Усилители мощности стерео — Accuphase P-4600

The P-4600 is a Class AB stereo power amplifier from Accuphase, the fourth generation of the P-4000 series since the P-4100 of 2008. The series continues the line of Accuphase's standard Class AB power amplifiers that began with the P-300 in 1973, and the P-4600 replaces the P-4500. Above it in the Accuphase catalogue sits the larger P-7500. The US retail price is about USD 13,975.

Key specs that matter

Rated output is 150 W per channel into 8 ohm, 300 W into 4 ohm and 450 W into 2 ohm, compared with 90, 180 and 360 W for the P-4500. In bridged mono mode it delivers 600 W into 8 ohm and 900 W into 4 ohm. The guaranteed signal to noise ratio is 125 dB and output noise is 19.5 µV, and the guaranteed damping factor is 800. Frequency response is 0.5 Hz to 160 kHz. Each channel uses six parallel push-pull pairs of 150 W, 15 A bipolar transistors, two pairs more than in the P-4500. It accepts signals through a single RCA pair or a single XLR pair and has two pairs of large speaker terminals. The amplifier measures 465 x 190 x 427 mm and weighs 30.0 kg.

Engineering and use context

Paralleling six transistor pairs per channel lowers the output impedance and spreads the current across more devices, which is why the damping factor rose to 800 and the amplifier stays stable into very low impedances. The fully balanced input stage works on the instrumentation-amplifier principle, equalising the impedance on the positive and negative sides so external noise is rejected, and it provides a high gain of 12.6 times. Amplification uses current feedback together with the MCS+ circuit. Balanced remote sensing takes feedback from both the signal line and ground near the speaker terminals, further lowering output impedance and reducing distortion. Speaker protection relies on a MOSFET switch with an on-resistance of 1.6 mOhm instead of a mechanical relay, short circuits are detected by photo-couplers, and temperature sensors monitor the heat sinks. Left and right channels are built as separate amplifier blocks with their own heat sinks, in a monoblock layout around a large custom toroidal transformer and two 50,000 µF filter capacitors. The gain selector offers Max, -3, -6 and -12 dB settings and changes the input stage gain rather than attenuating the signal, lowering residual noise with sensitive speakers. Analogue power meters read down to -50 dB.

Pairing

With its large power reserve and stability into low impedances, the P-4600 drives large and low-impedance loudspeakers. Accuphase preamplifiers connect through the balanced XLR input, and the two terminal pairs allow bi-wiring or two sets of speakers.

Alternatives

The Accuphase P-7500 is the larger Class AB stereo power amplifier in the same catalogue.