Sequential Sequantial is an electronic musical instrument company based in San Francisco. Founded by Dave Smith in 1974 and previously known as Dave Smith Instruments, the company is known for the Prophet synthesizer. Average User Rating 0 0 votes Please sign in to rate. Your Rating 0 Contact Phone Number: +1 (707) 963-7006 Extension 808 Address: 1527 Stockton Street San Francisco, California 95206 U.S.A. Email: support@sequential.com Online: History History coming soon!