Wish you were hear......nice album that when your chilling to some cold beers. Yep, 1975...that makes it easier....as there were practically no polysynths around back then. I'll go listen to the album now and get back to you....but im thinking its possible some kinda organ through effects or a Yamaha GX-1.
Blade Runner is a film soundtrack unlike any other.....to this day it still sounds timeless. Amazing synth sounds and composition. However, vangelis worked on it during 1981....a few years before the first DX7 rolled off the production line. If you check this clip out of the maestro himself....you may recognise some of the sounds from the film....CS80 cross modulation by the sounds of it.
Look at the video here >>
http://www.arturia.net/samples/videos/vtmahm.mpeg
DS