We start with simple FET circuits already having low distortion and noise, and arrange them in two symmetrical halves. The two halves of the amplifier channel are closely matched, eliminating a large portion of distortion and noise without feedback. A small amount of feedback is also applied, not so much for the purpose of reducing distortion but to make the distortion as identical as possible on both polarities of the balanced output.

It is easier to make distortions more identical than to remove them with feedback, and this is the operating principle of X amplifiers.

Since the X1000, Pass Labs products have continuously evolved toward higher performance. The Class AB “X” series was joined by the Class A “XA” amplifiers. Subsequent improvements to the Class AB “X” amplifiers resulted in the “X.5” products, and their phenomenal success has led to the Class A “XA.5” series.

As always the goal has been the best musical and objective performance possible with minimal parts in the signal path and minimal feedback. This process is not completely understood, and many of the improvements are the result of trial and error and extensive listening.

Measurement of performance is important to us, and we feel that well-designed product sounds good and measures good. Apparently it is possible to make an amplifier which measures well but which does not please the ears, and so we let our ears be the final judge.

X.5 and XA.5 amplifiers utilize the same basic circuit topology and gain devices. They differ in the sizes of the power supplies, the chassis and heat sinks, and the number of output devices. The output stages of the X.5 series are operated in heavily biased Class AB, with an idling dissipation similar to the rated output. The XA amplifiers operate pure Class A with idling dissipation more than twice the rated output.

Within any given chassis size, the X and XA amplifiers are designed to dissipate about the same power, and it is not surprising that this leads to two channel amplifiers with half the output power per channel of comparable mono amplifiers, and Class A amplifiers with half the output of Class AB amplifiers.

The X amplifiers deliver more output power per dollar, and the XA amplifiers have a better subjective performance. All of the amplifiers drive known loudspeaker loads without misbehaving, and all are unconditionally stable into low impedance and reactive loads.

XA30.5 Owner’s Manual

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Pass Labs Amplifier, 5XA30.5 owner manual
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Amplifier, 5XA30.5 specifications

Pass Labs has long been synonymous with high-performance audio amplification, and their 5XA30.5 amplifier is a testament to their commitment to quality and engineering excellence. The 5XA30.5 is an exceptional Class A amplifier designed for audiophiles seeking purity in sound reproduction. One of its standout features is its power output; delivering 30 watts per channel into 8 ohms and a doubled output into 4 ohms, it provides ample power for driving a range of loudspeakers with ease.

One of the key technologies employed in the 5XA30.5 is its Class A circuitry. Unlike other amplification classes that switch on and off to produce sound, Class A amplifiers operate continuously, ensuring that the signal remains uncorrupted. This results in a rich, warm sound that faithfully represents the original recording. The design eliminates crossover distortion, a common issue in other classes of amplification, thus enabling the 5XA30.5 to deliver detailed and smooth audio performance, even at lower volumes.

The amplifier's robust construction further enhances its performance. With a fully balanced differential input stage, the 5XA30.5 minimizes noise and distortion, ensuring that the sound remains crisp and clear. The use of custom-designed output transistors offers superior linearity and thermal stability. Additionally, the generous power supply, equipped with a hefty transformer and ample capacitance, allows the amplifier to handle dynamic peaks without strain, preserving the integrity of the audio signal.

Another notable characteristic of the 5XA30.5 is its elegant design. The aesthetics include a minimalist chassis, machined aluminum front panel, and dual meters that provide real-time performance feedback, allowing audiophiles to observe the amplifier’s operation. Furthermore, it features both single-ended and balanced inputs, offering compatibility with a variety of source components.

Importantly, the 5XA30.5 embodies Pass Labs' philosophy of "the art of amplifier design," resulting in a product that not only performs exceptionally well but also maintains a timeless appeal. Whether for critical listening or enjoying music in a relaxed setting, the Pass Labs 5XA30.5 amplifier promises an unparalleled auditory experience, fulfilling the demands of even the most discerning audiophile. In a landscape where many amplifiers prioritize features over fidelity, the 5XA30.5 remains a beacon of true sound reproductions, demonstrating that exceptional quality and craftsmanship can coexist harmoniously.
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