Усилители мощности стерео — Accuphase A-80

The A-80 is a two-channel Class A power amplifier from Accuphase of Japan, developed as a stereo counterpart to the A-300, the monaural model the company built for its 50th anniversary. Both channels share one chassis, and the company describes the design as a fusion of new noise reduction work with the experience gathered over its five decades of amplifier building.

Key specs that matter

Rated output into 8 ohms is 65 W per channel, rising to 130 W into 4 ohms and, for music signals, 260 W into 2 ohms and 520 W into 1 ohm. Bridged, one A-80 gives 260 W into 8 ohms and 520 W into 4 ohms. Total harmonic distortion is 0.03% from 4 to 16 ohms and 0.07% into 2 ohms, with intermodulation at 0.01%. At rated output the response holds flat within 0.2 dB from 20 Hz to 20 kHz, and at 1 W it extends from 0.5 Hz to 160 kHz at -3 dB. Accuphase specifies a damping factor of 1,000 or greater and quotes 123 dB of signal-to-noise with gain at maximum. The chassis is 465 mm wide, 240 mm high and 515 mm deep and weighs 44.6 kg net. Idle consumption is 211 W, which reflects Class A biasing.

Engineering and use context

Each channel drives its load through a Class A output stage of ten push-pull MOS-FET pairs wired in parallel. Gain is split between a fully discrete input section at 22 dB and the power stage at 6 dB, a distribution Accuphase says lowers output noise by 7% against earlier models. The input works on the instrumentation amplifier principle, the voltage stage uses two paralleled MCS+ circuits, and current feedback keeps the upper frequency response steady when gain is switched. Balanced remote sensing returns both signal and ground from the speaker terminals to hold the damping figure. A large toroidal transformer feeds 120,000 uF of filter capacitance. Protection uses MOS-FET switches with no mechanical contacts, edgewise-wound coils sit in the output path, and the power circuit boards are glass cloth fluorocarbon resin.

Pairing

Balanced XLR (40 kilohm) and RCA (20 kilohm) inputs, polarity switching for the balanced connectors and a four-step gain control of 28, 25, 22 or 16 dB make it easy to match most preamplifiers. Two A-80 units can run in bridged or dual mono mode, or in bi-amping with one unit on each speaker band. Bar graph and digital power meters with a switchable hold time sit on the front, and the 230 V version switches off after 120 minutes without a signal.

Alternatives

The Accuphase A-48S is a smaller Class A stereo amplifier with six parallel MOS-FET pairs per channel rated at 50 W into 8 ohms.