What makes the Pass Labs HPA-1 a standout headphone amplifier?

The Pass Labs HPA-1 is designed more like a power amplifier than a typical headphone amp. It features a high-bias Class A operation with a discrete JFET input stage and a MOSFET output stage, providing high power and excellent sound quality. Its design ensures low noise and wide bandwidth, making it suitable for a wide range of headphones from 15 to 600 ohms​. It has excellent tonality and midrange, making it a solid choice for audiophiles everywhere.

Can the HPA-1 drive high-impedance headphones effectively?

Yes, the HPA-1 can drive high-impedance headphones, such as the Beyer Dynamics DT880 with 600 ohms, with ease. Users report that it delivers good dynamics and volume even with hard-to-drive headphones, demonstrating its robust power and stability​.

How does the HPA-1 perform as a preamplifier?

In addition to being a high-quality headphone amplifier, the HPA-1 also functions as a capable line preamplifier. It has two single-ended inputs and can be used for general system duties, although it lacks a remote control and balanced connections. Its minimalist design is appreciated for its simplicity and high performance​. The input impedance, output impedance, and the overall output power make the HPA-1 a versatile piece of audiophile equipment.

What is the build quality of the Pass Labs HPA-1?

The HPA-1 boasts exceptional build quality, consistent with other Pass Labs products. It features a robust chassis made of brushed aluminum and includes high-quality components such as a custom toroidal transformer with mu-metal shielding to reduce noise​. The large volume knob is a design delight.

Why does the HPA-1 not include an internal DAC?

Pass Labs chose not to include an internal DAC in the HPA-1 to ensure longevity and timelessness. DAC technology evolves rapidly, often becoming obsolete within a few years. By separating the amplifier from the DAC, Pass Labs ensures that the HPA-1 remains a relevant high-end audio and high-performing piece of equipment for many years​.

How does the sound quality of the HPA-1 compare with other high-end headphone amplifiers?

he HPA-1 delivers a spacious soundstage, vivid detail retrieval, and excellent dynamics. It competes with and sometimes outperforms amplifiers that are much more expensive, providing smooth, non-fatiguing sound with a natural presentation of vocals and instruments​.

What is the power output of the Pass Labs HPA-1 Headphone Amplifier?

The Pass Labs HPA-1 offers a robust power output suitable for a wide range of headphones. It delivers up to 3.5 Watts in 32 ohms, providing ample power for demanding high-impedance headphones. This ensures a clean and dynamic sound even at higher volumes, maintaining fidelity and clarity.

Does the Pass Labs HPA-1 support balanced headphone connections?

No, the Pass Labs HPA-1 features only single-ended headphone outputs. It includes a 1/4-inch (6.35mm) stereo single-ended output.

What type of volume control does the Pass Labs HPA-1 use?

The Pass Labs HPA-1 utilizes a precision-stepped relay volume control, providing accurate and repeatable volume adjustments. This design ensures precise level matching between left and right channels, maintaining the integrity of the audio signal. Users can easily fine-tune the volume to their preference with the smooth and reliable stepped attenuator.

Who is Nelson Pass?

Nelson Pass, the man behind Pass Labs and First Watt, has been designing and building amplifiers for decades. His early passion, however, was speakers; at age 14, he started assembling loudspeakers. As a college student studying physics at the University of California-Davis, he co-founded a speaker company called PMA. He also worked for ESS, where he designed crossovers and enclosures. After college, with his interest having shifted toward amplifiers, Pass co-founded Threshold Electronics (now Threshold Audio). His achievements during the Threshold years include developing the first dynamically biased Class A amplifier circuit; developing a fully cascode audio power amplifier; and developing the STASIS stereo preamplifier and power amplifier. During the 1980s, Pass designed the Adcom GFA-555 amplifier. Later, after selling Threshold, he started Pass Labs in 1991 and First Watt in 1997. Pass holds several patents related to audio circuits.

How did Pass Labs make its name?

Pass Labs helped popularize solid-state, Class A power amplifiers. Pass Labs' first product, the Aleph 0 amplifier, operated as a single-ended Class A up to its 70-watt rating and in push-pull Class A at higher wattage. The Aleph series of amplifiers, some of the first solid-state amps that were said to be "tube-like" in sound, operated pure class A and contained internal circuitry using MOSFETs. The Aleph amplifiers had a unique appearance, a cube with heat sinks on all four sides, a solution to the heat generated by the class-A design. This can be attributed primarily to the specific MOSFETs used and the minimum number of gain stages that were implemented in the design. Pass Labs also developed the Super-Symmetry™ ("Su-Sy") circuit, which achieves exceptionally low distortion and noise levels. In 1998, Pass Labs released the X1000, the first amplifier using the patented SuperSymmetric™ topology. The X1000 achieved 1000 watts with high performance, local feedback, and only two gain stages: a cascaded differential pair of transistors and a large bank of complementary output followers. This groundbreaking design informed all subsequent Pass Labs amplifiers.

What else does Pass Labs make?

In 2002, Pass Labs unveiled the first XA amplifiers, combining the X and Aleph topologies into balanced single-ended Class A amplifiers with many of the characteristics of both the X and Aleph series. The current Pass Labs lineup includes Class A amps (XA and Xs Series), Class AB amps (.8 Series), line preamps (Xs and XP Series), phono preamps (Xs and XP Series), integrated amps (INT Series), and one headphone amp.

What is the relationship between Pass Labs and First Watt?

When he started Pass Labs, Pass did everything out of his home. In 1997, having outgrown the space, Pass Labs moved into commercial space in Foresthill, California. When Pass started First Watt, it was a "kitchen table" venture, with work once again happening in his home. In 2016, with production demands not leaving him enough time to pursue the vast array of yet-to-be-designed amps, Nelson handed the business end of First Watt over to Pass Labs. Pass Labs took over the building of First Watt amplifiers as well as marketing and distribution. There's a synergy between the two operations, in that Pass Labs gets to gather up some of the more interesting First Watt finds and repurpose them as more commercially viable designs. Today, Pass splits his time between First Watt and Pass Laboratories.