How they made Ring Ring by Benny Andersson
Benny Andersson appeared on March 13,2012 on the Swedish TV show, Låtarna som förändrade musiken (The songs that changed Music)". It is broadcast by the Swedish educational Channel, UR. In this show, he describes how "Ring Ring" was recorded in 1973 using the original tapes. Benny gives a lot of credit to Michael B. Tretow for the group's "Wall of sound" techniques.
The whole series of shows could be found on the show's website (I'm not sure if that's still the case) , but on Youtube, you'll find a couple of versions with English subtitles that were put up by Sadlookinmoon. The most revelatory parts are in the latter part of the video where you get to hear various tracks from the original recording separated out.