Some time ago I bought a pair of in ear headphones and I am very pleased with them, but I don't have a decent headphone amplifier for them at home. So I searched the web and became very interested in building a headphone amplifier BUF634 and OPA627 combination. I decided to use the circuit in figure 5. from the BUF634 datasheet, in this configuration the amplifier operates in class A up to approx. 14-15 mW with a 32 ohm headphone, which is more than enough for me. We have finished the amplifier now and I am very pleased the sound, plenty of bass with in ear headphones and otherwise a clear and precise sound.
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