortion levels and lowers the ability of the amplifier to deal with the low (4 ohm) impedance loads presented by a good proportion of speakers. Bridging a conventional amp lowers the effective impedance and amplifier ‘sees’ in a speaker, so an 8 ohm speaker presents a load similar to a 4 ohm speaker when bridged. It follows that a 4 ohm speaker presents a 2 ohm load and this is starting to get too close to a short circuit which inevitably leads to big problems.

As you already know, the NuPrime design is not conventional. The MCH-K38 has a stable output into differing loads – 8 ohms or 4, it is rated at 210 watts per channel. When bridged it maintains this stability and ramps up to 400 watts per channel – again into either load.

What is unusual, is that NuPrime specify that the rated distortion actually drops when bridged. It is precisely halved. Now I don’t know enough to say why this happens and I’ve got no reason to disbelieve NuPrime – given the unconventional nature of the design, the claim is plausible and in practice the sonic results I hear back this up.

The improvement made by bridging is immediate, substantial and transformational. In this mode, the K38 far outperforms the ST-10. The sound produced is much more open and dynamic but also smoother and more musical. With lesser amplifiers, bridging results in a more aggressive sound but with the MCH-K38, it’s just better in every regard.

On this alone, the NuPrime MCH-K38 is an exceptional wee beast. Given the NuPrime ST-10 already a reference standard, to get quality that exceeds this AND delivers 400 watts on tap should be getting your attention.

Remember that the ‘K38 has 8 channels in total. So if we bridge 4 of them into two to drive a single pair of speakers, there are still 4 unused.

 

In a 5.1 cinema system that means you can also bridge another pair for the centre speaker and still have 200 watts each for the surrounds. Are we having fun yet?

What if we want to take stereo to the extreme and really see what a full range set of speakers can do? Most serous speakers have dual terminals for bi-wiring. Which also means bi-amping. So with the MCH-K38 you can bridge all pairs giving you 800 watts into each side evenly split between the upper and lower sections. Will you even be able to use all of this?

Power is not about loudness (even though there will be as much as you could ever want). What 800 watts a side buys you is unparalleled headroom and dynamics. It’s like opening a window – in this case a very big one – to your music. The very quiet bits are still quiet but you’ll pick up fine detail that was previously obscured. As the levels climb, the clarity is maintained without stress or strain. Your speakers will exhibit control and definition like never before.

So what speakers would we match the NuPrime MCH-K38 up to? Monitor Audio’s new Platinum 2 flagship range will allow you to hear this at its very best – the uniquely wide bandwidth stretching up to 100kHz that the Monitor Audio ribbon tweeter delivers makes the most of the speed and extension of this amp and there are no problems at all in terms of power handling. All of the models from the stand mount PL-100-II right up to the massive PL-500 floor standers will just sing.

Likewise the new Gold series offers a more affordable combination – still with a remarkable ribbon transducer that makes complete sense with this amplifier. On the Italian front, the new Chameleon T floor standers. really appreciate the solidity and control that the K38 delivers in the bass. As a combination, this is a remarkably affordable way to fill a very large space with and easy listening and unusually smooth sound.

What NuPrime are doing here is quite possibly unique. There are very few amps of any breed that deliver this kind of power, let alone in this configuration. Add to this the comparatively low cost, compactness, cool running and you have a veritable giant killer.

In the past we used to have to look to locally made brands when muscularity was required. But they came with all sorts of issues and in hindsight, impressive as large handles and heatsinks looked, they may not have been on the right track. I know this from personal experience.

While the power is pretty exciting to talk about, what we all really enjoy listening to is quality and I don’t want you to lose sight of what NuPrime do in this regard. The first time I ever heard a NuForce product (the diminutive little Icon amp) it was the sound quality that made an immediate impression. NuForce – and now NuPrime – produce a sound that manages to blend the best of all worlds – first and foremost, the midrange where vocals are most instruments reside is always spot on – rich yet detailed and always natural. As we go further up the NuPrime food chain it’s the frequency extremes that become enhanced – better more solid bass and one end and more open, faster and defined treble at the other. In all cases there is a remarkably quiet background where music just seems to hang. The natural decay of notes is a particular strong point.

As we go in a series of steps from the little IDA-8 integrated, through the 9 series options and up to the Reference LE series products, the sound staging becomes more expansive and defined. It reaches a peak with the new MCH-K38 in full bridged and bi-amplified mode.

Given the capabilities of the ‘K38 I’ve put a lot of thought into how we best exploit it but also maintain the remarkable value for money it represents.

In a Home Cinema setting, my first recommendation is to team it with Cambridge Audio’s brilliant new CXU Blueray player – this is far more than a universal disc player, having seriously good preamp section with multiple digital inputs and multi-channel analogue outputs allowing you to directly connect and control the NuPrime MCH K38.

The Oppo players (103 and 105 in their various guises) are the next best thing along with the previous Cambridge player, the highly regarded 752-BD. In all cases they will give you fantastic playback of both movies and music discs.

On a quick technical detail it’s worth knowing that the MCH-K38 has an input impedance of 47k ohms – this means it’s an ideal match with all of these players

In a purely music playing stereo system there are more permutations, especially when looking to make the most of all the the available 8 channels.

But first – another useful wee trick. The front panel of the ‘K38 has switching for all of the channels. If not using any of the 8, then they can be switched off which effectively diverts the available power supply to the others.

As we’ve already shown you, the ultimate configuration for a pair of stereo speakers is the bridge all pairs and run in bi-amped mode. This will require two sets of speaker cables and likewise for interconnects. While the ‘K38 features both balanced and RCA inputs, my own listening suggests that its not which type of connection you use that makes the difference but the quality of the actual connecting cable. How far you go is entirely up to you but I’ve had some pretty fantastic results for both myself and a good number of clients with the new KLEI range.

Depending on your music sources there are some excellent choices from NuPrime in terms of preamplifiers that provide a natural match for the MCH-K38.

The new HPA-9 is a natural choice – it might be quite simple and small, but I’ve had one at home for months now and just love it. The HPA-9 is far more transparent than a product at this price level has any right to be. While there are only 3 inputs (2 line and one phono) it does have two sets of outputs which makes it perfect for bi-amping the K38. In addition its one of the few preamplifiers that will not just match the MCH-K38s extraordinary bandwidth – with a frequency response of 0 Hz to 200KHz (-3dB) – it goes even further which is all the more remarkable for the cost. Team it up with the matching DAC-9 and you’ve got a wicked combination that will do justice to all formats.

The DAC-10H combines all of the features of the two 9 series source components and takes them further again.

Of course there is nothing stopping you using other components with the MCH-K38. It is a power amp after all and it could well be a significant replacement for and upgrade over almost any other power amplifier.

The Conclusion.

The MCH-K38 presently stands as NuPrime’s best sounding single box power amplifier. It is also by far the most powerful with 8 x 210 watt channels or by simply flicking the back panel switches, 4 x 400 watts.

By NuPrime’s own standards it is both their best value and performance for high performance stereo systems where bi-amping is an option. It delivers massive headroom with total of 800 watts per speaker in this context.

It is the finest multichannel power amplifier for surround sound systems with explosive power delivery and a level of fidelity we have not heard matched in any setting.

NuPrime MCH-K38 8 channel power amplifier NZ$4500 including GST.