Here’s a really nice visual introduction to the Steelphon S900.
And here’s some sound demos.
The sound is really fat not unlike the Americans at the time. I guess the organ like parallel octave timbres helps to make rich.
Here’s a cool video of Bowie’s Sens of Doubt from the Heros album. David really shows who’s master at posing. I guess this was recorded to VHS, hence the wobbly Mellotron strings. I don’t know Italian so I don’t have a clue what the speaker says. Feel free to make a translation! The synthesizer in top of the Mellotron is a Steelphon S900 – a very rare Italian made synthesizer from mid 70s. Most probably not the synthesizer used on the track as the S900 is monophonic and the sine plings sound polyphonic.