Review samples provided by Dimex
Retail Price AMG STA-SE: 2.595 euro
Upgrade from AMG STA to AMG STA-SE: 699,- ex labor
When I first heard the AMG STA in 2020, I was amazed at the sound quality it delivers at its price level. As I observed in the review, “Changing from the NuPrime ST-10 to the NuPrime AMG STA was like changing to a completely different amplifier brand. While it does not have the ST-10’s sonorous ballsiness nor entirely all of its dynamic impact, otherwise, it seriously ups the game… the AMG STA raises the quality in some areas into high-end territory.”
I continued observing that some of the AMG STA’s aspects, such as its fluidity, delicacy, and refinement, reminded me of classic Jeff Rowland amplifiers, class A/B ones, such as the Model 6 monos and Model 10 stereo, mind you, not their later class D designs. To add some perspective, the cost of these classic amplifiers was quite serious at around 15K and 11K, respectively, back at the turn of the century, indicating just how class-defying the AMG STA’s performance is.
With the AMG STA-SE, the company has issued a successor. With this new Special Edition model, the company aims to narrow the gap between the different sound characteristics of models such as the ST-10 and Evolution STA on the one hand and the AMG STA on the other while addressing some of the weaknesses compared to the ST-10 as mentioned in my review, such as reduced robustness, tonal saturation, and body. How an engineer can correlate listening impressions with the amplifier’s design remains a mystery, but the proof should be in the pudding!
A closer Look
Ideally, I’d have the original AMG STA on hand for a side-by-side comparison, but alas, the model was out of stock, and I no longer had mine. However, I do still have vivid memories of it, as well as inside pictures. Curious, I opened the new model to have a peek inside. On the surface of it, the two amplifiers look very similar.
Above: original AMG STA; Below: new AMG STA-SE
In comparing the original model to the Special Edition version, there are only a couple of differences I can discern:
- Thicker wires connecting the fuse to the PCB
- A different (regulator?) IC in the input section
- A new NuPrime-branded power module
The “Power Engine” is a low-power switching power supply (SMPS) for low voltages on the amp board. The large linear power supply provides high voltages for the Class-D power stage. According to the manufacturer, they have made a breakthrough in SMPS design that can rival linear power supplies. This “Power Engine” is the first use of such a design for AMG STA-SE.
Above: a closeup of updated Power Engine in the new AMG STA-SE
But there is more to it than meets the eye. The manufacturer confirmed that although the architecture remains the same and the boards look much alike to the naked eye, numerous modifications have been implemented, leading to significant improvements.
Special Edition Enhancements (AMG STA-SE vs AMG STA)
- The enhanced Class-D circuit boasts a 30% reduction in MOSFET temperature during high-speed operation exceeding 750kHz, enhancing energy efficiency and ensuring sound stability.
- The PWM waveform has less ripple, resulting in lower noise and higher efficiency.
- Employing aerospace-grade ultra-high-precision resistors with a minimal error margin of 1/1000, the system exhibits ultra-low drift, with a temperature drift coefficient of only 15 parts per million. This ensures that negative feedback sampling remains unaffected by external temperature variations and environmental factors, enhancing accuracy and detail in music reproduction.
- A newly devised and fine-tuned secondary negative feedback circuit.
- A large-capacity current power supply capacitor design with low-impedance routing for the primary current path, boosting instantaneous supply current to 1.5 times that of the original AMG STA design.
- A newly developed AC power supply minimizes external radiation noise interference, while a redesigned SMPS power module ensures an ultra-low-noise system power supply for circuits that require low voltages.
Why Resistors have such a significant impact in Switched Amplifiers
Amplifiers, preamps, and power amplifiers with negative feedback amplification circuits require resistors with precise temperature coefficients and accuracy. These resistors significantly impact sound resolution and detail. Changing other positions has proven ineffective or even detrimental.
