The sounds of the PSS-140 are generated using 2-operator FM from the Yamaha YM2413 chip and it sounds similar to the OPL2 and OPL3 computer sound cards of the late 1980's and early 1990's (AdLib and Sound Blaster). If you want a selection of instruments with the "FM sound", but don't want to learn how to program an FM synthesizer (it's hard!), the PSS-140 has a great collection of sounds that can be considered representative of what FM is good at, including organ, bass, synth brass, electric piano, synth strings, and melodic percussion sounds.
The 11-step volume control can be thought of as a bitcrusher plugin -- reducing the volume steals bits of resolution from the audio output, so sounds are more grainy and lo-fi at lower volume. At any volume the output is pretty noisy.
Although it's made of plastic, the build quality is such that you'll be shopping for a new knee rather than a new keyboard if you try to snap it over your knee.
Year Released: 1988
Keyboard: 37 mini keys
Polyphony: 6 notes
ROM: 100 instruments, 10 rhythms, 5 drum sounds
Dimensions: 565.5 mm x 195.8 mm x 62.4 mm
Weight: 1.5 kg
This keyboard has built-in 2-watt mono speaker(s).
Batteries: AA x 6