– Mikkel Gige, HiFi4All
Does hifi need to take up a lot of space to be good? At least that doesn’t seem to be the case with the new amplifiers from Nuprime’s AMG series. But then there is also plenty of space inside the slim and attractive cabinets. And as something rather special, Nuprime has chosen to give them an input impedance of 1,000,000 (one million!) ohms. It was said to make it easier for either signal source or preamp without adding unnecessary noise. But one thing is theory, and something else is practice… and it is my experience that impedance matching of devices is not without importance, and it also turned out to be true with the AMG amplifiers.
The AMG series contains the preamplifier PRA and the power stage STA, and they share the same cabinet, so they can be easily stacked, or just look good placed together… The cabinets are made of strong bent steel plate for the chassis and top shroud, and the latter is extended beyond the rear edge, so plug to hide the cables. Due to the low height of the cabinet, these would otherwise be completely visible. The front is made of aluminum and milled in a nice 3D finish, where the logo almost floats in front of the front.
PRA has 4 inputs – of which 1 balanced, and 2 outputs – again 1 balanced. The PRA is a balanced construction, and has double circuits throughout. The circuitry for the signal is based on J-FET’s running in pure at. A, and the volume control is digital in a kind of step-ladder principle. The power supply is well-dimensioned with a C-core transformer and a small stock of chargers. There are several options for settings with PRA, both on gain, phase and a variable loudness function, which only amplifies the bass, in small easy steps, without the sound being negatively affected. It can be advantageously used together with smaller speakers.
The STA power stage is a hybrid of A and D, and again J-FETs are used in the input, in a balanced construction. There is a good amount of space inside the small cabinet, which is mainly due to the classic linear power supply, which takes up almost half of the space, and consists of a 350VA toroidal transformer and a storage of 8800µF charging capacitors. And that’s how it is when you use at. D, where the output circuits do not take up much space, despite a high efficiency. In fact, both the input and the power filter individually take up the same space as the output!
The STA is also versatile, offering both balanced and unbalanced input. And then it can be bridged if you need extra watts for inefficient speakers. And thumbs up for Nuprime sticking to their principle with linear power supplies for Kl. D exit stage! Too many manufacturers choose the easy solution with switchmode supply.
And also thumbs up for making small, stylish amplifiers that prove that good hi-fi doesn’t need to take up a lot of space…
The PRA preamplifier was first connected in front of the Norma power stage, and the immediate impression is that in terms of sound there is not much difference to the Vincent preamplifier. AMG PRA is very musical with that romantic little twist of warmth that I appreciate so much. And it is clear what the intention has been on Nuprime’s part in their use of J-FET’s.
And then it sets a dynamic from the day, which almost gives Vincent red cheeks. There is a pressure from the drums, so that you just lift up a little in the seat, and in general a “crispness” of the details, which usually cost more. But it can also sound a bit like too big a turbo has been put on the engine. Because even though the bass is deep with plenty of weight, I miss some nuance, and it can become too “boomy” if too many things mix together in the deep frequencies.
At the other end of the scale, there is not quite the amount of air I am used to, and there is a slight tendency towards “tst” sounds, depending on the source material. But the soundstage is large and reaches almost as far out, up, and in the back as I know it. And one thing that particularly shines with PRA is the Q-sound on Amused to Death. It is actually just a notch clearer than the Vincent, who is otherwise the ranking champion in this discipline!
The midrange is right by the book, with a naturalness and straightforwardness, and a presence and realism that one can almost only dream of. AMG PRA is not alone in this, and it seems that more manufacturers are starting to realize the importance of getting this area to sound right… because often the other thing goes without saying! And if possible, the realism is almost a notch too much with PRA… anyway, I just had to turn it down a bit for Roger Waters at intervals, but it’s also an unusual recording in this discipline. But it underlines PRA’s dynamism and willingness to be impulsive!
A few nice details about the PRA are the versatility of both inputs and adaptations it exhibits. For example, there is no difference in the sound from the balanced and unbalanced inputs and outputs. And the possibility to adapt the sound, I tried with input from the record player, which sounded a bit dull and woolly with normal gain. But when it got an extra shot of gain, the sound lived up to what was described above. PRA also has a loudness-like function, which amplifies the bass in very small steps, in a very nice way without affecting the sound negatively. With large speakers it is by no means necessary, but with smaller speakers it is a nice option!
The effect stage STA is very similar to the playing style of the PRA, but despite the same versatility, the STA is somewhat more demanding. Since the Vincent preamp is unbalanced by nature, I started out with this… but the soundstage wouldn’t really fall into place. The sound didn’t quite reach the speakers, and the soundstage was flat without depth. And the bass sounded like what was known in the “old days” as typically “at D-bass”: Lots of level and weight, but no details and nuances!
It was switched back and forth several times, both as stereo and mono, but it wasn’t until I switched to the balanced inputs (with adapters) that things started to click. But more was needed… and because the STA has a very high input impedance, you shouldn’t expect that you can plug in any preamplifier. The matching PRA has an output impedance of only 100 ohms, which is quite low, and clearly made to match the STA’s 1-million(!) ohm input. But luckily the Vincent has two outputs of 600 and 50 ohms respectively, and with the latter it hit 100% with the STA.
But then the sound also immediately became much more forgiving, and the sound image grew clearly in all three dimensions. Likewise, the bass became more nuanced and detailed, while the heaviness was still present. And that meant I could now start listening for other things in music. At the same time, it was a great musical pleasure to listen to STA. And it was here that it was clear that the sound is very similar to PRA. However, STA does not have quite the same punch and dynamics as PRA, but it is also quite unique in that area.
It also meant that I actually stopped thinking more about the sound and instead just enjoyed the music. As if by magic, presence came into the music, and both voices and instruments took on a naturalness a la what I know. And the sound just stretched further up towards the high frequencies without artifacts or anything else that could disturb the experience.
As said, STA is also versatile and can be bridged to monotrain. But it wasn’t necessary at all with the large efficient Audiovectors, and one STA pulled them off with flying colors without breaking a sweat! In fact, the only thing I experienced with two STA monostages was that the gain increased very clearly. There was no difference to track otherwise, which is actually quite an achievement in itself. It’s usually not my experience that bridging does anything good to the sound. But here STA just shows that it is the exception that proves the rule!
There is no doubt that Nuprime has made a couple of really nice, small amplifiers with the AMG models PRA and STA. It’s also an exceptionally versatile pair of amps that can adapt to most anything. But due to the high input impedance of 1 million ohms, you have to pay a little more attention to which devices you connect them with, and here you should ideally go down to 100 ohms output impedance (or lower)!
Fortunately, the reference setup in the listening room is precisely geared for this, so I could get the maximum out of the PRA and STA. And they provide a fantastic musical experience, with that little twist of warmth that I just like. Technically, they also do well, but for natural reasons do not quite reach the level of the amplifier set in the listening room. But… PRA actually has a few tricks up its sleeve that make the Vincent a bit red-cheeked.
And that means that without blinking an eye, I give the Nuprime AMG PRA the distinction of “Best Buy” along the way!
Link to the review --> https://hifi4all.dk/content/templates/anmeldelser.asp?articleid=3443&zoneid=3