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Introduction:
Pass Labs’ HPA-1 is capable of delivering full-range dynamics across the entire fre-
quency range, even when driving headphones that present diffi cult loads in terms of
impedance or power consumption or both.
Pass Labs’ designers knew that in order to stand out from the crowd, and satisfy their
demanding customer base, the HPA-1 had to establish higher standards for audio per-
formance. That has been accomplished fi rst, by the conceptual approach of design-
ing the HPA-1 as a real Class-A power amplifi er, and not as an accessory offering only
incremental performance gains. Second, by cutting no corners in circuit design, while
omitting unnecessary frills. Thirdly, by sparing no necessary expense in execution.
The foundation of the HPA-1’s engineering is a custom, low-noise shielded toroidal
power transformer with a Faraday shield between windings as well as a mu-metal
shield around the circumference, feeding a discreet low noise regulated power sup-
ply for the audio circuits. The importance of the power supply is often overlooked and
plays a large part in overall performance of the amplifi er. The HPA-1’s amplifi er circuits
are low-feedback, wide-bandwidth discreet designs employing a J-Fet input stage
and a Mosfet output stage biased into Class A-biased direct-coupled output stage.
The HPA-1 easily drives headphones presenting loads from 15 to 600 Ohms, particularly
excelling on planar headphone designs. The sound is rich and detailed.
The HPA-1 has a single high-quality “locking” headphone jack on its front panel, two
sets of single-ended analog inputs via RCA jacks on the rear panel, and also a set of
switchable “Preamp” line-level output jacks on the rear panel. There are no compro-
mises with the HPA-1 used as a preamp and it will compete against contemporary
preamps. The rear panel holds the power switch and fuse. Volume control is via a
hefty rotary knob connected to an ALPS Potentiometer or circuit. The other front-pan-
el controls are three pushbuttons, to select inputs or to engage the Preamp output.
The substantial casework is the customary and well-recognized brushed aluminum
shared with other Pass Laboratories products.
Thank you for purchasing this “product”. It is my sincere hope that you will enjoy its
sound as much as we do.
Pass Labs
