The embedded headphone "amp" is probably just a good-enough chip amp.

内置的耳机功放或许只是一片还不错的功放芯片。

youdao

This paper introduces the principles of IN AMP chip AD620, and the feature parameters and main characterial curves, it also presents some typical application circuits.

本文简要概述了单片仪器放大器AD620的结构原理及其性能特点和主要关系曲线，并给出了一些典型应用。

youdao

Launched by BBK spin-off Vivo in Beijing just now, this 5.7-inch Xplay takes one step further from its smaller X1 and X1S cousins by packing one extra audio chip, the OPA2604 op amp from Texas Instruments, in order to add extra oomph to Cirrus Logic's CS4398 DAC and CS8422 stereo asynchronous sample-rate converter -- both of which are featured on the X1 series.

ENGADGET