Not sure of the four versions-am only aware of three options. One, and the least expensive, uses the standard cj polystyrene caps. The second, and the version I'm finishing reviewing for positive feedback, uses the new Teflon caps but comes san transformer (this unit uses three higher gain 12AX7s to give a gain value of 53 dB). It also only has one phono input. The third version also uses the teflon caps and comes with a transformer for low output MCs (this unit uses 6DJ8s) and has two inputs of differing gain values (not sure of the values).