Усилители мощности стерео — Nuprime Audio STA-9X

The STA-9X is a compact stereo power amplifier from NuPrime Audio, the company whose engineering team grew out of NuForce. It improves on the STA-9 by borrowing the design concept of NuPrime's high-end AMG-STA, pairing Class A input circuitry with switching output devices. Bridging turns it into a monoblock.

Key specs that matter

NuPrime rates it at 2 x 130 W in stereo and 330 W in bridged mono. Both XLR and RCA inputs present 47 kohm, and a switch selects between them. Output impedance is 0.02 ohms. The Class D stage switches at 750 kHz. Frequency response extends to 50 kHz. Output current capability is 130% higher than the STA-9's.

Engineering and use context

NuPrime's front end is a high-impedance, single-ended circuit without negative feedback, running in Class A, and the power stage is a Class D design with dual feedback. NuPrime describes the combination as ULCAM, an ultra-linear Class A module plus Class D. The input circuit is designed to produce predominantly even-order harmonics. Rather than using a fixed clock, the Class D stage generates its pulse-width modulation with a self-oscillating circuit. At 750 kHz, its switching frequency is far above the 300 kHz or less common in Class D amplifiers, keeping switching products well away from the audio band and allowing a response to 50 kHz. NuPrime's new linear power supply uses a high-efficiency toroidal transformer to reduce high-frequency noise and strengthen low-frequency output, instead of the switch-mode supplies found in many compact Class D amplifiers. The amplifier is reliable with no load connected and has improved short-circuit protection. The higher current capability helps with low-impedance speakers. NuPrime's own isolation feet damp vibration. The chassis measures 55 x 235 x 281 mm, weighs 4 kg, with black and silver finishes. Gain is 29.1 dB, input sensitivity is 1.1 Vrms for rated power, and the rear panel carries 12 V trigger connections in and out. The half-width chassis matches the DAC-9X and Stream-9 in the same series. In bridged mode, one unit drives one speaker. Two units are needed for stereo bridged use.

Pairing

The 47 kohm input impedance suits any preamplifier, including NuPrime's DAC-9X with its volume control. In bridged mono, two STA-9X units drive demanding floorstanders, while one unit in stereo suits most bookshelf speakers.

Alternatives

NuPrime's AMG-STA is the higher-end stereo amplifier of the brand from which the STA-9X takes its design concept.