NuPrime’s analysis revealed that the amplifier’s amplification factor at open-loop gain is in the tens of thousands. Negative feedback reduces this to around ten times, relying heavily on feedback resistors. NuPrime extensively researched various types, brands, and shapes of resistors, meticulously measuring their accuracy and fine-tuning their positions. This process required substantial effort and a significant amount of experimental data. Even the slightest variation can impact the outcome.
The result is that negative feedback sampling remains unaffected by external temperature variations and environmental factors, enhancing accuracy and detail in music reproduction.
Connections
The interlinks I used are Driade Flow Link Reference 808, which I have in XLR and RCA versions. These two cables sound almost identical, and so do the amplifier’s XLR and RCA inputs. I currently prefer to use XLR because that works best with the CH equipment, and a given other situation may dictate other decisions, but the NuPrime amp has no preference.
With such a small form factor, there’s no abundance of space for connectors. Still, the AMG STA-SE offers everything you need: a switched IEC inlet, fuse, speaker connectors that accept bananas or spades, a mono switch, and both balanced (XLR) and single-ended (RCA) inputs.
Out of fear for a short, I used adapters to connect the Jorma Unity speaker cable’s spades. However, the Driade Flow Reference 808‘s banana connectors fit directly and very comfortably.
The power cable was the exact same as used for the CH amp: a Belden 19364 (latest 2.08mm version) with Bals Schuko and Oyaide C-004 IEC. The only difference is in the IEC end. The CH amp takes a 20A connector but Oyaide does not provide the C-004 in this version. Instead, I use a simple Schurter with a very tight grip that to these ears sounded better than Oyaide’s gold-plated C-279 20A variant that I tried. The latter sounds very similar to the C-079: very smooth and mellow.
Price
At the time of review in 2020, the AMG STA was priced at a mere 1.595 euros. Over the last few years, due to rising energy prices and crazy price hikes on bare aluminum and other metals, everything has become more expensive. As a result, the AMG STA was 1.850 in 2023 euros. The AMG STA-SE is priced at 2.595 euro. Granted, that no longer sounds like the ultra-bargain it was before, but considering that all audio equipment prices have increased significantly, I would say it is still very reasonable. That is, of course, if it delivers on its promise!
Review Context
The AMG STA-SE will be listened to in the main system using the Precision C1.2 and Aqua LinQ streaming endpoints with the Antipodes Oladra running MinimServer. The rest of the system comprises the CH Precision L1 preamplifier, CH Precision A1.5 power amp, and Magico S1 MkII speakers. Besides Driade Flow Link Reference 808 and Flow Reference 808 speaker cables, I also used Jorma Unity speaker cables.
Next: Listening
And, of course the question: did you try two SEs in mono block config? How did that go?
I was supplied with only one SE so I did not do that test at this time. However, I have reviewed the ST-10M monos as well as the AMG STA in mono mode. From these reviews, I know that doubling up a NuPrime amp is very beneficial.
Nice in depth review again sir Punter! Thanks!
The Jeff Rowland models you mention at the beginning of your review were cheaply made amps which used poor connections inside and poor switching power supplies. The only thing about them that smelled of high end was their chassis and brand name. This review just knocked your credibility down about ten rungs on the ladder for me.
I have owned and reviewed several Jeff Rowland preamplifiers and power amplifiers, both their linear and switched ICE and Pascal designs, as well as their DAC, and many of the products are reviewed on this site. There’s also a JRDG company special with all ins and outs of all their products which is worth looking up if you’re interested in the brand.
Pertaining to this NuPrime review, when I recall the original AMG STA, I was not referring to the Class-D Rowlands (which I also do not rate very highly) but specifically to certain classic Class-A/B models such as the model 6 and model 10. Both are linear designs, even if the model 10 had a switching power supply.
Hi Christiaan, Thanks for the answer the other day on Vineshine. Question. As you know I ended up getting a pair of these way back running them mono thanks to your initial AMG STA review. What do you think they would sound like with the SE upgrade?
