Input & Output connected backwards

Hello, A couple years ago, the father of my gf gave me this Cassette player, seems to work ok, the vumeters got light, and I made a noob mistake, as i'm familiarized with more "digital" devices. My intention was to use it as a vumeter, by connecting the source to the vumeter, then connect it to the amp, and my "surprise" was that i heard like something popped, and i thought it was the fuse, (now i know, the source is the cassette player itself going to an amp, and then to the speakers) I changed the fuse and still not working. i'm not able to see if there's something burnt. Could be the new fuse be bad too? Thanks in advance!!