There are a total of 3 cassette players in the game. I listened to all tapes until the end, so you might want to do that as well.
cassette 1: After entering level 2 and switching on the light, you will see the cassette player in the lower middle of the screen on the table.
cassette 2: In the next area, where the fuse room is on the far left, take the most right door to a briefing room. There is a cassette recorder in the front.
cassette 3: After you opened the Hatch and climbed down a ladder, you are in a very small room with red light. There is a cassette recorder in the lower right of the screen.