The APA3541/4 is an integrated class AB stereo headphone driver contained in an SO-8 or a DIP-8 plastic package with Mute feature . Besides the common Mute feature , the APA3541/4 further integrates a voltage divider inside the chip . Thus , the external resistors can be eliminated . The APA3541 has a fixed gain of 0dB and the APA3544 has a fixed gain of 6dB so that external gain setting is unnecessary. The device is fabricated in a CMOS process and has been primarily developed for portable digital audio applications .