PASS LABS HPA-1

A $3,500 headphone amp with free preamp, or vice versa?

"Rather than bore you with audiophile cliché after cliché, let’s break it down. The Pass HPA-1 is on the top tier of the world’s finest headphone amplifiers, regardless of cost, end of story. If you can live with the single-ended functionality and a single output, you’ll have a tough time getting better sound anywhere. It is expensive, but delivers the goods. If you are only looking for a headphone amplifier, this is the top of the heap."

MADE IN THE USA

Pass Labs HPA-1 with Phones_photos_v2_x2

Intro

The HPA-1 headphone amplifier was designed ground-up to become what we believe is one of the very best sounding headphone amplifiers available today. With low feedback, wide bandwidth and a direct coupled MOSFET output stage, this musical instrument drives even the most difficult headphone loads with ease, power and grace.

The HPA-1 also functions as a line-level preamplifier that sonically rivals much higher-priced competition. The measured performance is superb and the sound even better.

General Technical Features

Pass Labs’ HPA-1 is capable of delivering full-range dynamics across the entire frequency range, even when driving headphones that present difficult 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 performance. That has been accomplished :

First, by the conceptual approach of designing 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 supply 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 amplifier 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 compromises 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-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..

Summary of Key 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 headphone
Low feedback wide bandwidth discrete design
Class A direct coupled Mosfet output stage
Custom low noise Toroidal power transformer with a Faraday shield
Discrete regulated power supply for audio circuits
Locking Headphone jack
Full function Class A Line Preamplifier offering 2 RCA Inputs and one RCA Line Output

PASS LABS HPA-1 SPECIFICATION

Class of Operation

Class A
Headphone Output Impedance

15 > 600 ohms
Output Impedance - Preamplifier Stage

RCA output < 2 ohms
Preamplifier Gain

8 dB
Headphone Output (Maximum)

3.5W into 20 ohms

200mW into 200 ohms

Headphone Outputs

Locking Neutrik ¼” connector
Inputs

2 x RCA
Input Impedance

50 Kohm
Frequency Bandwidth

Headphone and Line Out / -1dB 10Hz- 100kHz

THD & Noise

0.005% @ 1V Out
Weight

14 lbs
Dimensions

11 x 13.5 x 14 in

Price $ 3,675

What they say ...

TONE Magazine

by Jeff Dorgay | 2021

The HPA-1 is the brainstorm of the newest addition to the Pass team, Jam Somasundram. Speaking with him on the phone is highly enjoyable and he makes it a point to tell me that he “designed the HPA-1 as a linestage first,” giving it the necessary oomph to drive a power amplifier, so that driving headphones would be no problem.

A man of major understatement, this thing is fantastic.

Even if you aren’t a headphone enthusiast, but have been shopping for a linestage in the $15,000 range, consider the HPA-1. (Remember, it’s only $3,500…) If you have a minimalist, yet high performance system and can live with two single-ended inputs and a lone single-ended output to your power amplifier, get your hands on an HPA-1 and spend the rest of the money on your system.

Pairing the HPA-1 with everything in the studio and at home from bare-bones vintage amplifiers up to the Pass Xs300 monoblocks used as the anchor to our main system is a treat. Comparing it to a number of other preamplifiers in the $5,000–$10,000 range, the Pass holds its own or outperforms them in terms of quietness, dynamic range and tonality. Once powered up for a few days, and played for about 100 hours, it opens up further, exhibiting a level of refinement you would expect from a $10k preamplifier. Remember, only two inputs, no remote and one set of outputs. But purely from a sonic standpoint, it is stellar.

From a visual standpoint, it looks like an Xs Pre put in a shrink machine. Its diminutive size is less than half of a standard component, making it great for a compact, yet high performance system, or the perfect desktop headphone amplifier.

Oh yeah, it’s a great headphone amplifier

Pass keeps the minimalist thing going here too. With only a single ¼-inch jack on the front panel, they haven’t addressed the balanced thing, or multiple outputs, merely concentrating on the one way of connecting that most headphones offer. Forget about that; this thing sounds awesome.

The Pass press release mentions that it will easily drive planar phones, and this is instantly confirmed with a quick test drive of HiFiMan, Audeze, and Oppo phones. Even the notoriously tough-to-drive AKG phones pose no threat to the HPA-1.

