[Build] CAPI HPA500, 500 Series Headphone Amplifier, Official Support Thread

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I have a HPA500 that I recently built and functionally everything works but the issue that I am having is that the output is distorted. If I drop the input signal then the HPA500 cleans up until I put the volume back up to compensate. I will review all resistor and component placement but just reaching out to see if there are any common solutions to this distortion issue. Also have to note that the output volume is around 65 to 70db and this is operating in a selected mode of mono.

Thank you for your products and assistance with DIY kits!


There should not be any distortion. There is likely a build error somewhere...

The input will handle +28dBu before rising over 1% THD+N.


I made the great mistake of putting the semiconductors (Q1-4] in backwards on the board. Again everything functioned but the output to the headphones became distorted when the input or output was increased. Goes to show just check the instructions completely!!!! LOL