TB-303
"The TB-303 is a dedicated sequencer/bass-machine. It was originally released by Roland to be paired with the TR- 606 drum machine. The idea was to provide an inexpensive substitute for a live drummer and bass player. The TR- 606 outsold its bass counterpart considerably, and ironically the 303 is worth considerably more now. It does a pretty poor imitation of a bass guitar. The unit is drum-machine-sized (if you've seen a 606, it's the same case pretty much). It has buttons arranged in a keyboard configuration for entering pitches, plus various other buttons for editing sequences. There are knobs controlling the tuning, frequency cutoff, resonance, envelope amount and decay, plus volume and tempo. There is a DIN sync jack on the back for synchronization with the outside world (found on the 606, 808, 202, etc.). This is a 1-oscillator synth, with essentially a single EG. You can select either square or sawtooth waveforms. Programming sequences into it is extremely bizarre, and almost impossible to figure out if you don't have a manual (or someone to tell you how). You enter the pitches first, and then enter the durations in a second pass. You also go back and enter accents and slides later. Not exactly user-friendly. What is it about the 303 that gives it that mystical sound? Ask 6 people and you'll get 7 opinions. Reasons I've heard or proposed (although I don't agree with all of them):
the filter is a 3-pole filter, which has a unique sound
there's something screwy going on with the resonance in there
the accent alters the resonance amount and envelope too, not just the volume.
the slide feature is totally unlike regular portamento and can't be emulated.
the sequencer's screwy interface makes you accidentally enter bizarre lines.
I personally think the sequencer is key, especially the slide. Yes, the synth has a unique sound, but it's not much by itself."