Power amplifiers mono — Pass Labs XA 200.8

The XA200.8 is a pure Class A monoblock in the Point.8 generation from Pass Laboratories, a family of nine amplifiers spanning the XA and X lines. It runs its output stage in Class A without any microprocessor-controlled sliding bias, and a stereo system needs two chassis, one for each channel.

Key specs that matter

The rating per chassis is 200 W into 8 ohm. Gain is fixed at 26 dB, and an input of 2 V drives the amplifier to full output. Response extends from 1.5 Hz up to 100 kHz. Input impedance is 50 kohm single-ended and 100 kohm balanced, and the damping factor is 200. Idle consumption reaches 760 W per chassis. The case is 483 mm wide, 699 mm deep and 279 mm tall, and each monoblock weighs 71.2 kg.

Engineering and use context

Pass describes the design as aimed at large rooms and live-like listening levels, with the headroom that the high rating brings. The Point.8 revision gave all models bigger power supplies than their predecessors, with roughly a third more storage capacitance and new CRC filtering built from a capacitor, resistor and second capacitor. Its input and voltage gain circuitry was redesigned for each model individually, so the front end of the XA200.8 is sized to its own output stage in voltage, bias current, dissipation and how bias is divided between single-ended and push-pull operation. A porthole display on the front panel indicates output stage bias instead of acting as a power meter. Since fixed Class A bias draws the same heavy current at all times, each amplifier releases a great deal of heat during every listening session and needs generous ventilation. At this depth the chassis will not fit many standard equipment racks, and floor placement on a dedicated amp stand is the more practical choice. Two units together pull more than 1.5 kW from the wall at idle, so a dedicated mains circuit is worth planning for.

Pairing

The gain and full-power sensitivity match the output of typical preamplifiers. With the high balanced input impedance, preamps with limited current drive can still feed long balanced runs to amps placed near the speakers. The rating and damping factor suit large low-efficiency floorstanding speakers whose impedance curves dip low.

Alternatives

The Pass Labs XA160.8 is the next mono Class A model down in the same series, rated at 160 W into 8 ohm in a shallower chassis.