Усилители мощности моно — Pass Labs Xs 300

The Xs 300 is a pure Class A monoblock power amplifier from Pass Labs, built across two chassis per channel. It was released in 2013, priced in the United States at USD 85,000 per pair and sits in the Xs range together with the Xs 150 monoblock. Each channel is a control chassis placed on top of a separate current-source chassis, with the two linked by cable. Each box measures 48.3 cm wide, 69.9 cm deep and 27.9 cm high, and the two weigh about 61 kg and 78 kg.

Key specs that matter

Rated output is 300 W into 8 ohm in Class A and 600 W into 4 ohm, with up to 48 A of peak output current. Gain is 26 dB, and the input panel carries XLR as well as RCA sockets. Pass quotes 112 output devices per channel, a damping factor of 200, output noise of 100 uV and response from 1.5 Hz to 100 kHz, with 1 percent distortion at 1 kHz at full power. Power draw is 900 W in use and under 1 W in standby.

Engineering and use context

Inside, 36 pairs of transistors, 18 on each half of the push-pull circuit, and another 40 devices in the lower chassis act as constant current sources. That arrangement gives the output stage a single-ended bias character while it stays push-pull in structure. The rated output stays in Class A, and above that point the amplifier moves into Class B for peaks. A front panel meter shows the bias state, and its needle swings to the right once output goes past the Class A limit. Each monoblock runs from a 2 kVA transformer and 400,000 uF of filter capacitance, an unusually large reserve for a single channel, built from 16 capacitors of 25,000 uF. With a heavy draw from the wall for every channel even at idle, most of that energy leaves as heat, so the heatsinks need open space and the room temperature rises during long sessions. A stereo pair means four boxes and a total of more than 270 kg, so the rack or floor platform has to carry that load, and each box needs to be placed where its cable to the partner chassis can reach.

Pairing

The moderate gain and the choice of balanced or single-ended inputs make the Xs 300 a straightforward partner for the Xs Preamp, which was launched alongside it. Doubling of power into a halved load and the large current reserve give headroom for low-impedance speakers with difficult load curves. Two dedicated mains circuits are sensible, since each monoblock alone draws so much power.

Alternatives

The Pass Labs Xs 150 is the smaller two-chassis Class A monoblock in the same range, for rooms or speakers that do not call for the larger model's output.