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Pass Labs HPA-1 Headphone Amp


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Pass Labs HPA-1 is a Class A headphone amp that was designed to amplify headphones with impedances of 15 ohms to 600 ohms.

Pass Labs' HPA-1 Headphone Amplifier can deliver full-range dynamics across the entire frequency range. The HPA-1 can even drive headphones that present difficult loads in terms of impedance, power consumption or both.

In order to stand out from the crowd, Pass Labs conceptually designed the HPA-1 as a real Class-A power amplifier, not as an accessory offering only incremental performance gains. The HPA-1 cuts no corners in the circuit design and spares no necessary expense in execution.

The foundation of the HPA-1's engineering is a custom, low-noise shielded toroidal power transformer feeding a discreet low noise regulated power supply for the audio circuits. The importance of the power supply is often overlooked and plays a large part in the overall performance of the amplifier.

The HPA-1's amplifier circuits are low-feedback, wide-bandwidth discreet designs employing J-Fet input stages and Class A-biased direct-coupled MOSFET output stages.

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 headphone jack on the 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 compromises with the HPA-1 when used as a stereo preamp, and it will compete against contemporary preamplifiers. The rear panel holds the power switch and fuse. Volume control is via a hefty rotary knob connected to an ALPS Potentiometer. The other front-panel 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.

Main Features:

  • Works with headphones with impedances of 15 ohms to 600 ohms.
  • Designed as a power amplifier rather than a typical headphone amplifier to be able to drive low impedance planar headphones.
  • Low feedback wide bandwidth discreet design.
  • Class A direct coupled Mosfet output stage.
  • Custom low noise Toroidal power transformer with a Faraday shield.
  • Discreet regulated power supply for audio circuits.


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Product Reviews

Output Power into 20 ohms 3500mW
Output Power into 300 ohms 200 mW
Frequency Response 10hz-100k -1dB
Gain 8 dB
THD + Noise < 0.005 at 1V out
Input Impedance 50K Ohm
Output Impedance < 2 ohms
Power Consumption 6 Watts
Dimensions  4.5" H x 11" W x 13" D
Weight 14lbs

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