Усилители мощности стерео — Nuprime Audio STA-9

The STA-9 belongs to the 8 and 9 Series of NuPrime Audio, a hybrid two-channel design sold at USD 799 in black or silver. It supports bridged mono use and adds even-order harmonic (H2) circuitry. Its design derives from the ULCAM and Class-D combination first introduced in the IDA-8.

Key specs that matter

Power is quoted at 2 x 120 W or 1 x 290 W into 8 and 4 ohm, with peak output of 2 x 280 W or 1 x 320 W. Gain is 26.85 dB in stereo and 32.46 dB in mono, equal to voltage gain of 22 and 42. Input sensitivity is 232.8 mV for 1 W into 8 ohm and 1.4 V to rated power. Input impedance is 47 kohm and output impedance is 20 milliohm. THD+N is 0.02 percent in stereo and 0.01 percent in mono, dynamic range spans -115 dB to 0 dB at 1 kHz, and frequency response runs from 10 Hz to 50 kHz. Connections comprise one RCA input, one XLR input and one set of speaker outputs used in stereo or mono.

Engineering and use context

The front end is a single-ended JFET circuit shared with the HPA-9 headphone amplifier, adding second harmonics in the manner of a triode, and its bandwidth reaches 300 kHz with very low negative feedback. NuPrime notes that this raised second harmonic content gives a measured signal-to-noise figure above 90 dB. A self-oscillating PWM circuit clocks the Class-D output stage at 550 kHz, whereas NuPrime says most class-D amps switch at 300 kHz or lower. The signal path avoids coupling capacitors, giving response down to DC. A new linear power supply with a toroidal transformer feeds the circuit, and NuPrime isolation feet damp vibration. Protection covers no-load operation and short circuits. Mono mode uses Single-Ended Direct-Inject Bridge Technology in place of an op-amp inverter. Idle consumption is below 14 W on 110 V and below 16 W on 230 V, and mains voltage is set to 115 or 230 V by a selector. The case measures 55 x 235 x 281 mm and weighs 4 kg, and the warranty is one year. A 3 A slow-blow fuse guards the mains input.

Pairing

NuPrime cites high output current capability for low-impedance speakers. The toggle switch only configures the inputs, so RCA and XLR should not be connected together. The speaker outputs have no DC offset, with the negative terminal at ground, so a subwoofer can be fed from them.

Alternatives

The NuPrime AMG STA offers 2 x 130 W into 8 ohm, with a 700 kHz Class D stage and 1 Mohm input impedance.