X-Altra HPA-1 Class A Headphone Amplifier

The HPA-1 is a compact high performance class A headphone amplifier that will deliver up to 1.75W into a 32 Ohm pair of headphones. The amplifier features ultra-low distortion, very wide bandwidth and class A operation up to 13 V pk-pk into 32 Ohms. Beyond 13V pk-pk into 32 Ohms, the OPS transitions to class AB operation.

The circuit combines a dual ultra-low distortion opamp, the LM4562, with a discrete power output stage. The design has been tested and measured using OPA1642 and NE5532A opamps and he performance remains outstanding. The complete amplifier, including the opamps, runs in class A. Into 60 Ohm headphones and above, the HPA-1 remains fully in class A up to the rated 21 V pk-pk output swing (note, it will actually swing a few volts higher on higher load impedance headphones).

Here’s a short 3 1/2 minute YouTube video about the HPA-1

The document below discusses the design and presents the measurements:-

The Excel spreadsheet below contains the BOM with Mouser Part Numbers (updated `14 Oct 2021):-

The price of the HPA-1 PCB is $15.99 plus $16 tracked and signed shipping. You can get 2 boards for $30 and the same shipping cost. Shipping takes 5-7 working days after we mail the items.

HPA-1 PCB Only

HPA-1 + Standard PSU Bundle

You can also buy a HPA-1 PCB + Standard PSU bundle for $35.99 plus $16 tracked and signed shipping – click on the button below. Please allow 5-7 working days after we mail the items.

Kindly contact me at bonsai(at)hifisonix.com if you want to but PCB’s

Here are a new set of measurements I did where I replaced the LM4562 opamps with FET input OPA1642 devices. The measurements are very good, and the capacitive load driving ability also excellent.