Power amplifiers stereo — Nuprime Audio AMG STA-SE

The AMG STA-SE is a Special Edition version of NuPrime's AMG STA stereo power amplifier from the AMG series. It pairs a single-ended Class A input module with a Class D output stage, and the SE revision upgrades the switching stage, the feedback resistors and the power supply of the original STA. Owners of an existing AMG STA can have it brought up to SE specification through NuPrime's distributors.

Key specs that matter

Stereo output is 130 W per channel into 8 ohms and 200 W into 4 ohms, and in bridged mode it becomes a 300 W mono amplifier. Input sensitivity is 1.2 V, gain is 26 dB and input impedance is 1 Mohm on XLR and RCA alike. Output impedance is 0.02 ohm. Frequency response runs from 10 Hz to 50 kHz, signal-to-noise reaches 100 dB and THD+N is 0.006%. The case measures 235 x 55 x 300 mm and weighs 4.5 kg.

Engineering and use context

The input module works in single-ended Class A without negative feedback. The Class D output stage uses double feedback and switches at 700 to 750 kHz, and in the SE version its MOSFETs run 30% cooler at these speeds. The feedback sampling uses precision resistors with 0.1% tolerance and a temperature coefficient of 15 ppm, so the feedback stays stable as the chassis warms up, and a retuned secondary feedback loop has been added. Larger supply capacitors and low-impedance routing raise the instantaneous current to 1.5 times that of the original AMG STA. A small switch-mode supply feeds the low-voltage circuits, while a large linear supply powers the Class D stage. Ground shielding against external interference is built into the PCB. The front panel is CNC-milled from 15 mm aluminium alloy, and the slim case runs cool enough to sit on a shelf without large heatsinks.

Pairing

Thanks to the high input impedance, valve and solid-state preamplifiers drive it easily, and the sensitivity matches most line outputs. A single unit in stereo drives most bookshelf and floorstanding speakers, and two bridged units working as monoblocks are the choice for harder loads. The AMG PRA preamplifier stacks directly on top, the small footprint leaves room for a streamer or DAC on the same shelf, and the balanced input suits sources placed some distance away.

Alternatives

NuPrime's STA-9 is a smaller half-width stereo power amplifier.