The LA4520 was a stereo audio amplifier integrated circuit (IC) manufactured by the Sanyo Corporation of Japan. It consisted of a pair of preamplifiers, and a pair of power amplifiers to drive a stereo headphone. It was an extremely popular IC, which was utilised in a wide range of stereo portable devices. It was one of the earliest low-power single-chip stereo cassette player solutions, and the stereo signals from the audio magnetic head fed directly into the preamplifiers, which then fed a pair of power amplifiers to drive a headphone.
The LA45xx series IC usually made a small 'pop' sound when powered; hence, one can tell straight away which chip a walkman had.
Here is a pinout diagram of the Sanyo LA4520 IC. If you are into walkmans and stereo cassette players then this might be interesting for you.
The IC operates between 4.5 V to 6 V with an absolute minimum requirement of 2.7 V. The power dissipation is 520 mW, which makes it a viable component for portable battery powered audio applications.
The power amp provided a fixed 45 dB output, which was adjustable by changing the feedback resistors. This IC also has a ripple filter function, enabled with the addition of a 47-µF capacitor at pin 4. It also has a mute function activated by injecting a positive voltage at pin 13.