Part of the 1st batch of ESOTECs (not yet named as such), the Sm-7 was directly derived from the Model 300DC but with better specs here and there, ESOTEC oblige.
The two "sub-speaker" sets benefit from the gain pots while the "direct" set circumvents this extra length of wire and solder.
The Japanese versions have a back switch selecting the DC or AC coupling of the inputs, a feature found on 2nd generation ESOTEC such as Ma-5 or Sm-1000.
Inside are four bigga 15,000µF caps, a thermally-matched dual-fet differential circuit makes the input and four "Marantz-developed" 60MHz fT / 200W Pc the output transistors.
Available in black (EU) or in gold (US, JP) with an optional wooden case (US & JP), the Sm-7 was replaced by the fairly similar Sm-9 in mid 1981, the latter being, this time, a strictly Marantz Japan component.