Power amplifiers mono — Pass Labs XA100.8

The XA100.8 is a mid-sized pure Class A monoblock from Pass Laboratories and one of the nine Point.8 amplifiers in the XA and X ranges. It sits below the XA160.8 and above the XA60.8 in the mono Class A line, and a stereo setup uses two chassis.

Key specs that matter

Pass rates the output at a conservative 100 W continuous into 8 ohm and 200 W into 4 ohm, all in Class A, and the output stage remains in Class A up to 212 W peak. Gain is 26 dB, with full power reached at 1.41 V input. Pass quotes the frequency response from 1.5 Hz to 100 kHz. Input impedance is 50 kohm on RCA and 100 kohm on XLR, and the damping factor is 200. Each unit draws 500 W at idle, a figure that stays the same whether music is playing or the amplifier is simply switched on and waiting. The chassis is 483 x 540 x 229 mm (width, depth, height) and weighs 44.91 kg.

Engineering and use context

Inside, 56 power MOSFETs make up the output section, the same count used in the X250.8. Pass feeds it from an overbuilt toroidal transformer supplying a large capacitor bank. For the Point.8 generation Pass enlarged the supplies with about a third more storage capacitance than the earlier models, and added new CRC filtering made of two capacitors separated by a resistor. Input and gain circuits were reworked for every model, so the XA100.8 front end is scaled to its own output stage, with its own voltage, bias current, dissipation and mix of single-ended and push-pull bias. Its front carries a big analog dial, lit in blue, that registers the steady current drawn by the output devices. For connection, each monoblock offers one gold-plated RCA input and one balanced XLR input, used one at a time. Its case is lower than those of the larger XA monos, which makes the XA100.8 easier to fit on a shelf, though its fixed Class A bias still produces steady heat and needs space for ventilation.

Pairing

Given the moderate full-power input level, almost any line stage or DAC with volume control can drive the XA100.8. Output that doubles as impedance halves points to stable current delivery into lower impedance speakers, and the rating suits monitors and floorstanders of average or higher efficiency.

Alternatives

The Pass Labs XA60.8 is the next monoblock down in the Point.8 Class A family, rated at 60 W into 8 ohm in a lower chassis.