Усилители мощности стерео — Accuphase A-48S

The A-48S is a pure Class A stereo power amplifier from Accuphase, the Yokohama manufacturer that has built amplifiers in Japan since 1972. It is the fifth generation of the company's 50 W-class Class A model and replaces the A-48 of 2019, raising output by 5 W per channel into 8 ohms, lifting the damping factor by 25% and cutting noise by a further 6% within the same chassis size.

Key specs that matter

Rated output is 50 W per channel into 8 ohms, 100 W into 4 ohms, 200 W into 2 ohms and 400 W into 1 ohm (music signals), all in Class A. Bridged mono output is 200 W into 8 ohms, 400 W into 4 ohms and 800 W into 2 ohms. Frequency response extends from 0.5 Hz to 160 kHz. THD is 0.03% into 4 to 16 ohms in stereo and 0.05% bridged, intermodulation distortion 0.01%, and signal-to-noise reaches 118 dB. The damping factor is 1000. The chassis measures 465 x 211 x 464 mm and weighs 34.8 kg.

Engineering and use context

Six parallel push-pull pairs of power MOS-FETs per channel form the output stage, biased for Class A, so the devices conduct over the full signal cycle and no crossover transition occurs. The input section is built as an instrumentation amplifier with balanced signal handling, and the gain stages use Accuphase's current feedback topology with MCS+ circuitry, which places several input circuits in parallel to lower noise. Balanced remote sensing takes the feedback signal from the speaker terminals rather than from inside the amplifier, which cancels the resistance of internal wiring and supports the high damping factor. The power supply combines a large high-efficiency toroidal transformer with two 68000 uF filter capacitors. Protection uses MOS-FET switches rather than mechanical relays, detects short circuits at the speaker terminals and monitors heatsink temperature, and the power meters flash when a fault trips it. Needle meters read from -50 dB, a four-step gain selector offers Max, -3, -6 and -12 dB, and the unit stands on high-carbon cast iron feet.

Pairing

Because output doubles each time the load halves down to 1 ohm, the A-48S drives low-impedance and electrostatic speakers without strain, though its moderate 8 ohm rating suits speakers of 87 dB or more in rooms up to about 30 m2. The gain selector matches it to sensitive speakers or high-output preamplifiers such as Accuphase's C-2300 or C-2900. A switch selects bi-amping or bridged operation, so two units can later run as mono amplifiers.

Alternatives

Accuphase's A-75 is the larger Class A stereo power amplifier with higher output and a bigger power supply.