Def Leppard's first album was one of producer Mutt Lange's many masterpieces, with layer upon layer of stacked parts that fit perfectly together. Here's the isolated vocal track from "Foolin',"one of the hits from that album. Here's what to listen for (the quality isn't that great, unfortunately).
1. The lead vocal is compressed pretty hard, but it works perfectly in the context of the mix.
2. The vocals have an interesting gated reverb effect that blooms and then cuts off instead of the normal decay that you'd hear. Some mixers and producers used to refer to this as the "cloud" sound.
3. You don't think of Def Leppard as a keyboard oriented band but there sure are a lot of synths on this song, especially the low synth on the B sections and coming out of the solo.
4. Listen to the stacked background vocal harmonies at 4:10. It almost sounds like the background vocals on The Cars early albums.