A Power Amp for Headphones: Pass Labs' HPA-1

by The Audio Beat | December 2, 2015

ass Labs’ new HPA-1 headphone amplifier ($3500) is said to be "capable of delivering full-range dynamics across the entire frequency range, even when driving headphones that present difficult loads." The HPA-1 drives headphones with loads from 15 to 600 ohms, "particularly excelling on planar headphone designs." In concept the HPA-1 is a class-A power amplifier whose foundation is a custom, low-noise, shielded toroidal power transformer feeding a low-noise regulated power supply. The HPA-1’s amplifier circuits are low-feedback, wide-bandwidth designs employing J-FET input stages and class-A direct-coupled MOSFET output stages.

The HPA-1 has a single 1/4" headphone jack on its front panel, two sets of single-ended analog inputs via RCA jacks on the rear panel and a set of switchable line-level output jacks, so the HPA-1 can be used as a stereo preamp. Volume control is via a large knob connected to an ALPS potentiometer. The other front-panel controls are three pushbuttons used to select the input or engage the line-level outputs.