High Impedance Class D Headphone Amp?

Hi Barry,

that headphones vary hugely in their load impedances (8...600R) is a huge problem for any headphone amplifier designer. A certain remedy is to use a series resistance at the output of headphone amplifier which automatically reduces the sound level for headphones with lower load impedance. That's why I asked you in your original thread what source resistance your headphones can tolerate.

You may want to have a look at these articles from the awesome and unique Mr. Rod Elliott: 

https://sound-au.com/project70.htm

https://sound-au.com/project113.htm

https://sound-au.com/project24.htm

Kai

Hi Barry,

Are you considering any TI device already? I would suggest to use Class-D amp only if the load physically close to the amplifier, otherwise you would also need to consider adding a filter for long cables.
As Kai mentioned, there are some techniques that can be used to compensate for the different load impedance.

Hi Kai,
Thanks for your comments.

Best regards,
-Ivan Salazar
Applications Engineer

A popular headset is the Bose A20:

 https://assets.bose.com/content/dam/Bose_DAM/Web/consumer_electronics/global/products/headphones/a20_aviation_headset/pdf/746706_og_a20_en.pdf 

I don't see anything that describes required source impedance of the amplifier.  The Bose A20 has a SPL of 92 and impedances of 160/320 ohms. Older driver circuits I've seen did not have a series resistor that I could find.  From what I read the amp output impedance should be under 1/8 the load impedance.  I guess you are suggesting adding the resistor to somewhat automatically accommodate different headset impedances?