NuPrime AMG STA

The AMG series front panel embodies its spirit. It is milled from a 15mm hardened aerospace aluminum alloy using a four-axis CNC machine with a diamond cutter through a 48 steps process. Design elements such as the 3D “floating” logo, the curved surface around the front panel switch, and diamond-cut edge bring the quality of ultra-high-end audio products to the affordable range of the AMG series.

Technology

AMG STA PCB integrates ground wire shielding to isolate external interference. The 300 Mhz bandwidth JFET provides ultra-high input impedance and wide-band fast response. The dynamics of the design and the single-ended Class A circuit enrich the natural second harmonic.

This design allows the most delicate details in the audio signal to carry through the chain. The level of transparency in sound reproduction is genuinely astonishing in this class of equipment, with a deft in creating a highly detailed sonic imagery.

The AMG-STA uses the “Single-Ended, Non-Negative Feedback” Class-A module partners with a new “Double feedback” Class D circuitry. The Class D oscillating frequency has increased to 700kHz, which is 1.4 times that of the STA-9.

Power Circuit

The power supply uses a 380W special winding power transformer, which has 30% more peak power output than a similar volume transformer.

The AC power input from the Inlet Connector to the power transformer utilizes a high current welding line to provide maximum power transmission.

The standard method for bridging a stereo amp into mono employs a series of op amps (OPA) in order to invert the input signals to one of the stereo amp, thereby creating an opposite phase, which can then be combined to increase power. Conversely, the AMG STA's innovative bridging circuit utilizes a design we call Single-Ended Direct-Inject Bridge Technology, in which the mono mode, in addition to acquiring more than double the power, sounds livelier and more dynamic.

Listening Impression

With improvements to every area, the bar has been raised for what is achievable with audio performance in a small form factor.

The AMG STA has a flavor of its own, so it is hard to compare it with the Evolution One, which derives some of its design from or the similarly priced ST-10. AMG STA sounded smooth and relaxing. Detail, resolution, dynamics, and speed are in the ST-10 ballpark, yet the sound is quite different.

Drawing comparison with the Evolution One, they shared a trait of ease in reproducing the details of the recording that comes before. However, AMG STA does things differently. While the Evolution One has that inviting warmth, the AMG STA wants to allure the listener. Hence, instead of glitz and glamour, which pulls you in quickly into the performance, the AMG STA has a demeanor that slowly brings you into the music.

Tonal qualities of the AMG STA lean towards being full and rich, so instruments and vocals seem to gain extra body, weight, and harmonic richness. It may not be the most accurate reproduction but does make Jazz and Vocal pieces highly addictive. It may take away the raw edge of Rock and Electronic music and sounds less exciting for some.

The sound stage has an attractive characteristic. A linear presentation is like having floodlights shining on all the performers such that everyone can be seen equally well. The AMG STA, however, has more of a spotlighting effect, where performers are focused on getting your attention.

It is tough to put the sound of the AMG STA into measurable attributes as the presentation is quite different from the other series. You'll need to try it and hear for yourself.

Christiaan Punter, HFA (hifi-advice.com)
The AMG-PRA + AMG-STA form a beautiful combo, not only visually, but also in terms of sonic synergy, the preamp's robust and full sound perfectly complimenting the power amp's slightly leaner balance. The combined result is a musically always engaging sound that is solid and full-bodied, smooth and refined yet highly detailed and transparent, with perfect pacing, and great dynamics. Honestly, at 3200 euros, I haven't heard a better amplifier, either integrated or separates. As great as the combo is, the AMG-STA power amplifier really is the star of the show. On its own, it is capable of performing on a level that is well and truly beyond what might be expected from an amplifier at its price point. To be more precise: if the preamp already performs at a level that belies its price sticker, the power amp steals the show as it has the ability to perform on the level of amplifiers that typically cost multiples of its modest 1,595-Euro price. I am not kidding!
Combine the AMG-STA with a great volume-controlled DAC and you'll have an almost unbeatable system. Between single and dual amps, if ever there was a no-brainer decision, this is it. The pair simply raises the performance in each and every audiophile parameter, without harming the emotional involvement.
As should be clear by now, I am definitely impressed by NuPrime power amplifiers. First, the ST-10 proved to be a keeper, then the ST-10 Monos proved that the concept could be taken further, then the AMG-STA proved that Class-D can be as “analog” and as refined as the best linear power amplifiers, and now, the pair of AMG-STA's have further raised the bar. Although the ST10 and ST10 Monos still have their unique flair, as of now, the pair of AMG-STA's are my personal reference in the field of affordable power amplifiers with true high-end aspirations.
Whether used as a single stereo model or as a double-mono pair, the AMG-HPA is an absolute HFA Favorite.