Pass Labs HPA-1 Headphone Amp
The Pass Labs HPA-1 is a Class A headphone amp that was designed to amplify headphones with impedances of 15 ohms to 600 ohms.
It 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.
- 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.
|Output Power into 20 ohms||3500mW|
|Output Power into 300 ohms||200 mW|
|Frequency Response 10hz-100k||-1dB|
|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|
The HPA-1 is a single ended device. I was going to use balanced monoblocks with it and I am now more disappointed that it took me close to 2 years from my initial demo to purchase. My advice is to grab this piece and bi amp or bury larger amps if you must - THE HPA-1 is THAT GOOD for my pre-amp and for my headphone amp. I have and still do own several tube headphone amps. None of the 5 very high quality midrange tube amps can match the sound of the headphone amp in the HPA-1 and though I have a very simple pre-amp, it replaced Nelson’s old Bride of Zen which I built and tweaked over 15+ years. The Bride is retired. Long live the Pass. If I had a “con” it would be having to get Drew to sell me a balanced to 1/4” phone plug. Not a bad price to pay for the last headphone amp I may ever own.
8 months ago
Switch to Morphine the sax and bass were just as pin point and lush. I tried to listen to a wide variety of music. I headed to the Ws and found Widespread Panic: simply amazing. I can go on and on but you need to check out Mr. Somasundram's masterpiece for headphones.
Two of my personal favorite demos are Crazy & Killer by Seal. Who knows what a synthesizer is supposed to sound like?
I'll say, if it sounds good then i'm happy. Killer had dynamics that I rarely, if ever think about - with the PASS the quieter passages are still full of detail and when the bass & drums come along, they literally pop out and grab me.
I concluded with Bonnie Raitt - I think i'm in love!