For those who haven’t had the Pass experience, Nelson Pass has said on more than one occasion, he “likes the sound of tubes, without the hassle,” that is, replacing tubes and the occasional catastrophic failure that can accompany high voltage and high heat. The HPA-1 sounds just like the current crop of Xs gear: refined, dynamic and quiet, with a tonal balance a few molecules to the warm side of neutral. Never a bad thing with today’s current crop of headphones, especially the top of the line Sennheiser phones.

After running through a wide gamut of phones to confirm no rocks in the road, most serious listening was done with the Audeze LCD-2s (current version) and the OPPO PM-1s. While this is a very well-balanced amplifier, its strongest suit is the sheer dynamic range it offers. Much like the Xs300 monoblocks we use daily, this extra dynamic range and grip helps whatever headphones you might have, fully controlling their diaphragm, resulting in quite possibly the most wonderful experience you will have with your current phones. Even my late ’70s vintage Koss Pro4aa’s took on new life with the HPA-1 driving them.

If you’ve ever been in a hifi show room, or trade show where the speaker manufacturer uses a massive power amplifier to drive a small pair of speakers with great result, you know what I’m talking about. It also gives whatever phones you are listening to extra oomph in the bass department. Favorite EDM tracks now really feel weighty, especially with the Audeze phones. As you might expect, the stereo image produced by this amplifier on a premium pair of headphones is big, bold and exciting. A couple of times I caught myself getting up out of the chair, ready to walk away, thinking that I didn’t even have headphones on.

A $3,500 headphone amp with free preamp or vice versa?

Rather than bore you with audiophile cliché after cliché, let’s break it down. The Pass HPA-1 is on the top tier of the world’s finest headphone amplifiers, regardless of cost, end of story. If you can live with the single-ended functionality and a single output, you’ll have a tough time getting better sound anywhere. It is an expensive headphone amplifier, but delivers the goods. If you are only looking for a headphone amplifier, this is the top of the heap.

As the control center of a minimalist hifi system, it offers performance far beyond what you’d expect to get from a $3,500 linestage, and it has a world-class headphone amplifier thrown in for free. Again, if the topology fits your needs, even the most crazed audiophile could live the rest of their days with the HPA-1. It’s that good. Even if you never plug a pair of phones into the front panel and merely use it as a preamplifier, this is one of the best values in high-end audio today. And swing it does.

What they say ... more snippets :

"To put it bluntly, Pass Labs HPA-1 is an exceptional, very addictive headamp/preamp combo every aficionado should at least audition once an opportunity strikes.”
HiFi Knights

” If I did not know that the HPA-1 was transistor-based, I would’ve been fooled : the HPA-1 had the natural warmth and slight fullness that mimic tubes.

In my view, headphone listening is about intimacy, and the HPA-1 is nearly perfect in this regard.”
HometheaterReview.com

“As far as headphones go, the HPA-1 is a brilliant amp which deserves

every bit of praise I’ve thus far heaped on it.”
Part-Time Audiophile

“One Of The Best HPAs In The Audiophile World!”
Everything Audio Network

“The HPA-1 had an effortless quality that made recorded music sound more like the real thing.”
CNET

“Pass Labs, one of the most prestigious names in audio, has launched a terrific headphone amplifier”
Home Theater HiFi

“in bass clarity and authority and in midrange transparency, the Pass Labs HPA-1 is without peer”
Stereophile

“The Pass HPA-1 is on the top tier of the world’s finest headphone amplifiers”
Tone Audio

“This thing sounds so damn good twenty minutes out of the box”
Tone Audio

“An amplifier that drives headphones to exceptional performance”
alpha-audio.nl

“The best I’ve heard from a headphone amp anywhere near the HPA-1’s price.”
Enjoy The Music

“The Pass Labs HPA-1 is a bona fide muscle amp in the guise of an equal-opportunity preamp with head-fi function.”
6Moons

“Dynamics and authority are two of the best qualities in all listening sessions with the HPA-1, regardless of the headphone. With a great current delivery

it also drives any planar-magnetic headphone, with absolute control.”
www.oldnewsound.es

“I think it would be fair to say that the HPA-1 is one of the best headphone amplifiers I have heard.”

Audio Beatnik - Adam Labarge

Awards

Headphone Amplifier of the Year – 2016
The Absolute Sound

Best Headphone Amplifier – Best of Awards – 2016
HomeTheaterHiFi

Blue Note Award 2017
Enjoy the Music

Editors Choice Award
The Absolute Sound

Best Audio Gear – 2018
The Absolute Sound

Recommended Components – 2018
Stereophile

Positive Feedback Brutus Award 2018
Positive Feedback

Stereophile Recommended Components – 2019
Stereophile