I actually owned a Mellotron, way way back, around 1973 or so. It was very difficult to press the keys, as I remember, but so cutting edge at the time (string sounds).
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Yamaha 920 / Yamaha DGX-670 / Maui 5 Go (2) / Senn e935 / Sony C80 / Tascam DP24sd / ATEM Mini Pro switcher (studio)