Усилители мощности стерео — Accuphase P-7500

The P-7500 comes from the Japanese maker Accuphase and belongs to its line of Class AB stereo power amplifiers. It follows an earlier model in the same slot and is aimed at owners of large, hard-to-drive loudspeakers.

Key specs that matter

Rated power at 0.05% distortion is 300 W per channel into 8 ohms and 600 W into 4 ohms, with 900 W available into 2 ohms for music signals. Switched to bridged mode, a single chassis delivers 1,200 W into 8 ohms or 1,800 W into 4 ohms. Distortion is quoted at 0.03% across 4 to 16 ohms and IM distortion at 0.01%. The signal-to-noise ratio reaches 130 dB with gain at maximum and 135 dB at the -12 dB setting. Damping factor is 1,000 or greater in normal and bi-amping use. Frequency response spans 20 Hz to 20 kHz within 0.2 dB at rated power and 0.5 Hz to 160 kHz at -3 dB at 1 W. Input sensitivity for full output is 1.95 V. The amplifier is 465 mm wide, 238 mm high and 515 mm deep and weighs 49.0 kg, drawing 142 W at idle and 450 W under the IEC 62368-1 rating.

Engineering and use context

Each channel ends in ten paralleled push-pull power transistors driven through a three-stage Darlington arrangement, which limits the effect of back EMF from the drivers on the final devices. A 12.6 times gain in the input section and 2 times in the power stage give an 11% noise improvement over the predecessor. Its input follows the instrumentation amplifier principle with equal impedance on the plus and minus legs, the voltage amplifier stage runs as a two-way parallel MCS+ circuit claimed to cut the noise floor by about 30%, and current feedback keeps phase behaviour stable at high frequencies. Balanced remote sensing takes feedback from the speaker terminals. The supply combines a large toroidal transformer with 60,000 uF of filtering, and the output stage sits on a large heat sink. Speaker protection uses contactless MOS-FET switches with short-circuit detection.

Pairing

Balanced and line inputs, balanced polarity selection and four gain steps allow matching to many different preamplifiers. Two units can be bridged or used for bi-amping, and the logarithmic power meters read from -50 to +3 dB with a 3 second or infinite peak hold. Accuphase builds versions for 120, 220 and 230 V mains, and standby draw is 0.3 W.

Alternatives

The Accuphase P-4600 is a smaller Class AB stereo power amplifier with six parallel push-pull transistor pairs and 150 W into 8 ohms.