I've been working on my personal 1964 comp, and listening to the songs, i've noticed that the Motown mono mixes from this period, in particular, sound so spectacular. The have lots of depth, a great sense of space, and very laid back and mellow, almost audiophile, in a way. I notice this most on hits by The Temptations, Martha & The Vandellas, Marvin Gaye, and The Supremes. The songs before and after don't quite sound so great, especially for 1965.

This is a question for those who were there, or who are schooled on the gear they used: what makes those mono mixes from this particular time period sound so good? What gear did they use at the time? Bob Olhsson?