NuPrime AGM STA stereo power amplifier
Review samples provided by Dimex
Retail Price: 1.595 euro
Regular readers will know that I have very good experience with NuPrime amplifiers. After years of use with all sorts of speakers and countless comparisons with other amplifiers, I still feel that the ST-10 stereo amp with its proprietary Class-D technique offers a unique proposition and amazing value for money. It’s not without reason that I still use it even in the context of equipment costing tenfold.
Of course, at 1.595 euros, it is not going to outperform state-of-the-art, high-end products, but in certain important aspects it equals some of them and in other aspects, it comes far closer than it should when considering its modest cost. At the exact double rate of 3.190 euros, the ST-10M mono versions retain all of what makes the stereo model such a great amp while addressing the main areas in which the stereo model falls short in my opinion: treble refinement and overall resolution.
Up for review here is another NuPrime amplifier but, this time, one with an enhanced working principle: the AMG STA that offers a different sonic perspective and costs exactly the same as the ST-10.
AMG STA Technical
The ST-10 and ST-10M amplifiers are pure Class-D designs albeit using a proprietary circuit. The AMG STA amplifier uses a similar circuit but with the switching frequency raised to 700kHz and fitted with an analog input with a 1M Ohm input impedance. Another important difference is that the ST-10 uses a high-end opamp for the input stage whereas the AMG STA uses discrete Class-A transistors.
I asked the manufacturer for more information. Jason Lim replied:
“Our design is different from other Class A + D designs, because we designed the Class-D amp ourselves, which enables us to combine the Class-A preamp stage in series with the Class-D power stage. For other manufacturers who have to purchase an OEM Class-D module, the principle of current dumping is to take a Class-A in parallel (bridge balanced) to supplement the sound quality of Class-D. This method addresses the harmonics/warmth issue of Class-D so that it can sound richer, but it still doesn’t fix the sampling rate problem of Class-D. Over the past 15 years, the switching frequency/sampling rate of Class-D amps has steadily increased, but for off-the-shelf amp modules (ICEpower, Hypex, and other lower quality class-D amps using reference designs from MOSFET suppliers), they have cost consideration and other priorities. Nuprime continues to push the envelope of Class-D design, such as using Class-A transistors and also raising the switching frequency to 700KHz (far above other off-the-shelf Class D modules). Therefore, the approach taken by Nuprime Class A+D design is not only to provide “richness”, but also improve the resolution.”
There is more to read more about this, as well as other techniques, on the Amp Design page of the NuPrime website.
Powered by a large toroidal transformer and with 2 x 130 Watts into 8 Ohms and 2 x 200 Watts into 4 Ohms, the AMG STA will be powerful enough to drive any loudspeaker, including Apogees, Logans, Magnepans and Magicos. And yes, that includes the rather difficult Q5’s, as I will report on further down. Naturally, if you push it far enough I imagine that there will ultimately be a limit to the available current. But for the playback levels that I can tolerate and with any of the speakers that I tried it with, it is more than sufficient.
With a smart front panel but an otherwise simpler enclosure, NuPrime managed to keep the price of the AMG STA the same as for the ST-10, in spite of more complex electronics. The front panel is machined from a solid piece of aluminum with a protruding NuPrime Brand name. Unusually, the power LED is mounted underneath and behind the power switch, lighting it in a nice and understated fashion when viewed from the listening position.
When standing up and looking at it from an angle, however, it is super-bright. Between this solution and the highly dimmed deep blue LED in the ST-10, I prefer the latter.
Jason Lim responds: “Thanks for your feedback. We will make an adjustment by adding a filter to the LED”.
The speaker connectors are very tightly-spaced on the ST-10, and the same is the case on the AMG STA. There simply isn’t much real estate to begin with. But due to the louver-like extension on the rear, spades can only be inserted from below, meaning that the AMG STA needs to be positioned at the edge of the shelf or component underneath it. Thankfully, NuPrime did clear enough space to allow the use of beefy high-grade IEC power connectors.
Bananas work just perfectly… but when using Spades, especially those with long metal parts such as with the Jorma cable, one has to be very careful not to make a short
Connectivity matters and working principles aside, from the moment that I switched it on, I heard that the AMG STA is something special.
System Context
I will listen to the AMG STA, first using different setups in the same room, consisting of either the Aqua Formula xHD DAC with V2 output board and Audio GD Master 1 combo, or the CH Precision C1 DAC. The source in both cases is the Antipodes CX running Roon via HQPlayer to the Aqua LinQ, connected via AQLink I2S cable to the Formula xHD and via a Jorma AES/EBU cable to the C1 DAC. The loudspeakers are the Magico S1 MkII’s and, in a later stage, the WvL SONs. I will also briefly involve the AMG HPA, an analog preamplifier and headphone amplifier.
Lastly, I will also listen to the AMG STA power amp in audio buddy Niels’ setup, which in its core is formed by the Aurender S10 music server, Mola Mola Tambaqui DAC and Spectral DMC-30SV preamp. Here, it will drive the Magico Q5 loudspeakers.
