*DEMO* NuPrime AMG STA

Demo example of 1 NuPrime AMG STA unit in excellent condition!
Sold with a 1-year warranty.

The AMG STA is a substantially upgraded STA-9. It operates in the performance class of the 10 series, but takes a slightly different approach to reproduction and offers more options, since the amplifier can be used in both stereo and mono.

The AMG STA is based on several modern innovations in power amplifier design. Among its key features are a 1 MOhm input impedance, high instantaneous current for power delivery, a 700 kHz switching frequency, and a Single-Ended Non-Negative Class A module working together with a Double Feedback Class D module to deliver 300 W of mono power.

The AMG series' front panel reflects its spirit. It is milled from 15 mm hard aircraft-grade aluminum on a four-axis CNC machine using diamond cutters through a 48-step process. Design details such as the 3D-floating logo, the curved surface around the front-panel power switch, and the diamond-cut edges bring ultra-high-end quality to the AMG series' more accessible price point.

The AMG STA's circuit board integrates shielding for the ground lines to keep out external interference. The JFET, with its 300 MHz bandwidth, provides very high input impedance and fast response across a wide frequency range. The dynamic design and single-ended Class A circuit enrich the natural second harmonic.

The design also allows even the most subtle details in the music signal to pass through the entire chain. The transparency of the reproduction is remarkable in this class, with a confident ability to build a highly detailed soundstage.

The AMG-STA uses the "Single-Ended, Non-Negative Feedback" Class A module together with a new "Double Feedback" Class D circuit. The Class D amplifier's oscillating frequency has been raised to 700 kHz, which is 1.4 times that of the STA-9.

The power supply uses a specially wound 380 W transformer that provides 30 percent higher peak power than a transformer of equivalent volume.

A heavy-duty welded conductor runs from the input connector to the transformer for maximum power transfer.

So how does the AMG STA sound better in mono mode, beyond its higher power compared with stereo mode? The established method of bridging a stereo amplifier to mono uses a series of operational amplifiers (OPA) to invert the input signal to one of the stereo channels, thereby creating an out-of-phase signal that can then be combined for higher power. Instead, the AMG STA uses an innovative bridge circuit that we call Single-Ended Direct-Inject Bridge Technology, whereby mono mode not only delivers more than twice the power but also sounds livelier and more dynamic.

Listening impressions

With improvements in every area, the bar has been raised for what can be achieved in a compact format.

The AMG STA has a character all its own and is therefore difficult to compare with the Evolution One, which partly shares its design, or with the similarly priced ST-10. The AMG STA sounds smooth and relaxed. Detail, resolution, dynamics, and speed are at ST-10 level, but the tonal character is noticeably different.

Compared with the Evolution One, it shares the ability to reproduce the details of a recording effortlessly. But the AMG STA does so in its own way. Where the Evolution One has an inviting warmth, the AMG STA wants to draw the listener toward it. Instead of a sparkling sound that quickly pulls you into the performance, the AMG STA has a temperament that slowly draws you into the music.

Tonally, the AMG STA leans toward the full and rich, giving instruments and voices extra body, weight, and harmonic richness. It may not be the most precise reproduction, but it makes jazz and vocals almost addictive. At the same time, it can remove some of the rawness from rock and electronic music, making it somewhat less exciting for some listeners.

The soundstage has an appealing quality. A linear presentation is like floodlights shining on all the musicians so that everyone is seen equally clearly. The AMG STA instead has more of a spotlight effect, with individual musicians brought into focus to capture your attention.

It is difficult to describe the AMG STA's sound in measurable terms, because its presentation differs so clearly from the other series. You need to listen for yourself to hear it.

Christiaan Punter, HFA (hifi-advice.com)
AMG-PRA + AMG-STA form a beautiful combination, not only visually but also in terms of tonal synergy, with the preamplifier's robust and full sound perfectly complementing the power amplifier's somewhat leaner balance. The overall result is a musical, consistently engaging sound that is stable and full, smooth and refined yet highly detailed and transparent, with perfect timing and great dynamics. Honestly, I have not heard a better amplifier for 3200 euros, whether integrated or separate.

As good as the combination is, the AMG-STA power amplifier is truly the star of the evening. On its own, it achieves a level far beyond what one could expect from an amplifier in this price class. More precisely: if the preamplifier already performs far above its price, the power amplifier steals the show because it plays at the same level as amplifiers that normally cost several times its modest price of 1595 euros. I am not joking!

Combine the AMG-STA with a good volume-controlled DAC and you have an almost unbeatable system. Between one or two amplifiers, if there has ever been an obvious choice, this is it. The pair simply raises performance in every audiophile parameter without harming emotional involvement.

As should be clear by now, I am definitely impressed by NuPrime's power amplifiers. First, the ST-10 proved to be a keeper, then the ST-10 Monos showed that the concept could be taken further, then the AMG-STA showed that Class D can be just as "analog" and refined as the finest linear power amplifiers, and now the AMG-STA pair has raised the bar even further. Although the ST-10 and ST-10 Monos still have their unique character, the AMG-STA pair is currently my personal reference among affordable power amplifiers with genuine high-end ambitions.

Whether used as a stereo amplifier or as a dual-mono pair, the AMG-STA is an absolute HFA favorite.

Specifications:

• Stereo Power: 2 X 130W @ 8 Ohm & 2 X 200W @ 4 Ohm
• Mono Power: 300W @ 8 Ohm & 320W @ 4 Ohm
• Rated / Peak Current: 10A / 15A
• Gain : 26 (stereo) & 52 (mono)
• Signal to Noise Ratio : 100 dB @ 10W
• THD+N : 0.006
• Frequency Response : 10Hz~50K Hz +-0.2dB @ 8 Ohm. 58K Hz @ -3dB
• Input Impedance: 1M Ohm
• Sensitivity: 1.2 Vrms @ Stereo; 0.95 Vrms @ Mono