Generally thought to be the first electronic music instrument, the first Telharmonium was built by Thaddeus Cahill in 1897. The instrument was conceptually similar to, although much more complex than, a Hammond organ. It used a bank of tone generators, which probably output a waveform close to but not quite a sine wave, and a set of mixing controls to synthesize different waveforms; as such, it can be considered an additive synthesis instrument. Note that at the time, de Forest had yet to invent the triode tube, and so there was no such thing as an audio amplifer. That meant that the Telharmonium's tone generators had to generate enough power for the waveform to drive a loudspeaker directly. As a result, the tone generators were in fact high-voltage electrical generators, geared to run at different speeds. A complex keyboard switching mechanism selected the right generators corresponding to the harmonics of each played note. The tone generator banks and the engines required to run them were massive; they filled over a dozen railroad cars and took up several floors of a building when installed.
Cahill's concept was that the Telharmonium's music would be performed live and distributed into homes via the telephone system. Some trials were performed in the 1906-1915 timeframe, but there was little demand for the strange-sounding music, and telephone subscribers complained of crosstalk that resulted when the Telharmonium's waveforms excited resonances in the primitive telephone systems of the time.
Possibly as many as three Telharmoniums were built, but no artifacts exist today except a few photos. After Cahill died in 1934, his family tried for years to interest a museum in the one remaining Telharmonium, but found no takers; they finally scrapped it in 1962. No recordings of the Telharmonium are known to exist.