Power amplifiers stereo — Accuphase A-48S

The Accuphase A-48S is a stereo power amplifier working entirely in Class A, made by the Yokohama company that has built amplifiers in Japan since 1972. It is the fifth generation of the brand's 50 W-class Class A model and replaces the A-48 of 2019. In the same chassis size it gains 5 W per channel into 8 ohms, a damping factor 25% higher and a further 6% less noise.

Key specs that matter

Output in Class A is 50 W per channel into 8 ohms, 100 W into 4 ohms, 200 W into 2 ohms and 400 W into 1 ohm with music signals. Bridged for mono, it delivers 200 W into 8 ohms, 400 W into 4 ohms and 800 W into 2 ohms. Frequency response runs from 0.5 Hz to 160 kHz. THD is 0.03% into 4 to 16 ohms in stereo and 0.05% in bridged mode, intermodulation distortion stays at 0.01% and signal-to-noise reaches 118 dB. The damping factor is 1000. The amplifier measures 465 x 211 x 464 mm and weighs 34.8 kg.

Engineering and use context

Each channel has six parallel push-pull pairs of power MOS-FETs biased for Class A, so the devices conduct over the whole signal cycle and there is no crossover transition. The input stage is an instrumentation amplifier with balanced signal handling, and the gain stages use Accuphase current feedback with MCS+ circuitry, which runs several input circuits in parallel to lower noise. Balanced remote sensing takes the feedback signal from the speaker terminals instead of from inside the amplifier, cancelling the resistance of the internal wiring and supporting the high damping factor. The power supply pairs a large high-efficiency toroidal transformer with two 68000 uF filter capacitors. Protection relies on MOS-FET switches rather than mechanical relays, detects short circuits at the speaker terminals and watches heatsink temperature, and the power meters flash when it trips. The needle meters read from -50 dB, a four-step gain selector offers Max, -3, -6 and -12 dB, and the case sits on high-carbon cast iron feet.

Pairing

Since output doubles each time the load halves down to 1 ohm, the A-48S can drive low-impedance and electrostatic speakers. The gain selector helps match it to sensitive speakers or to high-output preamplifiers such as the Accuphase C-2300 or C-2900. A switch sets bi-amping or bridged operation, so a second unit can be added later and the pair run as mono amplifiers.

Alternatives

The Accuphase A-80 is another Class A stereo power amplifier from the brand.