Pass Labs X.8 Amplifiers

Nine New Class-A Amps Boast More Power, Fewer Stages, Lower Distortion and Less Feedback

Pass Laboratories just introduced the X.8 (or “Point 8“) Series Amplifiers, which deliver more power, fewer stages, lower distortion and less feedback than ever before. They more accurately represent recording venues through a soundstage whose dimensionality does not change no matter the complexity of the material. In addition, the layering of orchestral instruments by Point 8 Amps allows the orchestra to seem present in the listening room, but with more space and air around the instruments, leading to a greater sensation of musical ease and flow. The bass goes very deep, while the highs extend outward without sounding edgy.

The series consists of five Class-A amplifiers and four Class AB amplifiers, four two-channel and five monoblock models. The two-channel amps include the X150.8, the X250.8, the X350.8 and the XA30.8. The mono models include the X600.8, the XA60.8, the XA100.8, the XA160.8 and the XA200.8. Their per-channel power ratings range from 30 for the two-channel XA30.8 to 600 for the single-channel X600.8.

Pass Labs’ new amplifiers refine superb objective measurements with subjective perceptions. They represent a summation of the company’s knowledge of and expertise in designing amplifiers, while elegantly expressing its philosophy of more amplifier, more progress and more music.

They also demonstrate Pass Labs’ belief that the best products must be carefully adjusted until its various components operate in harmony then subjectively fine-tuned. As a result, Pass Labs subjected the Point.8 amplifiers’ state-of-the-art engineering to an extensive, rigorous listening process using six different sound systems to deliver peak musical experiences.
 
Inspired by Pass Labs’ X.5 Series amplifiers from 2006, the output stages of the larger Point.8 Series have been designed to bias more deeply into the Class-A operating region. They feature large push-pull Class-A operating envelopes for low distortion and good loudspeaker control at ordinary listening levels.

Head of the Class-A
Pass Labs successfully increased the amplifiers’ Class-A operation by employing higher power Toshiba MOSFETs (metal-oxide semiconductor field-effect transistors) than in its earlier amps. MOSFETs are typically used to convert voltage. Those in the Point.8 Series run at a fraction of their stated specs to enhance both performance and reliability.

Pass Labs also installed many more MOSFETs than usual on most Point.8 models. The X250.8 and XA100.8 amplifiers each use 56, while the X350.8, X600.8, XA160.8 and XA200.8 models each use 72.

Pass Labs also improved the amplifiers’ front ends, which house the input and voltage gain stages. Each of the nine Point.8 models has a front end uniquely molded to the specifics of its output stage so that the nine front ends vary in size, voltage, bias current, dissipation, and the distribution of single-ended vs. push-pull bias.

The improvements yield directly coupled (DC) front ends that boast very high stability, low distortion, low noise, 100-Khz open-loop bandwidths, and very high input impedances. Direct coupling in this manner maximizes the performance of each model’s output stage, while imparting to each model its own subtle and unique sonic signature. With the Point.8 Series, Pass Labs moves beyond cookie-cutter circuits.
 
Power to Spare
The power supplies are also larger than those of earlier amplifiers. The X150.8, X250.8, XA30.8, XA60.8, XA100.8, X350.8 and X600.8 models have a third more storage capacitance as well as new CRC (capacitor-resistor-capacitor) filtering to round out the edges of the supply ripple.

The power supplies still use paralleled fast/soft rectifiers and very large toroidal transformers from Plitron, but the AC primary circuits now incorporate additional RF filtering. Power on/off switching and a stand-by draw are also new.

The amplifiers’ front-end circuits boast massively larger power supply decoupling and low-noise shunt regulators that enable unprecedentedly more precise reference voltages for the cascode circuits. In addition, Pass Labs improved the amplifiers’ output noise by more than 10 dB, and made the amplifiers much more resistant to variations in the AC power line.

The smaller Point.8 models — the X150.8, the X250.8, the XA30.8, the XA60.8 and the XA100.8 — also feature new and larger heat sinks, an upgrade that lowers distortion and dissipates the energy of the larger bias currents.

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