Thanks for the informative review of the Nuprime AMG STA and all your other reviews for that matter. I always greatly enjoy your reviews. It’s also a wise decision to test equipment in someone elses system in order to get a broader grip on how the equipment under review behaves with other components. Keep up the good work.
If you look at the specs for NuPrime’s amps, their SBR specs are not very good. Don’t know about you, but I’m not a big fan of amp noise.
I’m not sure what you are referring to but I judge audio equipment by ear, not by spec.
The SNR is not a good measure of a state of the art amp’s performance, because AMG STA has PURPOSELY added GOOD 2nd-order harmonics. Those are the characteristics that makes the amp sounded “real”, where an old violin sounded like one, etc. SNR measurement won’t be able to differentiate good “noise” versus bad noise. I bet you have not listened to NuPrime amps before, otherwise you won’t be making this statement. Give it a try.
Ah, SNR! You wrote SBR…
You are correct in that they have carefully added 2nd order harmonics, just like it would happen with tube amplifiers. I’m not saying that more distortion is better (in principle it is not). But in important aspects, this can actually help create the illusion of reality. On the other hand, it takes away some precision and transparency. Still, it’s always about weighing various aspects against one another and it is the end result of all combined measures and techniques that counts. That, and the end user’s set of preferences and of course the system synergy. But rather than discuss the good or bad of this in theory, I prefer to just listen to the products that I review.
Hello
It is always excellent to read your reviews !!! I find that your reviews are well done with comparisons with other products and sound specifications which are well rendered. your report is rich in lessons. thanks again.
I want to clarify about the “adding” of 2nd order harmonics. We are not dealing with digital design here. So there is no such thing as simply “adding” for the sake of having some sound characteristic. It doesn’t work like this in the actual design. What we did was to use the Class A transistors circuit to shape the sound, just like what linear amps would do. So if you want a warmer linear amp, you would pick the tube or transistor with the sound characteristic. Likewise, the transistors circuit that we created, would have higher order of even harmonics, which existing in linear amps as well.
First of all a big thank you for your site which is worth gold to me.
Concerning the AMG STA in stereo presented here, in view of the increase in quality of the ST10 in mono (resolution-refinement), and idem for the STA9 that I had in stereo then 2X monos with a nice improvement in dynamics, aperture and depth as well as in bass resolution in particular, I can not help wondering about the contribution of 2 AMG STA in mono … This to improve, perhaps, the dynamics which seems to you to be a little lacking and in particular for the strength of the low frequencies, which are also important to me.
This is for my Harbeth M40.2 for which I was thinking of changing the current Modwright KWA150SE amp for a Bryston B4 cubed. Its price is more than twice as much as 2 AMG STA for a final rendering that would then seem quite close?
Finally, which power cables would you recommend for the AMG?
Thank you in advance for your opinion
A pair of AMG STA’s is certainly worth investigating and is on the list of things to do. But I can’t guarantee that it will materialize.
Hi
Reading your review of the NuPrime Evolution Ones it sound a lot like the AMG STA. Can you comment on the difference, even though you didn’t have them side by side? Could you please also write a sentence or two about the sonic difference between NuPrime and the Audio GD mono blocks?
Thanks for great reviews. Can’t wait to read about Vinnie Rossi and Classé.
Stay safe,
Per
If my two reviews read similarly then I’ve not done a good enough job to differentiate. With my current knowledge, I feel that the AMG STA is even more refined and fluid than the Evo Ones. Also, I feel that the little stereo amp is more fun to listen to than the more business-like Evo Ones. The Audio-GD’s are the best amps I’ve heard bar the CH A1.5. That’s only fair given the difference in size, weight and cost. The Classe is only reviewed for Dutch printed magazine HVT. I don’t think I’ll write an English review for HFA but you never know.
Christiian,
I did have a chance to test the Classé Delta Pre + Classé Delta Stereo Power Amp at home for a week, so I was extra curious to find out if we had similar findings. The fan noise was too loud for me. No need to look for dark background in other components if you have a fan noise killing all of it. I found it to be rather even in the frequency delivery but I lacked some speed in the transients. High quality design and material but I think the price was too high compared to the performance. Bass delivery wasn’t to my liking at lower volume levels. Also very narrow angle of response for the remote. For this amount of money there are other more tempting options, in my book.
My apologies for misspelling your name Christiaan, sorry about that.
No probs, of course:-)
Hi Per, I agree on several points, especially the fan noise. Way too audible indeed. I’ve fed that back to the manufacturer, hopefully, they can do something about that. Without going into detail, in general, I think more highly of the amp than the preamp.
Hi ..all you need is the Nuprime Dac évolution review 🤪🤪
Happy year 👍👍
Christiaan another fantastically thorough well written review thank you. I have zero interest in Class D or SS at all for that matter and yet I was thoroughly entertained. Happy New Year!
Cheers,
Jon