hifisonix

Hifisonix HPA-1 Class A Headphone Amplifier

Written by

bonsai

in

The circuit combines a dual ultra-low distortion opamp, the LM4562 or OPA1642, with a class A discrete power output stage to deliver outstanding performance both measured, and sonically. 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).

Click here for the HPA-1 BOM

Click here to buy PCBs for the HPA-1 Headphone amp over in the shop

Attention: Listening to music at elevated sound pressure levels can permanently damage your hearing.

The document below discusses the design and presents the measurements (updated with latest PCB’s etc 15 May 2023):-

Hifisonix HPA-1 Headphone Amplifier Sept 2024


The slides below show how to wind the output inductors L1 and L2 over the 3.3 Ohm output resistors 

HPA1 May 2023 – How to Wind L1 and L2

The picture below shows how to wire the Hifisonix Standard PSU, which has a built in Mute function, to the HPA-1.  This will prevent any power ON/OFF  noises

 

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.

X-Altra HPA-1 with OPA1642 OpampsDownload

Comments

8 responses to “Hifisonix HPA-1 Class A Headphone Amplifier”

  1. admin avatar
    admin

    Hello Steve, thanks for your comments.

    Yes, we do combined shipping to save on costs and are working to bring this to the shop.

    In the meantime, just email me with your requirements to bonsai(at)hifisonix.com.

    Regards

    Andrew

  2. Steve avatar
    Steve

    Hi, I’m interested in this board as well as some of others that you’ve designed.

    Do you offer combined shipping for purchasing multiple boards? I only see how to purchase one board at a time (each with its own shipping cost).

    Thanks!

  3. Bonsai avatar
    Bonsai

    Arlo, the output offset is controlled by the 2nd opamp. The typical offset is 1 mV, worst case 3.5 mV.

    Hope this helps to answer your question.

  4. Arlo avatar
    Arlo

    Hi Andrew.
    Excellent circuit!
    I would like to ask about the output DC offset from power up to stabilized.
    For the first look of this circuit, I don’t see the part to control the output offset.

    Regards

  5. Bonsai avatar
    Bonsai

    Hi Nick, thanks for your question. Its basically the same amplifier but slightly tweaked. The original design did not run the 2nd stage opamp properly in class A – the X-Altra HPA-1 does.

  6. Nick Smith avatar
    Nick Smith

    Hi Andrew.

    Is X-Altra Mini II HPA-1 a replacement of Hifisonix HPA-1 ?
    And what’s wrong with the old version ?

    Regards

    Nickson

  7. Bonsai avatar
    Bonsai

    Hi Nickson,

    I’m working with a guy from diyAudio who is designing one. Will take a few more weeks.

    Cheers

    Andrew

  8. Nickson avatar
    Nickson

    Hi Andrew

    How about PCB for this project?

    Regards

    Nickson

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