Who made the GX1, one of the largest, most expensive, (at the time), polyphonic analog synthesizers?

The GX-1 was Yamaha's first big polyphonic analog synthesizer publicly released in 1975. First released as the Electone GX-707, Yamaha developed it as a test bed for later consumer synths and organs for stage and home use.

Considered the predecessor to the CS-80 (another huge poly-synth), the GX-1 featured a triple-tiered keyboard, pedalboard, ribbon controller, eight polyphonic voices, chromed pedestals and a $50,000+ US dollar price tag. It wasn't designed for your everyday musician, less than 10 were ever made and have been owned mostly by legendary synth/keyboard players including Keith Emerson, John Paul Jones of Led Zeppelin, Stevie Wonder, Rick Wright, George Fleury, Richard James of Aphex Twin, ABBA, and Hans Zimmer who bought Keith Emerson's.

Although it may look like an organ, it's all analog inside. The two main keyboards have 61 (velocity sensitive) keys each, and are supplemented by a smaller (3/4 scale, pressure sensitive) 37-note keyboard and a 25-note pedalboard at your feet for 184 total keys. Eight voices of polyphony plus an additional monophonic are available and can be shared and layered or split among the different keyboards. There are also organ-style drawbars and a ribbon controller for tweaking the sounds. Additional programming buttons are hidden away under drawers and panels on the front.

It was truly a lush synth for its time, and the many rock legends who used it helped cement its place in history.