This is a vintage 1980 Electro Harmonix Mini-Synthesizer EH 0400 analog synth. Completely intact, including all original multi-colored rubber switch tips and perfectly functional 3″ hard-wired speaker, this particular example is a very excellent simple-sounding analog monosynth, with the ability to slip it into a laptop protective case and transport it anywhere.
The membrane buttons/keys are well preserved, and have not been damaged. The plastic case exterior is also in perfect structural condition with no cracks. The internal speaker works perfectly, as does the aux. 1/8″ output jack.
This particular example is in very nice all original condition and features: a single analog VCO, a single Pulse waveform, an octave divider, a dedicated LFO for a Pulse-Width-Modulation effect, an analog filter, a sweep and phase rate with cutoff controls, as well as in/out of phase, resonance and filter switches.
It was recently cleaned and serviced, and is guaranteed to work perfectly. I recommend using (2) 9v batteries during operation, as the appropriate 18v power supply is rather difficult to procure.