I’ve not tried the SE in mono but I would assume it behaves the same way as the AMG STA. The SE upgrade improves the tonality and elevates the realism, and for that, it is highly recommended. But to some extent, it also depends on whether or not you want a fuller, slightly darker, and more saturated sound as opposed to the leaner and airier sound of the original. That’s a personal matter. If you feel your balance with the original is ideal right now, I would suggest simply getting a demo first.
Not sure if you recall I have the ML 15As connected to a Bryston 4b3. I had done an A/B test with my new at the time AMG STA. I ended up leaving the Bryston with the MLs because of the warmer presentation. The Mono AMGs (purchased another one) went to my Tektons in another location. Except the Tektons are no more. I didn’t like the sound stage and they were “too large” said…this crazy woman that lives with me. I now have Magnepan LRS+ with the AMGs. So yes the definitively need to be “warmed up”, not warmed up like break in, warmed up like right now jazz sounds flat. Based on what your saying, I don’t need the demo, I should just get the upgrade.
Hi Marc, reading your summary, I would say the SE upgrade would indeed be a good step in the direction you desire. That said, you may still want a warmer or harmonically richer sound with the Maggies. The AMG-STA SE is definitely fuller and richer in harmonics than the origial but it remains essentially quite neutral, which I think is a good thing. But it does not emulate a tube sound, so to say. If that is what you need or want, then the new NuPrime may still not provide what you are after. Ultimately, there’s only one way to find out… I’d be very interested to hear your feedback if and when you have taken the plunge.
HI Christian, in the past you have made comparisons between the various Nuprime power amps with close attention to the Evolution STA as the gold standard. I don’t see the Evolution being mentioned in this review at all for comparison, why is that??
Hi Luke, well, the AMG STA SE is the successor of the AMG STA, so it makes sense to compare the two. The Evolution STA sits in a different price range. But it also sounds quite different, making it hard for me to provide any meaningful comparisons to the AMG STA variants based only on memories.
OK thanks I am evaluating the amg sta se now and after nearly 400 hours of burn in it is now beginning to show itself to me as a much more accurate and somewhat different sounding (in a good way) unit compared to the standard version.
Hello,
How does it compare with NAD M23 ?
Thank you
I have not heard the M23.
Hi Christian,
I just received the upgraded SE version of my 2 amps in mono setting and I have to say, this is a nice jump to higher quality. To make it short it sounds more real, more transparent with more additional details, more dynamics, deeper stereo imaging, tighter bass. Everything is more precise. Easy to have goosebumps listening a voice here or stamp your foot listening a band.
It’s a no brainer upgrade for everyone looking the cost vs the benefit and we can congratulate Nuprime to propose this option. The French distributor never answered to my calls nor my emails, and I contacted Nuprime in Taiwan to do so. I received all instructions to proceed through their tech support in Hungary (Krisztian thanks!).
You said it sounds like Pass Lab amp, I had one integrated in the past, I much prefer this Nuprime combo by far.
Thanks for the very nice feeback, Phil!
Does Phil have any disclaimers he’d like to add, any association to NuPrime perhaps, cause Phil’s review sounds an awful lot like a marketing piece.
I do not have any link with the hi-fi world, I’m just an happy customer after 40 years of up and down with products and sometimes expensive products. It’s not so often a manufacturer proposes an upgrade which is accessible. And not often a brand cares about the request of a customer and delivers.
Martin Logan is also one of them from my personal experience as well.
Well then, heck of a review of their upgrade. Sounds like a no-brainer upgrade. One thing I did already agree with, it was nice they offered the upgrade to existing customers at the fair price they did. The AMG amps weren’t that old, simply replacing them with a newer model that fast would have been frustrating.
I also purchased these with new boards and can say it was certainly a step up from the original version and although I had the original boards I had no intention of reversing them. However, I have found the Audio GD master 2H monoblocs drive my system much better.
More than a month after the SE upgrade, Î’m impressed by the music delivered here,
Just so realistic, so fun ! confirming my initial post.
Thèse little amps are a true value I will keep Théo for a long time. Amazing.