The BOSS Bass Synthesizer SYB-3 offers a wide variety of sounds. The leftmost knob is broken. The part of the knob you turn has broken off. Sound still comes out, of course. The back cover uses four screws, but currently has two. - Model Name: Bass Synthesizer SYB-3 - Output Type: OUTPUT A (MONO) - Input Type: INPUT - Adapter Type: BOSS PSA Adapter only - Control Knobs: EFFECT, FREQ, DIRECT, SENS - Color: Silver Thank you for looking.