An absolutely massive organ/synthesizer combo, issued by Yamaha in the mid-1970s. The voice architecture and circuitry, and the user interfaces, set patterns that Yamaha would use throughout its analog synthesizer line in the 1970s, including the CS80. It was one of the first synths to use voice allocation methods of providing polyphony.
As can be seen in the photo, the GX-1 provides a three-manual keyboard, with two having full-size keys, and the top one (referred to as the "solo" keyboard) having mini keys. All are aftertouch sensitive. A set of bass pedals (just visible at the bottom right) is also provided. There is also a ribbon controller above the solo keyboard, and a plethora of controls to modify various parameters. As in the CS80, many of these are "wheel edge" controls that move in an arc. The groups of buttons at the top center are patch selection buttons.
The top mini keyboard controls a monophonic section. The other two manuals are eight-voice polyphonic, and offer two layers per patch. Both are contained within a single patch selection, although there is a way to split them. The pedal controls an additional monophonic section, which can have up to three layers assigned to it. Full patch programming is not possible from the front panel; some parameters can be modified (not stored), but patch creation required an optional programmer. The factory patch memory takes the form of sets of potentiometers in sets of small cartridges that are contained within the unit; one can be plugged into the programmer and it will tell the user how to trim the pots in the cartridge to duplicate a programmed patch.
All of the synth sections use a basic VCO-VCF-VCA signal chain. These components, however, are very versatile. The VCO offers six different waveforms plus noise. The sawtooth wave can be passed through an internal bandpass filter, and the pulse wave (which has pulse width modulation) can be passed through an internal high pass filter. The VCA actually consists of two filters, a low pass and a high pass; the tracking can be varied between the two, which helps produce many of the sounds characteristic of early Yamaha synths (the CS80 has the same VCF setup). For the solo monophonic section, the VCA includes a ring modulator. Each of these three components has its own envelope generator. A pull-out drawer at the lower left contains controls for detuning the various layers with respect to each other, in order to create chorusing effects. This is just an outline; there is a huge amount of different options which can modify patches in various ways. All together, the instrument contains 36 VCOs. The unit also contained a (non-programmable) drum machine.
At the time it was introduced in 1973, the GX-1's list price was $60,000 US, which is about $300,000 in 2015. This, plus the instrument's mass (it weighed over 650 lbs, or 300 kg), and the fact that it was required to buy a Yamaha amplifier and speaker system to interface with it, naturally limited sales. Most sources estimate that 50-70 were built, and few of these were sold outside of Japan. Notable users included Keith Emerson, who used one on the ELP Works albums, and Led Zeppelin's John Paul Jones, who played one on In Through the Out Door. Emerson purchased Jones' unit after one of his was destroyed when a vehicle crashed into the building where it was stored. Dutch keyboard player Rick Van Der Linden released a solo album performed entirely on a GX-1, including using the built-in drum machine for the drum parts.