Instrumental Duet Instrumental Duet,Trombone,Trumpet - Digital Download SKU: A0.783135 By Chicago. By Robert Lamm. Arranged by John Groves. Pop,Rock. Score and parts. 13 pages. John Groves #6064137. Published by John Groves (A0.783135). Trumpet & Trombone Duet edition of Saturday in the Park. Hit chart by Robert Lamm originally performed by Chicago.Includes full score and individual parts.