Slightly modified, subbing the two single op amps of the original to a dual. 1458 or 4558 should match the spec of the original ones.
Boss FA-1 FET Amplifier
Tools, Tones and Toys for Guitarists
Slightly modified, subbing the two single op amps of the original to a dual. 1458 or 4558 should match the spec of the original ones.